New upstream version 1.47.0~beta.2+dfsg1

CONTRIBUTING.md

@@ -4,5 +4,12 @@ Thank you for your interest in contributing to Rust!
 
 To get started, read the [Getting Started] guide in the [rustc-dev-guide].
 
+## Bug reports
+
+Did a compiler error message tell you to come here? If you want to create an ICE report,
+refer to [this section][contributing-bug-reports] and [open an issue][issue template].
+
 [Getting Started]: https://rustc-dev-guide.rust-lang.org/getting-started.html
 [rustc-dev-guide]: https://rustc-dev-guide.rust-lang.org/
+[contributing-bug-reports]: https://rustc-dev-guide.rust-lang.org/contributing.html#bug-reports
+[issue template]: https://github.com/rust-lang/rust/issues/new/choose

Cargo.toml

@@ -2,9 +2,9 @@
 members = [
   "src/bootstrap",
   "src/rustc",
-  "src/libstd",
-  "src/libtest",
   "src/librustc_codegen_llvm",
+  "library/std",
+  "library/test",
   "src/tools/cargotest",
   "src/tools/clippy",
   "src/tools/compiletest",
@@ -13,10 +13,12 @@ members = [
   "src/tools/rustbook",
   "src/tools/unstable-book-gen",
   "src/tools/tidy",
+  "src/tools/tier-check",
   "src/tools/build-manifest",
   "src/tools/remote-test-client",
   "src/tools/remote-test-server",
   "src/tools/rust-installer",
+  "src/tools/rust-demangler",
   "src/tools/cargo",
   "src/tools/rustdoc",
   "src/tools/rls",
@@ -55,6 +57,18 @@ overflow-checks = false
 # per-crate configuration isn't specifiable in the environment.
 codegen-units = 10000
 
+# These dependencies of the standard library implement symbolication for
+# backtraces on most platforms. Their debuginfo causes both linking to be slower
+# (more data to chew through) and binaries to be larger without really all that
+# much benefit. This section turns them all to down to have no debuginfo which
+# helps to improve link times a little bit.
+[profile.release.package]
+addr2line.debug = 0
+adler.debug = 0
+gimli.debug = 0
+miniz_oxide.debug = 0
+object.debug = 0
+
 # We want the RLS to use the version of Cargo that we've got vendored in this
 # repository to ensure that the same exact version of Cargo is used by both the
 # RLS and the Cargo binary itself. The RLS depends on Cargo as a git repository
@@ -63,21 +77,28 @@ codegen-units = 10000
 [patch."https://github.com/rust-lang/cargo"]
 cargo = { path = "src/tools/cargo" }
 
-[patch.crates-io]
+[patch."https://github.com/rust-lang/rustfmt"]
 # Similar to Cargo above we want the RLS to use a vendored version of `rustfmt`
 # that we're shipping as well (to ensure that the rustfmt in RLS and the
 # `rustfmt` executable are the same exact version).
 rustfmt-nightly = { path = "src/tools/rustfmt" }
 
+[patch.crates-io]
 # See comments in `src/tools/rustc-workspace-hack/README.md` for what's going on
 # here
 rustc-workspace-hack = { path = 'src/tools/rustc-workspace-hack' }
 
-# See comments in `tools/rustc-std-workspace-core/README.md` for what's going on
+# See comments in `library/rustc-std-workspace-core/README.md` for what's going on
 # here
-rustc-std-workspace-core = { path = 'src/tools/rustc-std-workspace-core' }
+rustc-std-workspace-core = { path = 'library/rustc-std-workspace-core' }
-rustc-std-workspace-alloc = { path = 'src/tools/rustc-std-workspace-alloc' }
+rustc-std-workspace-alloc = { path = 'library/rustc-std-workspace-alloc' }
-rustc-std-workspace-std = { path = 'src/tools/rustc-std-workspace-std' }
+rustc-std-workspace-std = { path = 'library/rustc-std-workspace-std' }
+
+# This crate's integration with libstd is a bit wonky, so we use a submodule
+# instead of a crates.io dependency. Make sure everything else in the repo is
+# also using the submodule, however, so we can avoid duplicate copies of the
+# source code for this crate.
+backtrace = { path = "library/backtrace" }
 
 [patch."https://github.com/rust-lang/rust-clippy"]
 clippy_lints = { path = "src/tools/clippy/clippy_lints" }

README.md

@@ -157,17 +157,6 @@ by manually calling the appropriate vcvars file before running the bootstrap.
 > python x.py build
 ```
 
-### Building rustc with older host toolchains
-It is still possible to build Rust with the older toolchain versions listed below, but only if the
-LLVM_TEMPORARILY_ALLOW_OLD_TOOLCHAIN option is set to true in the config.toml file.
-
-* Clang 3.1
-* Apple Clang 3.1
-* GCC 4.8
-* Visual Studio 2015 (Update 3)
-
-Toolchain versions older than what is listed above cannot be used to build rustc.
-
 #### Specifying an ABI
 
 Each specific ABI can also be used from either environment (for example, using

config.toml.example

@@ -341,7 +341,10 @@
 # Debuginfo for tests run with compiletest is not controlled by this option
 # and needs to be enabled separately with `debuginfo-level-tests`.
 #
-# Defaults to 2 if debug is true
+# Note that debuginfo-level = 2 generates several gigabytes of debuginfo
+# and will slow down the linking process significantly.
+#
+# Defaults to 1 if debug is true
 #debuginfo-level = 0
 
 # Debuginfo level for the compiler.
@@ -391,8 +394,7 @@
 # desired in distributions, for example.
 #rpath = true
 
-# Emits extraneous output from tests to ensure that failures of the test
+# Emits extra output from tests so test failures are debuggable just from logfiles.
-# harness are debuggable just from logfiles.
 #verbose-tests = false
 
 # Flag indicating whether tests are compiled with optimizations (the -O flag).
@@ -431,7 +433,7 @@
 #
 # LLD will not be used if we're cross linking or running tests.
 #
-# Explicitly setting the linker for a target will override this option.
+# Explicitly setting the linker for a target will override this option when targeting MSVC.
 #use-lld = false
 
 # Indicates whether some LLVM tools, like llvm-objdump, will be made available in the
@@ -454,8 +456,7 @@
 # instead of LLVM's default of 100.
 #thin-lto-import-instr-limit = 100
 
-# Map all debuginfo paths for libstd and crates to `/rust/$sha/$crate/...`,
+# Map debuginfo paths to `/rust/$sha/...`, generally only set for releases
-# generally only set for releases
 #remap-debuginfo = false
 
 # Link the compiler against `jemalloc`, where on Linux and OSX it should
@@ -474,6 +475,10 @@
 # This only applies from stage 1 onwards, and only for Windows targets.
 #control-flow-guard = false
 
+# Enable symbol-mangling-version v0. This can be helpful when profiling rustc,
+# as generics will be preserved in symbols (rather than erased into opaque T).
+#new-symbol-mangling = false
+
 # =============================================================================
 # Options for specific targets
 #
@@ -502,7 +507,7 @@
 # Linker to be used to link Rust code. Note that the
 # default value is platform specific, and if not specified it may also depend on
 # what platform is crossing to what platform.
-# Setting this will override the `use-lld` option for Rust code.
+# Setting this will override the `use-lld` option for Rust code when targeting MSVC.
 #linker = "cc"
 
 # Path to the `llvm-config` binary of the installation of a custom LLVM to link

git-commit-hash

@@ -1 +1 @@
-04488afe34512aa4c33566eb16d8c912a3ae04f9
+84b047bf64dfcfa12867781e9c23dfa4f2e6082c

library/alloc/Cargo.toml

@@ -0,0 +1,33 @@
+[package]
+authors = ["The Rust Project Developers"]
+name = "alloc"
+version = "0.0.0"
+autotests = false
+autobenches = false
+edition = "2018"
+
+[dependencies]
+core = { path = "../core" }
+compiler_builtins = { version = "0.1.10", features = ['rustc-dep-of-std'] }
+
+[dev-dependencies]
+rand = "0.7"
+rand_xorshift = "0.2"
+
+[[test]]
+name = "collectionstests"
+path = "tests/lib.rs"
+
+[[bench]]
+name = "collectionsbenches"
+path = "benches/lib.rs"
+test = true
+
+[[bench]]
+name = "vec_deque_append_bench"
+path = "benches/vec_deque_append.rs"
+harness = false
+
+[features]
+compiler-builtins-mem = ['compiler_builtins/mem']
+compiler-builtins-c = ["compiler_builtins/c"]

library/alloc/benches/btree/map.rs

@@ -0,0 +1,586 @@
+use std::collections::BTreeMap;
+use std::iter::Iterator;
+use std::ops::RangeBounds;
+use std::vec::Vec;
+
+use rand::{seq::SliceRandom, thread_rng, Rng};
+use test::{black_box, Bencher};
+
+macro_rules! map_insert_rand_bench {
+    ($name: ident, $n: expr, $map: ident) => {
+        #[bench]
+        pub fn $name(b: &mut Bencher) {
+            let n: usize = $n;
+            let mut map = $map::new();
+            // setup
+            let mut rng = thread_rng();
+
+            for _ in 0..n {
+                let i = rng.gen::<usize>() % n;
+                map.insert(i, i);
+            }
+
+            // measure
+            b.iter(|| {
+                let k = rng.gen::<usize>() % n;
+                map.insert(k, k);
+                map.remove(&k);
+            });
+            black_box(map);
+        }
+    };
+}
+
+macro_rules! map_insert_seq_bench {
+    ($name: ident, $n: expr, $map: ident) => {
+        #[bench]
+        pub fn $name(b: &mut Bencher) {
+            let mut map = $map::new();
+            let n: usize = $n;
+            // setup
+            for i in 0..n {
+                map.insert(i * 2, i * 2);
+            }
+
+            // measure
+            let mut i = 1;
+            b.iter(|| {
+                map.insert(i, i);
+                map.remove(&i);
+                i = (i + 2) % n;
+            });
+            black_box(map);
+        }
+    };
+}
+
+macro_rules! map_find_rand_bench {
+    ($name: ident, $n: expr, $map: ident) => {
+        #[bench]
+        pub fn $name(b: &mut Bencher) {
+            let mut map = $map::new();
+            let n: usize = $n;
+
+            // setup
+            let mut rng = thread_rng();
+            let mut keys: Vec<_> = (0..n).map(|_| rng.gen::<usize>() % n).collect();
+
+            for &k in &keys {
+                map.insert(k, k);
+            }
+
+            keys.shuffle(&mut rng);
+
+            // measure
+            let mut i = 0;
+            b.iter(|| {
+                let t = map.get(&keys[i]);
+                i = (i + 1) % n;
+                black_box(t);
+            })
+        }
+    };
+}
+
+macro_rules! map_find_seq_bench {
+    ($name: ident, $n: expr, $map: ident) => {
+        #[bench]
+        pub fn $name(b: &mut Bencher) {
+            let mut map = $map::new();
+            let n: usize = $n;
+
+            // setup
+            for i in 0..n {
+                map.insert(i, i);
+            }
+
+            // measure
+            let mut i = 0;
+            b.iter(|| {
+                let x = map.get(&i);
+                i = (i + 1) % n;
+                black_box(x);
+            })
+        }
+    };
+}
+
+map_insert_rand_bench! {insert_rand_100,    100,    BTreeMap}
+map_insert_rand_bench! {insert_rand_10_000, 10_000, BTreeMap}
+
+map_insert_seq_bench! {insert_seq_100,    100,    BTreeMap}
+map_insert_seq_bench! {insert_seq_10_000, 10_000, BTreeMap}
+
+map_find_rand_bench! {find_rand_100,    100,    BTreeMap}
+map_find_rand_bench! {find_rand_10_000, 10_000, BTreeMap}
+
+map_find_seq_bench! {find_seq_100,    100,    BTreeMap}
+map_find_seq_bench! {find_seq_10_000, 10_000, BTreeMap}
+
+fn bench_iteration(b: &mut Bencher, size: i32) {
+    let mut map = BTreeMap::<i32, i32>::new();
+    let mut rng = thread_rng();
+
+    for _ in 0..size {
+        map.insert(rng.gen(), rng.gen());
+    }
+
+    b.iter(|| {
+        for entry in &map {
+            black_box(entry);
+        }
+    });
+}
+
+#[bench]
+pub fn iteration_20(b: &mut Bencher) {
+    bench_iteration(b, 20);
+}
+
+#[bench]
+pub fn iteration_1000(b: &mut Bencher) {
+    bench_iteration(b, 1000);
+}
+
+#[bench]
+pub fn iteration_100000(b: &mut Bencher) {
+    bench_iteration(b, 100000);
+}
+
+fn bench_iteration_mut(b: &mut Bencher, size: i32) {
+    let mut map = BTreeMap::<i32, i32>::new();
+    let mut rng = thread_rng();
+
+    for _ in 0..size {
+        map.insert(rng.gen(), rng.gen());
+    }
+
+    b.iter(|| {
+        for kv in map.iter_mut() {
+            black_box(kv);
+        }
+    });
+}
+
+#[bench]
+pub fn iteration_mut_20(b: &mut Bencher) {
+    bench_iteration_mut(b, 20);
+}
+
+#[bench]
+pub fn iteration_mut_1000(b: &mut Bencher) {
+    bench_iteration_mut(b, 1000);
+}
+
+#[bench]
+pub fn iteration_mut_100000(b: &mut Bencher) {
+    bench_iteration_mut(b, 100000);
+}
+
+fn bench_first_and_last(b: &mut Bencher, size: i32) {
+    let map: BTreeMap<_, _> = (0..size).map(|i| (i, i)).collect();
+    b.iter(|| {
+        for _ in 0..10 {
+            black_box(map.first_key_value());
+            black_box(map.last_key_value());
+        }
+    });
+}
+
+#[bench]
+pub fn first_and_last_0(b: &mut Bencher) {
+    bench_first_and_last(b, 0);
+}
+
+#[bench]
+pub fn first_and_last_100(b: &mut Bencher) {
+    bench_first_and_last(b, 100);
+}
+
+#[bench]
+pub fn first_and_last_10k(b: &mut Bencher) {
+    bench_first_and_last(b, 10_000);
+}
+
+const BENCH_RANGE_SIZE: i32 = 145;
+const BENCH_RANGE_COUNT: i32 = BENCH_RANGE_SIZE * (BENCH_RANGE_SIZE - 1) / 2;
+
+fn bench_range<F, R>(b: &mut Bencher, f: F)
+where
+    F: Fn(i32, i32) -> R,
+    R: RangeBounds<i32>,
+{
+    let map: BTreeMap<_, _> = (0..BENCH_RANGE_SIZE).map(|i| (i, i)).collect();
+    b.iter(|| {
+        let mut c = 0;
+        for i in 0..BENCH_RANGE_SIZE {
+            for j in i + 1..BENCH_RANGE_SIZE {
+                black_box(map.range(f(i, j)));
+                c += 1;
+            }
+        }
+        debug_assert_eq!(c, BENCH_RANGE_COUNT);
+    });
+}
+
+#[bench]
+pub fn range_included_excluded(b: &mut Bencher) {
+    bench_range(b, |i, j| i..j);
+}
+
+#[bench]
+pub fn range_included_included(b: &mut Bencher) {
+    bench_range(b, |i, j| i..=j);
+}
+
+#[bench]
+pub fn range_included_unbounded(b: &mut Bencher) {
+    bench_range(b, |i, _| i..);
+}
+
+#[bench]
+pub fn range_unbounded_unbounded(b: &mut Bencher) {
+    bench_range(b, |_, _| ..);
+}
+
+fn bench_iter(b: &mut Bencher, repeats: i32, size: i32) {
+    let map: BTreeMap<_, _> = (0..size).map(|i| (i, i)).collect();
+    b.iter(|| {
+        for _ in 0..repeats {
+            black_box(map.iter());
+        }
+    });
+}
+
+/// Contrast range_unbounded_unbounded with `iter()`.
+#[bench]
+pub fn range_unbounded_vs_iter(b: &mut Bencher) {
+    bench_iter(b, BENCH_RANGE_COUNT, BENCH_RANGE_SIZE);
+}
+
+#[bench]
+pub fn iter_0(b: &mut Bencher) {
+    bench_iter(b, 1_000, 0);
+}
+
+#[bench]
+pub fn iter_1(b: &mut Bencher) {
+    bench_iter(b, 1_000, 1);
+}
+
+#[bench]
+pub fn iter_100(b: &mut Bencher) {
+    bench_iter(b, 1_000, 100);
+}
+
+#[bench]
+pub fn iter_10k(b: &mut Bencher) {
+    bench_iter(b, 1_000, 10_000);
+}
+
+#[bench]
+pub fn iter_1m(b: &mut Bencher) {
+    bench_iter(b, 1_000, 1_000_000);
+}
+
+const FAT: usize = 256;
+
+// The returned map has small keys and values.
+// Benchmarks on it have a counterpart in set.rs with the same keys and no values at all.
+fn slim_map(n: usize) -> BTreeMap<usize, usize> {
+    (0..n).map(|i| (i, i)).collect::<BTreeMap<_, _>>()
+}
+
+// The returned map has small keys and large values.
+fn fat_val_map(n: usize) -> BTreeMap<usize, [usize; FAT]> {
+    (0..n).map(|i| (i, [i; FAT])).collect::<BTreeMap<_, _>>()
+}
+
+// The returned map has large keys and values.
+fn fat_map(n: usize) -> BTreeMap<[usize; FAT], [usize; FAT]> {
+    (0..n).map(|i| ([i; FAT], [i; FAT])).collect::<BTreeMap<_, _>>()
+}
+
+#[bench]
+pub fn clone_slim_100(b: &mut Bencher) {
+    let src = slim_map(100);
+    b.iter(|| src.clone())
+}
+
+#[bench]
+pub fn clone_slim_100_and_clear(b: &mut Bencher) {
+    let src = slim_map(100);
+    b.iter(|| src.clone().clear())
+}
+
+#[bench]
+pub fn clone_slim_100_and_drain_all(b: &mut Bencher) {
+    let src = slim_map(100);
+    b.iter(|| src.clone().drain_filter(|_, _| true).count())
+}
+
+#[bench]
+pub fn clone_slim_100_and_drain_half(b: &mut Bencher) {
+    let src = slim_map(100);
+    b.iter(|| {
+        let mut map = src.clone();
+        assert_eq!(map.drain_filter(|i, _| i % 2 == 0).count(), 100 / 2);
+        assert_eq!(map.len(), 100 / 2);
+    })
+}
+
+#[bench]
+pub fn clone_slim_100_and_into_iter(b: &mut Bencher) {
+    let src = slim_map(100);
+    b.iter(|| src.clone().into_iter().count())
+}
+
+#[bench]
+pub fn clone_slim_100_and_pop_all(b: &mut Bencher) {
+    let src = slim_map(100);
+    b.iter(|| {
+        let mut map = src.clone();
+        while map.pop_first().is_some() {}
+        map
+    });
+}
+
+#[bench]
+pub fn clone_slim_100_and_remove_all(b: &mut Bencher) {
+    let src = slim_map(100);
+    b.iter(|| {
+        let mut map = src.clone();
+        while let Some(elt) = map.iter().map(|(&i, _)| i).next() {
+            let v = map.remove(&elt);
+            debug_assert!(v.is_some());
+        }
+        map
+    });
+}
+
+#[bench]
+pub fn clone_slim_100_and_remove_half(b: &mut Bencher) {
+    let src = slim_map(100);
+    b.iter(|| {
+        let mut map = src.clone();
+        for i in (0..100).step_by(2) {
+            let v = map.remove(&i);
+            debug_assert!(v.is_some());
+        }
+        assert_eq!(map.len(), 100 / 2);
+        map
+    })
+}
+
+#[bench]
+pub fn clone_slim_10k(b: &mut Bencher) {
+    let src = slim_map(10_000);
+    b.iter(|| src.clone())
+}
+
+#[bench]
+pub fn clone_slim_10k_and_clear(b: &mut Bencher) {
+    let src = slim_map(10_000);
+    b.iter(|| src.clone().clear())
+}
+
+#[bench]
+pub fn clone_slim_10k_and_drain_all(b: &mut Bencher) {
+    let src = slim_map(10_000);
+    b.iter(|| src.clone().drain_filter(|_, _| true).count())
+}
+
+#[bench]
+pub fn clone_slim_10k_and_drain_half(b: &mut Bencher) {
+    let src = slim_map(10_000);
+    b.iter(|| {
+        let mut map = src.clone();
+        assert_eq!(map.drain_filter(|i, _| i % 2 == 0).count(), 10_000 / 2);
+        assert_eq!(map.len(), 10_000 / 2);
+    })
+}
+
+#[bench]
+pub fn clone_slim_10k_and_into_iter(b: &mut Bencher) {
+    let src = slim_map(10_000);
+    b.iter(|| src.clone().into_iter().count())
+}
+
+#[bench]
+pub fn clone_slim_10k_and_pop_all(b: &mut Bencher) {
+    let src = slim_map(10_000);
+    b.iter(|| {
+        let mut map = src.clone();
+        while map.pop_first().is_some() {}
+        map
+    });
+}
+
+#[bench]
+pub fn clone_slim_10k_and_remove_all(b: &mut Bencher) {
+    let src = slim_map(10_000);
+    b.iter(|| {
+        let mut map = src.clone();
+        while let Some(elt) = map.iter().map(|(&i, _)| i).next() {
+            let v = map.remove(&elt);
+            debug_assert!(v.is_some());
+        }
+        map
+    });
+}
+
+#[bench]
+pub fn clone_slim_10k_and_remove_half(b: &mut Bencher) {
+    let src = slim_map(10_000);
+    b.iter(|| {
+        let mut map = src.clone();
+        for i in (0..10_000).step_by(2) {
+            let v = map.remove(&i);
+            debug_assert!(v.is_some());
+        }
+        assert_eq!(map.len(), 10_000 / 2);
+        map
+    })
+}
+
+#[bench]
+pub fn clone_fat_val_100(b: &mut Bencher) {
+    let src = fat_val_map(100);
+    b.iter(|| src.clone())
+}
+
+#[bench]
+pub fn clone_fat_val_100_and_clear(b: &mut Bencher) {
+    let src = fat_val_map(100);
+    b.iter(|| src.clone().clear())
+}
+
+#[bench]
+pub fn clone_fat_val_100_and_drain_all(b: &mut Bencher) {
+    let src = fat_val_map(100);
+    b.iter(|| src.clone().drain_filter(|_, _| true).count())
+}
+
+#[bench]
+pub fn clone_fat_val_100_and_drain_half(b: &mut Bencher) {
+    let src = fat_val_map(100);
+    b.iter(|| {
+        let mut map = src.clone();
+        assert_eq!(map.drain_filter(|i, _| i % 2 == 0).count(), 100 / 2);
+        assert_eq!(map.len(), 100 / 2);
+    })
+}
+
+#[bench]
+pub fn clone_fat_val_100_and_into_iter(b: &mut Bencher) {
+    let src = fat_val_map(100);
+    b.iter(|| src.clone().into_iter().count())
+}
+
+#[bench]
+pub fn clone_fat_val_100_and_pop_all(b: &mut Bencher) {
+    let src = fat_val_map(100);
+    b.iter(|| {
+        let mut map = src.clone();
+        while map.pop_first().is_some() {}
+        map
+    });
+}
+
+#[bench]
+pub fn clone_fat_val_100_and_remove_all(b: &mut Bencher) {
+    let src = fat_val_map(100);
+    b.iter(|| {
+        let mut map = src.clone();
+        while let Some(elt) = map.iter().map(|(&i, _)| i).next() {
+            let v = map.remove(&elt);
+            debug_assert!(v.is_some());
+        }
+        map
+    });
+}
+
+#[bench]
+pub fn clone_fat_val_100_and_remove_half(b: &mut Bencher) {
+    let src = fat_val_map(100);
+    b.iter(|| {
+        let mut map = src.clone();
+        for i in (0..100).step_by(2) {
+            let v = map.remove(&i);
+            debug_assert!(v.is_some());
+        }
+        assert_eq!(map.len(), 100 / 2);
+        map
+    })
+}
+
+#[bench]
+pub fn clone_fat_100(b: &mut Bencher) {
+    let src = fat_map(100);
+    b.iter(|| src.clone())
+}
+
+#[bench]
+pub fn clone_fat_100_and_clear(b: &mut Bencher) {
+    let src = fat_map(100);
+    b.iter(|| src.clone().clear())
+}
+
+#[bench]
+pub fn clone_fat_100_and_drain_all(b: &mut Bencher) {
+    let src = fat_map(100);
+    b.iter(|| src.clone().drain_filter(|_, _| true).count())
+}
+
+#[bench]
+pub fn clone_fat_100_and_drain_half(b: &mut Bencher) {
+    let src = fat_map(100);
+    b.iter(|| {
+        let mut map = src.clone();
+        assert_eq!(map.drain_filter(|i, _| i[0] % 2 == 0).count(), 100 / 2);
+        assert_eq!(map.len(), 100 / 2);
+    })
+}
+
+#[bench]
+pub fn clone_fat_100_and_into_iter(b: &mut Bencher) {
+    let src = fat_map(100);
+    b.iter(|| src.clone().into_iter().count())
+}
+
+#[bench]
+pub fn clone_fat_100_and_pop_all(b: &mut Bencher) {
+    let src = fat_map(100);
+    b.iter(|| {
+        let mut map = src.clone();
+        while map.pop_first().is_some() {}
+        map
+    });
+}
+
+#[bench]
+pub fn clone_fat_100_and_remove_all(b: &mut Bencher) {
+    let src = fat_map(100);
+    b.iter(|| {
+        let mut map = src.clone();
+        while let Some(elt) = map.iter().map(|(&i, _)| i).next() {
+            let v = map.remove(&elt);
+            debug_assert!(v.is_some());
+        }
+        map
+    });
+}
+
+#[bench]
+pub fn clone_fat_100_and_remove_half(b: &mut Bencher) {
+    let src = fat_map(100);
+    b.iter(|| {
+        let mut map = src.clone();
+        for i in (0..100).step_by(2) {
+            let v = map.remove(&[i; FAT]);
+            debug_assert!(v.is_some());
+        }
+        assert_eq!(map.len(), 100 / 2);
+        map
+    })
+}

library/alloc/benches/btree/set.rs

@@ -0,0 +1,224 @@
+use std::collections::BTreeSet;
+
+use rand::{thread_rng, Rng};
+use test::Bencher;
+
+fn random(n: usize) -> BTreeSet<usize> {
+    let mut rng = thread_rng();
+    let mut set = BTreeSet::new();
+    while set.len() < n {
+        set.insert(rng.gen());
+    }
+    assert_eq!(set.len(), n);
+    set
+}
+
+fn neg(n: usize) -> BTreeSet<i32> {
+    let set: BTreeSet<i32> = (-(n as i32)..=-1).collect();
+    assert_eq!(set.len(), n);
+    set
+}
+
+fn pos(n: usize) -> BTreeSet<i32> {
+    let set: BTreeSet<i32> = (1..=(n as i32)).collect();
+    assert_eq!(set.len(), n);
+    set
+}
+
+fn stagger(n1: usize, factor: usize) -> [BTreeSet<u32>; 2] {
+    let n2 = n1 * factor;
+    let mut sets = [BTreeSet::new(), BTreeSet::new()];
+    for i in 0..(n1 + n2) {
+        let b = i % (factor + 1) != 0;
+        sets[b as usize].insert(i as u32);
+    }
+    assert_eq!(sets[0].len(), n1);
+    assert_eq!(sets[1].len(), n2);
+    sets
+}
+
+macro_rules! set_bench {
+    ($name: ident, $set_func: ident, $result_func: ident, $sets: expr) => {
+        #[bench]
+        pub fn $name(b: &mut Bencher) {
+            // setup
+            let sets = $sets;
+
+            // measure
+            b.iter(|| sets[0].$set_func(&sets[1]).$result_func())
+        }
+    };
+}
+
+fn slim_set(n: usize) -> BTreeSet<usize> {
+    (0..n).collect::<BTreeSet<_>>()
+}
+
+#[bench]
+pub fn clone_100(b: &mut Bencher) {
+    let src = slim_set(100);
+    b.iter(|| src.clone())
+}
+
+#[bench]
+pub fn clone_100_and_clear(b: &mut Bencher) {
+    let src = slim_set(100);
+    b.iter(|| src.clone().clear())
+}
+
+#[bench]
+pub fn clone_100_and_drain_all(b: &mut Bencher) {
+    let src = slim_set(100);
+    b.iter(|| src.clone().drain_filter(|_| true).count())
+}
+
+#[bench]
+pub fn clone_100_and_drain_half(b: &mut Bencher) {
+    let src = slim_set(100);
+    b.iter(|| {
+        let mut set = src.clone();
+        assert_eq!(set.drain_filter(|i| i % 2 == 0).count(), 100 / 2);
+        assert_eq!(set.len(), 100 / 2);
+    })
+}
+
+#[bench]
+pub fn clone_100_and_into_iter(b: &mut Bencher) {
+    let src = slim_set(100);
+    b.iter(|| src.clone().into_iter().count())
+}
+
+#[bench]
+pub fn clone_100_and_pop_all(b: &mut Bencher) {
+    let src = slim_set(100);
+    b.iter(|| {
+        let mut set = src.clone();
+        while set.pop_first().is_some() {}
+        set
+    });
+}
+
+#[bench]
+pub fn clone_100_and_remove_all(b: &mut Bencher) {
+    let src = slim_set(100);
+    b.iter(|| {
+        let mut set = src.clone();
+        while let Some(elt) = set.iter().copied().next() {
+            let ok = set.remove(&elt);
+            debug_assert!(ok);
+        }
+        set
+    });
+}
+
+#[bench]
+pub fn clone_100_and_remove_half(b: &mut Bencher) {
+    let src = slim_set(100);
+    b.iter(|| {
+        let mut set = src.clone();
+        for i in (0..100).step_by(2) {
+            let ok = set.remove(&i);
+            debug_assert!(ok);
+        }
+        assert_eq!(set.len(), 100 / 2);
+        set
+    })
+}
+
+#[bench]
+pub fn clone_10k(b: &mut Bencher) {
+    let src = slim_set(10_000);
+    b.iter(|| src.clone())
+}
+
+#[bench]
+pub fn clone_10k_and_clear(b: &mut Bencher) {
+    let src = slim_set(10_000);
+    b.iter(|| src.clone().clear())
+}
+
+#[bench]
+pub fn clone_10k_and_drain_all(b: &mut Bencher) {
+    let src = slim_set(10_000);
+    b.iter(|| src.clone().drain_filter(|_| true).count())
+}
+
+#[bench]
+pub fn clone_10k_and_drain_half(b: &mut Bencher) {
+    let src = slim_set(10_000);
+    b.iter(|| {
+        let mut set = src.clone();
+        assert_eq!(set.drain_filter(|i| i % 2 == 0).count(), 10_000 / 2);
+        assert_eq!(set.len(), 10_000 / 2);
+    })
+}
+
+#[bench]
+pub fn clone_10k_and_into_iter(b: &mut Bencher) {
+    let src = slim_set(10_000);
+    b.iter(|| src.clone().into_iter().count())
+}
+
+#[bench]
+pub fn clone_10k_and_pop_all(b: &mut Bencher) {
+    let src = slim_set(10_000);
+    b.iter(|| {
+        let mut set = src.clone();
+        while set.pop_first().is_some() {}
+        set
+    });
+}
+
+#[bench]
+pub fn clone_10k_and_remove_all(b: &mut Bencher) {
+    let src = slim_set(10_000);
+    b.iter(|| {
+        let mut set = src.clone();
+        while let Some(elt) = set.iter().copied().next() {
+            let ok = set.remove(&elt);
+            debug_assert!(ok);
+        }
+        set
+    });
+}
+
+#[bench]
+pub fn clone_10k_and_remove_half(b: &mut Bencher) {
+    let src = slim_set(10_000);
+    b.iter(|| {
+        let mut set = src.clone();
+        for i in (0..10_000).step_by(2) {
+            let ok = set.remove(&i);
+            debug_assert!(ok);
+        }
+        assert_eq!(set.len(), 10_000 / 2);
+        set
+    })
+}
+
+set_bench! {intersection_100_neg_vs_100_pos, intersection, count, [neg(100), pos(100)]}
+set_bench! {intersection_100_neg_vs_10k_pos, intersection, count, [neg(100), pos(10_000)]}
+set_bench! {intersection_100_pos_vs_100_neg, intersection, count, [pos(100), neg(100)]}
+set_bench! {intersection_100_pos_vs_10k_neg, intersection, count, [pos(100), neg(10_000)]}
+set_bench! {intersection_10k_neg_vs_100_pos, intersection, count, [neg(10_000), pos(100)]}
+set_bench! {intersection_10k_neg_vs_10k_pos, intersection, count, [neg(10_000), pos(10_000)]}
+set_bench! {intersection_10k_pos_vs_100_neg, intersection, count, [pos(10_000), neg(100)]}
+set_bench! {intersection_10k_pos_vs_10k_neg, intersection, count, [pos(10_000), neg(10_000)]}
+set_bench! {intersection_random_100_vs_100, intersection, count, [random(100), random(100)]}
+set_bench! {intersection_random_100_vs_10k, intersection, count, [random(100), random(10_000)]}
+set_bench! {intersection_random_10k_vs_100, intersection, count, [random(10_000), random(100)]}
+set_bench! {intersection_random_10k_vs_10k, intersection, count, [random(10_000), random(10_000)]}
+set_bench! {intersection_staggered_100_vs_100, intersection, count, stagger(100, 1)}
+set_bench! {intersection_staggered_10k_vs_10k, intersection, count, stagger(10_000, 1)}
+set_bench! {intersection_staggered_100_vs_10k, intersection, count, stagger(100, 100)}
+set_bench! {difference_random_100_vs_100, difference, count, [random(100), random(100)]}
+set_bench! {difference_random_100_vs_10k, difference, count, [random(100), random(10_000)]}
+set_bench! {difference_random_10k_vs_100, difference, count, [random(10_000), random(100)]}
+set_bench! {difference_random_10k_vs_10k, difference, count, [random(10_000), random(10_000)]}
+set_bench! {difference_staggered_100_vs_100, difference, count, stagger(100, 1)}
+set_bench! {difference_staggered_10k_vs_10k, difference, count, stagger(10_000, 1)}
+set_bench! {difference_staggered_100_vs_10k, difference, count, stagger(100, 100)}
+set_bench! {is_subset_100_vs_100, is_subset, clone, [pos(100), pos(100)]}
+set_bench! {is_subset_100_vs_10k, is_subset, clone, [pos(100), pos(10_000)]}
+set_bench! {is_subset_10k_vs_100, is_subset, clone, [pos(10_000), pos(100)]}
+set_bench! {is_subset_10k_vs_10k, is_subset, clone, [pos(10_000), pos(10_000)]}

library/alloc/benches/vec.rs

@@ -0,0 +1,433 @@
+use std::iter::{repeat, FromIterator};
+use test::Bencher;
+
+#[bench]
+fn bench_new(b: &mut Bencher) {
+    b.iter(|| {
+        let v: Vec<u32> = Vec::new();
+        assert_eq!(v.len(), 0);
+        assert_eq!(v.capacity(), 0);
+    })
+}
+
+fn do_bench_with_capacity(b: &mut Bencher, src_len: usize) {
+    b.bytes = src_len as u64;
+
+    b.iter(|| {
+        let v: Vec<u32> = Vec::with_capacity(src_len);
+        assert_eq!(v.len(), 0);
+        assert_eq!(v.capacity(), src_len);
+    })
+}
+
+#[bench]
+fn bench_with_capacity_0000(b: &mut Bencher) {
+    do_bench_with_capacity(b, 0)
+}
+
+#[bench]
+fn bench_with_capacity_0010(b: &mut Bencher) {
+    do_bench_with_capacity(b, 10)
+}
+
+#[bench]
+fn bench_with_capacity_0100(b: &mut Bencher) {
+    do_bench_with_capacity(b, 100)
+}
+
+#[bench]
+fn bench_with_capacity_1000(b: &mut Bencher) {
+    do_bench_with_capacity(b, 1000)
+}
+
+fn do_bench_from_fn(b: &mut Bencher, src_len: usize) {
+    b.bytes = src_len as u64;
+
+    b.iter(|| {
+        let dst = (0..src_len).collect::<Vec<_>>();
+        assert_eq!(dst.len(), src_len);
+        assert!(dst.iter().enumerate().all(|(i, x)| i == *x));
+    })
+}
+
+#[bench]
+fn bench_from_fn_0000(b: &mut Bencher) {
+    do_bench_from_fn(b, 0)
+}
+
+#[bench]
+fn bench_from_fn_0010(b: &mut Bencher) {
+    do_bench_from_fn(b, 10)
+}
+
+#[bench]
+fn bench_from_fn_0100(b: &mut Bencher) {
+    do_bench_from_fn(b, 100)
+}
+
+#[bench]
+fn bench_from_fn_1000(b: &mut Bencher) {
+    do_bench_from_fn(b, 1000)
+}
+
+fn do_bench_from_elem(b: &mut Bencher, src_len: usize) {
+    b.bytes = src_len as u64;
+
+    b.iter(|| {
+        let dst: Vec<usize> = repeat(5).take(src_len).collect();
+        assert_eq!(dst.len(), src_len);
+        assert!(dst.iter().all(|x| *x == 5));
+    })
+}
+
+#[bench]
+fn bench_from_elem_0000(b: &mut Bencher) {
+    do_bench_from_elem(b, 0)
+}
+
+#[bench]
+fn bench_from_elem_0010(b: &mut Bencher) {
+    do_bench_from_elem(b, 10)
+}
+
+#[bench]
+fn bench_from_elem_0100(b: &mut Bencher) {
+    do_bench_from_elem(b, 100)
+}
+
+#[bench]
+fn bench_from_elem_1000(b: &mut Bencher) {
+    do_bench_from_elem(b, 1000)
+}
+
+fn do_bench_from_slice(b: &mut Bencher, src_len: usize) {
+    let src: Vec<_> = FromIterator::from_iter(0..src_len);
+
+    b.bytes = src_len as u64;
+
+    b.iter(|| {
+        let dst = src.clone()[..].to_vec();
+        assert_eq!(dst.len(), src_len);
+        assert!(dst.iter().enumerate().all(|(i, x)| i == *x));
+    });
+}
+
+#[bench]
+fn bench_from_slice_0000(b: &mut Bencher) {
+    do_bench_from_slice(b, 0)
+}
+
+#[bench]
+fn bench_from_slice_0010(b: &mut Bencher) {
+    do_bench_from_slice(b, 10)
+}
+
+#[bench]
+fn bench_from_slice_0100(b: &mut Bencher) {
+    do_bench_from_slice(b, 100)
+}
+
+#[bench]
+fn bench_from_slice_1000(b: &mut Bencher) {
+    do_bench_from_slice(b, 1000)
+}
+
+fn do_bench_from_iter(b: &mut Bencher, src_len: usize) {
+    let src: Vec<_> = FromIterator::from_iter(0..src_len);
+
+    b.bytes = src_len as u64;
+
+    b.iter(|| {
+        let dst: Vec<_> = FromIterator::from_iter(src.clone());
+        assert_eq!(dst.len(), src_len);
+        assert!(dst.iter().enumerate().all(|(i, x)| i == *x));
+    });
+}
+
+#[bench]
+fn bench_from_iter_0000(b: &mut Bencher) {
+    do_bench_from_iter(b, 0)
+}
+
+#[bench]
+fn bench_from_iter_0010(b: &mut Bencher) {
+    do_bench_from_iter(b, 10)
+}
+
+#[bench]
+fn bench_from_iter_0100(b: &mut Bencher) {
+    do_bench_from_iter(b, 100)
+}
+
+#[bench]
+fn bench_from_iter_1000(b: &mut Bencher) {
+    do_bench_from_iter(b, 1000)
+}
+
+fn do_bench_extend(b: &mut Bencher, dst_len: usize, src_len: usize) {
+    let dst: Vec<_> = FromIterator::from_iter(0..dst_len);
+    let src: Vec<_> = FromIterator::from_iter(dst_len..dst_len + src_len);
+
+    b.bytes = src_len as u64;
+
+    b.iter(|| {
+        let mut dst = dst.clone();
+        dst.extend(src.clone());
+        assert_eq!(dst.len(), dst_len + src_len);
+        assert!(dst.iter().enumerate().all(|(i, x)| i == *x));
+    });
+}
+
+#[bench]
+fn bench_extend_0000_0000(b: &mut Bencher) {
+    do_bench_extend(b, 0, 0)
+}
+
+#[bench]
+fn bench_extend_0000_0010(b: &mut Bencher) {
+    do_bench_extend(b, 0, 10)
+}
+
+#[bench]
+fn bench_extend_0000_0100(b: &mut Bencher) {
+    do_bench_extend(b, 0, 100)
+}
+
+#[bench]
+fn bench_extend_0000_1000(b: &mut Bencher) {
+    do_bench_extend(b, 0, 1000)
+}
+
+#[bench]
+fn bench_extend_0010_0010(b: &mut Bencher) {
+    do_bench_extend(b, 10, 10)
+}
+
+#[bench]
+fn bench_extend_0100_0100(b: &mut Bencher) {
+    do_bench_extend(b, 100, 100)
+}
+
+#[bench]
+fn bench_extend_1000_1000(b: &mut Bencher) {
+    do_bench_extend(b, 1000, 1000)
+}
+
+fn do_bench_extend_from_slice(b: &mut Bencher, dst_len: usize, src_len: usize) {
+    let dst: Vec<_> = FromIterator::from_iter(0..dst_len);
+    let src: Vec<_> = FromIterator::from_iter(dst_len..dst_len + src_len);
+
+    b.bytes = src_len as u64;
+
+    b.iter(|| {
+        let mut dst = dst.clone();
+        dst.extend_from_slice(&src);
+        assert_eq!(dst.len(), dst_len + src_len);
+        assert!(dst.iter().enumerate().all(|(i, x)| i == *x));
+    });
+}
+
+#[bench]
+fn bench_extend_from_slice_0000_0000(b: &mut Bencher) {
+    do_bench_extend_from_slice(b, 0, 0)
+}
+
+#[bench]
+fn bench_extend_from_slice_0000_0010(b: &mut Bencher) {
+    do_bench_extend_from_slice(b, 0, 10)
+}
+
+#[bench]
+fn bench_extend_from_slice_0000_0100(b: &mut Bencher) {
+    do_bench_extend_from_slice(b, 0, 100)
+}
+
+#[bench]
+fn bench_extend_from_slice_0000_1000(b: &mut Bencher) {
+    do_bench_extend_from_slice(b, 0, 1000)
+}
+
+#[bench]
+fn bench_extend_from_slice_0010_0010(b: &mut Bencher) {
+    do_bench_extend_from_slice(b, 10, 10)
+}
+
+#[bench]
+fn bench_extend_from_slice_0100_0100(b: &mut Bencher) {
+    do_bench_extend_from_slice(b, 100, 100)
+}
+
+#[bench]
+fn bench_extend_from_slice_1000_1000(b: &mut Bencher) {
+    do_bench_extend_from_slice(b, 1000, 1000)
+}
+
+fn do_bench_clone(b: &mut Bencher, src_len: usize) {
+    let src: Vec<usize> = FromIterator::from_iter(0..src_len);
+
+    b.bytes = src_len as u64;
+
+    b.iter(|| {
+        let dst = src.clone();
+        assert_eq!(dst.len(), src_len);
+        assert!(dst.iter().enumerate().all(|(i, x)| i == *x));
+    });
+}
+
+#[bench]
+fn bench_clone_0000(b: &mut Bencher) {
+    do_bench_clone(b, 0)
+}
+
+#[bench]
+fn bench_clone_0010(b: &mut Bencher) {
+    do_bench_clone(b, 10)
+}
+
+#[bench]
+fn bench_clone_0100(b: &mut Bencher) {
+    do_bench_clone(b, 100)
+}
+
+#[bench]
+fn bench_clone_1000(b: &mut Bencher) {
+    do_bench_clone(b, 1000)
+}
+
+fn do_bench_clone_from(b: &mut Bencher, times: usize, dst_len: usize, src_len: usize) {
+    let dst: Vec<_> = FromIterator::from_iter(0..src_len);
+    let src: Vec<_> = FromIterator::from_iter(dst_len..dst_len + src_len);
+
+    b.bytes = (times * src_len) as u64;
+
+    b.iter(|| {
+        let mut dst = dst.clone();
+
+        for _ in 0..times {
+            dst.clone_from(&src);
+
+            assert_eq!(dst.len(), src_len);
+            assert!(dst.iter().enumerate().all(|(i, x)| dst_len + i == *x));
+        }
+    });
+}
+
+#[bench]
+fn bench_clone_from_01_0000_0000(b: &mut Bencher) {
+    do_bench_clone_from(b, 1, 0, 0)
+}
+
+#[bench]
+fn bench_clone_from_01_0000_0010(b: &mut Bencher) {
+    do_bench_clone_from(b, 1, 0, 10)
+}
+
+#[bench]
+fn bench_clone_from_01_0000_0100(b: &mut Bencher) {
+    do_bench_clone_from(b, 1, 0, 100)
+}
+
+#[bench]
+fn bench_clone_from_01_0000_1000(b: &mut Bencher) {
+    do_bench_clone_from(b, 1, 0, 1000)
+}
+
+#[bench]
+fn bench_clone_from_01_0010_0010(b: &mut Bencher) {
+    do_bench_clone_from(b, 1, 10, 10)
+}
+
+#[bench]
+fn bench_clone_from_01_0100_0100(b: &mut Bencher) {
+    do_bench_clone_from(b, 1, 100, 100)
+}
+
+#[bench]
+fn bench_clone_from_01_1000_1000(b: &mut Bencher) {
+    do_bench_clone_from(b, 1, 1000, 1000)
+}
+
+#[bench]
+fn bench_clone_from_01_0010_0100(b: &mut Bencher) {
+    do_bench_clone_from(b, 1, 10, 100)
+}
+
+#[bench]
+fn bench_clone_from_01_0100_1000(b: &mut Bencher) {
+    do_bench_clone_from(b, 1, 100, 1000)
+}
+
+#[bench]
+fn bench_clone_from_01_0010_0000(b: &mut Bencher) {
+    do_bench_clone_from(b, 1, 10, 0)
+}
+
+#[bench]
+fn bench_clone_from_01_0100_0010(b: &mut Bencher) {
+    do_bench_clone_from(b, 1, 100, 10)
+}
+
+#[bench]
+fn bench_clone_from_01_1000_0100(b: &mut Bencher) {
+    do_bench_clone_from(b, 1, 1000, 100)
+}
+
+#[bench]
+fn bench_clone_from_10_0000_0000(b: &mut Bencher) {
+    do_bench_clone_from(b, 10, 0, 0)
+}
+
+#[bench]
+fn bench_clone_from_10_0000_0010(b: &mut Bencher) {
+    do_bench_clone_from(b, 10, 0, 10)
+}
+
+#[bench]
+fn bench_clone_from_10_0000_0100(b: &mut Bencher) {
+    do_bench_clone_from(b, 10, 0, 100)
+}
+
+#[bench]
+fn bench_clone_from_10_0000_1000(b: &mut Bencher) {
+    do_bench_clone_from(b, 10, 0, 1000)
+}
+
+#[bench]
+fn bench_clone_from_10_0010_0010(b: &mut Bencher) {
+    do_bench_clone_from(b, 10, 10, 10)
+}
+
+#[bench]
+fn bench_clone_from_10_0100_0100(b: &mut Bencher) {
+    do_bench_clone_from(b, 10, 100, 100)
+}
+
+#[bench]
+fn bench_clone_from_10_1000_1000(b: &mut Bencher) {
+    do_bench_clone_from(b, 10, 1000, 1000)
+}
+
+#[bench]
+fn bench_clone_from_10_0010_0100(b: &mut Bencher) {
+    do_bench_clone_from(b, 10, 10, 100)
+}
+
+#[bench]
+fn bench_clone_from_10_0100_1000(b: &mut Bencher) {
+    do_bench_clone_from(b, 10, 100, 1000)
+}
+
+#[bench]
+fn bench_clone_from_10_0010_0000(b: &mut Bencher) {
+    do_bench_clone_from(b, 10, 10, 0)
+}
+
+#[bench]
+fn bench_clone_from_10_0100_0010(b: &mut Bencher) {
+    do_bench_clone_from(b, 10, 100, 10)
+}
+
+#[bench]
+fn bench_clone_from_10_1000_0100(b: &mut Bencher) {
+    do_bench_clone_from(b, 10, 1000, 100)
+}

library/alloc/src/alloc.rs

@@ -0,0 +1,323 @@
+//! Memory allocation APIs
+
+#![stable(feature = "alloc_module", since = "1.28.0")]
+
+use core::intrinsics::{self, min_align_of_val, size_of_val};
+use core::ptr::{NonNull, Unique};
+
+#[stable(feature = "alloc_module", since = "1.28.0")]
+#[doc(inline)]
+pub use core::alloc::*;
+
+#[cfg(test)]
+mod tests;
+
+extern "Rust" {
+    // These are the magic symbols to call the global allocator.  rustc generates
+    // them from the `#[global_allocator]` attribute if there is one, or uses the
+    // default implementations in libstd (`__rdl_alloc` etc in `src/libstd/alloc.rs`)
+    // otherwise.
+    #[rustc_allocator]
+    #[rustc_allocator_nounwind]
+    fn __rust_alloc(size: usize, align: usize) -> *mut u8;
+    #[rustc_allocator_nounwind]
+    fn __rust_dealloc(ptr: *mut u8, size: usize, align: usize);
+    #[rustc_allocator_nounwind]
+    fn __rust_realloc(ptr: *mut u8, old_size: usize, align: usize, new_size: usize) -> *mut u8;
+    #[rustc_allocator_nounwind]
+    fn __rust_alloc_zeroed(size: usize, align: usize) -> *mut u8;
+}
+
+/// The global memory allocator.
+///
+/// This type implements the [`AllocRef`] trait by forwarding calls
+/// to the allocator registered with the `#[global_allocator]` attribute
+/// if there is one, or the `std` crate’s default.
+///
+/// Note: while this type is unstable, the functionality it provides can be
+/// accessed through the [free functions in `alloc`](index.html#functions).
+#[unstable(feature = "allocator_api", issue = "32838")]
+#[derive(Copy, Clone, Default, Debug)]
+pub struct Global;
+
+/// Allocate memory with the global allocator.
+///
+/// This function forwards calls to the [`GlobalAlloc::alloc`] method
+/// of the allocator registered with the `#[global_allocator]` attribute
+/// if there is one, or the `std` crate’s default.
+///
+/// This function is expected to be deprecated in favor of the `alloc` method
+/// of the [`Global`] type when it and the [`AllocRef`] trait become stable.
+///
+/// # Safety
+///
+/// See [`GlobalAlloc::alloc`].
+///
+/// # Examples
+///
+/// ```
+/// use std::alloc::{alloc, dealloc, Layout};
+///
+/// unsafe {
+///     let layout = Layout::new::<u16>();
+///     let ptr = alloc(layout);
+///
+///     *(ptr as *mut u16) = 42;
+///     assert_eq!(*(ptr as *mut u16), 42);
+///
+///     dealloc(ptr, layout);
+/// }
+/// ```
+#[stable(feature = "global_alloc", since = "1.28.0")]
+#[inline]
+pub unsafe fn alloc(layout: Layout) -> *mut u8 {
+    unsafe { __rust_alloc(layout.size(), layout.align()) }
+}
+
+/// Deallocate memory with the global allocator.
+///
+/// This function forwards calls to the [`GlobalAlloc::dealloc`] method
+/// of the allocator registered with the `#[global_allocator]` attribute
+/// if there is one, or the `std` crate’s default.
+///
+/// This function is expected to be deprecated in favor of the `dealloc` method
+/// of the [`Global`] type when it and the [`AllocRef`] trait become stable.
+///
+/// # Safety
+///
+/// See [`GlobalAlloc::dealloc`].
+#[stable(feature = "global_alloc", since = "1.28.0")]
+#[inline]
+pub unsafe fn dealloc(ptr: *mut u8, layout: Layout) {
+    unsafe { __rust_dealloc(ptr, layout.size(), layout.align()) }
+}
+
+/// Reallocate memory with the global allocator.
+///
+/// This function forwards calls to the [`GlobalAlloc::realloc`] method
+/// of the allocator registered with the `#[global_allocator]` attribute
+/// if there is one, or the `std` crate’s default.
+///
+/// This function is expected to be deprecated in favor of the `realloc` method
+/// of the [`Global`] type when it and the [`AllocRef`] trait become stable.
+///
+/// # Safety
+///
+/// See [`GlobalAlloc::realloc`].
+#[stable(feature = "global_alloc", since = "1.28.0")]
+#[inline]
+pub unsafe fn realloc(ptr: *mut u8, layout: Layout, new_size: usize) -> *mut u8 {
+    unsafe { __rust_realloc(ptr, layout.size(), layout.align(), new_size) }
+}
+
+/// Allocate zero-initialized memory with the global allocator.
+///
+/// This function forwards calls to the [`GlobalAlloc::alloc_zeroed`] method
+/// of the allocator registered with the `#[global_allocator]` attribute
+/// if there is one, or the `std` crate’s default.
+///
+/// This function is expected to be deprecated in favor of the `alloc_zeroed` method
+/// of the [`Global`] type when it and the [`AllocRef`] trait become stable.
+///
+/// # Safety
+///
+/// See [`GlobalAlloc::alloc_zeroed`].
+///
+/// # Examples
+///
+/// ```
+/// use std::alloc::{alloc_zeroed, dealloc, Layout};
+///
+/// unsafe {
+///     let layout = Layout::new::<u16>();
+///     let ptr = alloc_zeroed(layout);
+///
+///     assert_eq!(*(ptr as *mut u16), 0);
+///
+///     dealloc(ptr, layout);
+/// }
+/// ```
+#[stable(feature = "global_alloc", since = "1.28.0")]
+#[inline]
+pub unsafe fn alloc_zeroed(layout: Layout) -> *mut u8 {
+    unsafe { __rust_alloc_zeroed(layout.size(), layout.align()) }
+}
+
+impl Global {
+    #[inline]
+    fn alloc_impl(&mut self, layout: Layout, zeroed: bool) -> Result<NonNull<[u8]>, AllocErr> {
+        match layout.size() {
+            0 => Ok(NonNull::slice_from_raw_parts(layout.dangling(), 0)),
+            // SAFETY: `layout` is non-zero in size,
+            size => unsafe {
+                let raw_ptr = if zeroed { alloc_zeroed(layout) } else { alloc(layout) };
+                let ptr = NonNull::new(raw_ptr).ok_or(AllocErr)?;
+                Ok(NonNull::slice_from_raw_parts(ptr, size))
+            },
+        }
+    }
+
+    // Safety: Same as `AllocRef::grow`
+    #[inline]
+    unsafe fn grow_impl(
+        &mut self,
+        ptr: NonNull<u8>,
+        layout: Layout,
+        new_size: usize,
+        zeroed: bool,
+    ) -> Result<NonNull<[u8]>, AllocErr> {
+        debug_assert!(
+            new_size >= layout.size(),
+            "`new_size` must be greater than or equal to `layout.size()`"
+        );
+
+        match layout.size() {
+            // SAFETY: the caller must ensure that the `new_size` does not overflow.
+            // `layout.align()` comes from a `Layout` and is thus guaranteed to be valid for a Layout.
+            0 => unsafe {
+                let new_layout = Layout::from_size_align_unchecked(new_size, layout.align());
+                self.alloc_impl(new_layout, zeroed)
+            },
+
+            // SAFETY: `new_size` is non-zero as `old_size` is greater than or equal to `new_size`
+            // as required by safety conditions. Other conditions must be upheld by the caller
+            old_size => unsafe {
+                // `realloc` probably checks for `new_size >= size` or something similar.
+                intrinsics::assume(new_size >= layout.size());
+
+                let raw_ptr = realloc(ptr.as_ptr(), layout, new_size);
+                let ptr = NonNull::new(raw_ptr).ok_or(AllocErr)?;
+                if zeroed {
+                    raw_ptr.add(old_size).write_bytes(0, new_size - old_size);
+                }
+                Ok(NonNull::slice_from_raw_parts(ptr, new_size))
+            },
+        }
+    }
+}
+
+#[unstable(feature = "allocator_api", issue = "32838")]
+unsafe impl AllocRef for Global {
+    #[inline]
+    fn alloc(&mut self, layout: Layout) -> Result<NonNull<[u8]>, AllocErr> {
+        self.alloc_impl(layout, false)
+    }
+
+    #[inline]
+    fn alloc_zeroed(&mut self, layout: Layout) -> Result<NonNull<[u8]>, AllocErr> {
+        self.alloc_impl(layout, true)
+    }
+
+    #[inline]
+    unsafe fn dealloc(&mut self, ptr: NonNull<u8>, layout: Layout) {
+        if layout.size() != 0 {
+            // SAFETY: `layout` is non-zero in size,
+            // other conditions must be upheld by the caller
+            unsafe { dealloc(ptr.as_ptr(), layout) }
+        }
+    }
+
+    #[inline]
+    unsafe fn grow(
+        &mut self,
+        ptr: NonNull<u8>,
+        layout: Layout,
+        new_size: usize,
+    ) -> Result<NonNull<[u8]>, AllocErr> {
+        // SAFETY: all conditions must be upheld by the caller
+        unsafe { self.grow_impl(ptr, layout, new_size, false) }
+    }
+
+    #[inline]
+    unsafe fn grow_zeroed(
+        &mut self,
+        ptr: NonNull<u8>,
+        layout: Layout,
+        new_size: usize,
+    ) -> Result<NonNull<[u8]>, AllocErr> {
+        // SAFETY: all conditions must be upheld by the caller
+        unsafe { self.grow_impl(ptr, layout, new_size, true) }
+    }
+
+    #[inline]
+    unsafe fn shrink(
+        &mut self,
+        ptr: NonNull<u8>,
+        layout: Layout,
+        new_size: usize,
+    ) -> Result<NonNull<[u8]>, AllocErr> {
+        debug_assert!(
+            new_size <= layout.size(),
+            "`new_size` must be smaller than or equal to `layout.size()`"
+        );
+
+        match new_size {
+            // SAFETY: conditions must be upheld by the caller
+            0 => unsafe {
+                self.dealloc(ptr, layout);
+                Ok(NonNull::slice_from_raw_parts(layout.dangling(), 0))
+            },
+
+            // SAFETY: `new_size` is non-zero. Other conditions must be upheld by the caller
+            new_size => unsafe {
+                // `realloc` probably checks for `new_size <= size` or something similar.
+                intrinsics::assume(new_size <= layout.size());
+
+                let raw_ptr = realloc(ptr.as_ptr(), layout, new_size);
+                let ptr = NonNull::new(raw_ptr).ok_or(AllocErr)?;
+                Ok(NonNull::slice_from_raw_parts(ptr, new_size))
+            },
+        }
+    }
+}
+
+/// The allocator for unique pointers.
+// This function must not unwind. If it does, MIR codegen will fail.
+#[cfg(not(test))]
+#[lang = "exchange_malloc"]
+#[inline]
+unsafe fn exchange_malloc(size: usize, align: usize) -> *mut u8 {
+    let layout = unsafe { Layout::from_size_align_unchecked(size, align) };
+    match Global.alloc(layout) {
+        Ok(ptr) => ptr.as_non_null_ptr().as_ptr(),
+        Err(_) => handle_alloc_error(layout),
+    }
+}
+
+#[cfg_attr(not(test), lang = "box_free")]
+#[inline]
+// This signature has to be the same as `Box`, otherwise an ICE will happen.
+// When an additional parameter to `Box` is added (like `A: AllocRef`), this has to be added here as
+// well.
+// For example if `Box` is changed to  `struct Box<T: ?Sized, A: AllocRef>(Unique<T>, A)`,
+// this function has to be changed to `fn box_free<T: ?Sized, A: AllocRef>(Unique<T>, A)` as well.
+pub(crate) unsafe fn box_free<T: ?Sized>(ptr: Unique<T>) {
+    unsafe {
+        let size = size_of_val(ptr.as_ref());
+        let align = min_align_of_val(ptr.as_ref());
+        let layout = Layout::from_size_align_unchecked(size, align);
+        Global.dealloc(ptr.cast().into(), layout)
+    }
+}
+
+/// Abort on memory allocation error or failure.
+///
+/// Callers of memory allocation APIs wishing to abort computation
+/// in response to an allocation error are encouraged to call this function,
+/// rather than directly invoking `panic!` or similar.
+///
+/// The default behavior of this function is to print a message to standard error
+/// and abort the process.
+/// It can be replaced with [`set_alloc_error_hook`] and [`take_alloc_error_hook`].
+///
+/// [`set_alloc_error_hook`]: ../../std/alloc/fn.set_alloc_error_hook.html
+/// [`take_alloc_error_hook`]: ../../std/alloc/fn.take_alloc_error_hook.html
+#[stable(feature = "global_alloc", since = "1.28.0")]
+#[rustc_allocator_nounwind]
+pub fn handle_alloc_error(layout: Layout) -> ! {
+    extern "Rust" {
+        #[lang = "oom"]
+        fn oom_impl(layout: Layout) -> !;
+    }
+    unsafe { oom_impl(layout) }
+}

library/alloc/src/alloc/tests.rs

@@ -0,0 +1,30 @@
+use super::*;
+
+extern crate test;
+use crate::boxed::Box;
+use test::Bencher;
+
+#[test]
+fn allocate_zeroed() {
+    unsafe {
+        let layout = Layout::from_size_align(1024, 1).unwrap();
+        let ptr =
+            Global.alloc_zeroed(layout.clone()).unwrap_or_else(|_| handle_alloc_error(layout));
+
+        let mut i = ptr.as_non_null_ptr().as_ptr();
+        let end = i.add(layout.size());
+        while i < end {
+            assert_eq!(*i, 0);
+            i = i.offset(1);
+        }
+        Global.dealloc(ptr.as_non_null_ptr(), layout);
+    }
+}
+
+#[bench]
+#[cfg_attr(miri, ignore)] // isolated Miri does not support benchmarks
+fn alloc_owned_small(b: &mut Bencher) {
+    b.iter(|| {
+        let _: Box<_> = box 10;
+    })
+}

library/alloc/src/collections/binary_heap.rs

@@ -1,9 +1,9 @@
 //! A priority queue implemented with a binary heap.
 //!
-//! Insertion and popping the largest element have `O(log(n))` time complexity.
+//! Insertion and popping the largest element have *O*(log(*n*)) time complexity.
-//! Checking the largest element is `O(1)`. Converting a vector to a binary heap
+//! Checking the largest element is *O*(1). Converting a vector to a binary heap
-//! can be done in-place, and has `O(n)` complexity. A binary heap can also be
+//! can be done in-place, and has *O*(*n*) complexity. A binary heap can also be
-//! converted to a sorted vector in-place, allowing it to be used for an `O(n * log(n))`
+//! converted to a sorted vector in-place, allowing it to be used for an *O*(*n* \* log(*n*))
 //! in-place heapsort.
 //!
 //! # Examples
@@ -12,9 +12,9 @@
 //! to solve the [shortest path problem][sssp] on a [directed graph][dir_graph].
 //! It shows how to use [`BinaryHeap`] with custom types.
 //!
-//! [dijkstra]: http://en.wikipedia.org/wiki/Dijkstra%27s_algorithm
+//! [dijkstra]: https://en.wikipedia.org/wiki/Dijkstra%27s_algorithm
-//! [sssp]: http://en.wikipedia.org/wiki/Shortest_path_problem
+//! [sssp]: https://en.wikipedia.org/wiki/Shortest_path_problem
-//! [dir_graph]: http://en.wikipedia.org/wiki/Directed_graph
+//! [dir_graph]: https://en.wikipedia.org/wiki/Directed_graph
 //! [`BinaryHeap`]: struct.BinaryHeap.html
 //!
 //! ```
@@ -235,7 +235,7 @@ use super::SpecExtend;
 ///
 /// | [push] | [pop]     | [peek]/[peek\_mut] |
 /// |--------|-----------|--------------------|
-/// | O(1)~  | O(log(n)) | O(1)               |
+/// | O(1)~  | *O*(log(*n*)) | *O*(1)               |
 ///
 /// The value for `push` is an expected cost; the method documentation gives a
 /// more detailed analysis.
@@ -398,7 +398,7 @@ impl<T: Ord> BinaryHeap<T> {
     ///
     /// # Time complexity
     ///
-    /// Cost is `O(1)` in the worst case.
+    /// Cost is *O*(1) in the worst case.
     #[stable(feature = "binary_heap_peek_mut", since = "1.12.0")]
     pub fn peek_mut(&mut self) -> Option<PeekMut<'_, T>> {
         if self.is_empty() { None } else { Some(PeekMut { heap: self, sift: true }) }
@@ -422,7 +422,7 @@ impl<T: Ord> BinaryHeap<T> {
     ///
     /// # Time complexity
     ///
-    /// The worst case cost of `pop` on a heap containing *n* elements is `O(log(n))`.
+    /// The worst case cost of `pop` on a heap containing *n* elements is *O*(log(*n*)).
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn pop(&mut self) -> Option<T> {
         self.data.pop().map(|mut item| {
@@ -455,15 +455,15 @@ impl<T: Ord> BinaryHeap<T> {
     ///
     /// The expected cost of `push`, averaged over every possible ordering of
     /// the elements being pushed, and over a sufficiently large number of
-    /// pushes, is `O(1)`. This is the most meaningful cost metric when pushing
+    /// pushes, is *O*(1). This is the most meaningful cost metric when pushing
     /// elements that are *not* already in any sorted pattern.
     ///
     /// The time complexity degrades if elements are pushed in predominantly
     /// ascending order. In the worst case, elements are pushed in ascending
-    /// sorted order and the amortized cost per push is `O(log(n))` against a heap
+    /// sorted order and the amortized cost per push is *O*(log(*n*)) against a heap
     /// containing *n* elements.
     ///
-    /// The worst case cost of a *single* call to `push` is `O(n)`. The worst case
+    /// The worst case cost of a *single* call to `push` is *O*(*n*). The worst case
     /// occurs when capacity is exhausted and needs a resize. The resize cost
     /// has been amortized in the previous figures.
     #[stable(feature = "rust1", since = "1.0.0")]
@@ -643,7 +643,7 @@ impl<T: Ord> BinaryHeap<T> {
     /// The remaining elements will be removed on drop in heap order.
     ///
     /// Note:
-    /// * `.drain_sorted()` is `O(n * log(n))`; much slower than `.drain()`.
+    /// * `.drain_sorted()` is *O*(*n* \* log(*n*)); much slower than `.drain()`.
     ///   You should use the latter for most cases.
     ///
     /// # Examples
@@ -756,7 +756,7 @@ impl<T> BinaryHeap<T> {
     ///
     /// # Time complexity
     ///
-    /// Cost is `O(1)` in the worst case.
+    /// Cost is *O*(1) in the worst case.
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn peek(&self) -> Option<&T> {
         self.data.get(0)
@@ -1312,7 +1312,7 @@ unsafe impl<T: Ord> TrustedLen for DrainSorted<'_, T> {}
 impl<T: Ord> From<Vec<T>> for BinaryHeap<T> {
     /// Converts a `Vec<T>` into a `BinaryHeap<T>`.
     ///
-    /// This conversion happens in-place, and has `O(n)` time complexity.
+    /// This conversion happens in-place, and has *O*(*n*) time complexity.
     fn from(vec: Vec<T>) -> BinaryHeap<T> {
         let mut heap = BinaryHeap { data: vec };
         heap.rebuild();

library/alloc/src/collections/btree/mod.rs

@@ -0,0 +1,54 @@
+pub mod map;
+mod navigate;
+mod node;
+mod search;
+pub mod set;
+
+#[doc(hidden)]
+trait Recover<Q: ?Sized> {
+    type Key;
+
+    fn get(&self, key: &Q) -> Option<&Self::Key>;
+    fn take(&mut self, key: &Q) -> Option<Self::Key>;
+    fn replace(&mut self, key: Self::Key) -> Option<Self::Key>;
+}
+
+#[inline(always)]
+pub unsafe fn unwrap_unchecked<T>(val: Option<T>) -> T {
+    val.unwrap_or_else(|| {
+        if cfg!(debug_assertions) {
+            panic!("'unchecked' unwrap on None in BTreeMap");
+        } else {
+            unsafe {
+                core::intrinsics::unreachable();
+            }
+        }
+    })
+}
+
+#[cfg(test)]
+/// XorShiftRng
+struct DeterministicRng {
+    x: u32,
+    y: u32,
+    z: u32,
+    w: u32,
+}
+
+#[cfg(test)]
+impl DeterministicRng {
+    fn new() -> Self {
+        DeterministicRng { x: 0x193a6754, y: 0xa8a7d469, z: 0x97830e05, w: 0x113ba7bb }
+    }
+
+    fn next(&mut self) -> u32 {
+        let x = self.x;
+        let t = x ^ (x << 11);
+        self.x = self.y;
+        self.y = self.z;
+        self.z = self.w;
+        let w_ = self.w;
+        self.w = w_ ^ (w_ >> 19) ^ (t ^ (t >> 8));
+        self.w
+    }
+}

library/alloc/src/collections/btree/navigate.rs

@@ -0,0 +1,335 @@
+use core::intrinsics;
+use core::mem;
+use core::ptr;
+
+use super::node::{marker, ForceResult::*, Handle, NodeRef};
+use super::unwrap_unchecked;
+
+impl<BorrowType, K, V> Handle<NodeRef<BorrowType, K, V, marker::Leaf>, marker::Edge> {
+    /// Given a leaf edge handle, returns [`Result::Ok`] with a handle to the neighboring KV
+    /// on the right side, which is either in the same leaf node or in an ancestor node.
+    /// If the leaf edge is the last one in the tree, returns [`Result::Err`] with the root node.
+    pub fn next_kv(
+        self,
+    ) -> Result<
+        Handle<NodeRef<BorrowType, K, V, marker::LeafOrInternal>, marker::KV>,
+        NodeRef<BorrowType, K, V, marker::LeafOrInternal>,
+    > {
+        let mut edge = self.forget_node_type();
+        loop {
+            edge = match edge.right_kv() {
+                Ok(internal_kv) => return Ok(internal_kv),
+                Err(last_edge) => match last_edge.into_node().ascend() {
+                    Ok(parent_edge) => parent_edge.forget_node_type(),
+                    Err(root) => return Err(root),
+                },
+            }
+        }
+    }
+
+    /// Given a leaf edge handle, returns [`Result::Ok`] with a handle to the neighboring KV
+    /// on the left side, which is either in the same leaf node or in an ancestor node.
+    /// If the leaf edge is the first one in the tree, returns [`Result::Err`] with the root node.
+    pub fn next_back_kv(
+        self,
+    ) -> Result<
+        Handle<NodeRef<BorrowType, K, V, marker::LeafOrInternal>, marker::KV>,
+        NodeRef<BorrowType, K, V, marker::LeafOrInternal>,
+    > {
+        let mut edge = self.forget_node_type();
+        loop {
+            edge = match edge.left_kv() {
+                Ok(internal_kv) => return Ok(internal_kv),
+                Err(last_edge) => match last_edge.into_node().ascend() {
+                    Ok(parent_edge) => parent_edge.forget_node_type(),
+                    Err(root) => return Err(root),
+                },
+            }
+        }
+    }
+}
+
+impl<BorrowType, K, V> Handle<NodeRef<BorrowType, K, V, marker::Internal>, marker::Edge> {
+    /// Given an internal edge handle, returns [`Result::Ok`] with a handle to the neighboring KV
+    /// on the right side, which is either in the same internal node or in an ancestor node.
+    /// If the internal edge is the last one in the tree, returns [`Result::Err`] with the root node.
+    pub fn next_kv(
+        self,
+    ) -> Result<
+        Handle<NodeRef<BorrowType, K, V, marker::Internal>, marker::KV>,
+        NodeRef<BorrowType, K, V, marker::Internal>,
+    > {
+        let mut edge = self;
+        loop {
+            edge = match edge.right_kv() {
+                Ok(internal_kv) => return Ok(internal_kv),
+                Err(last_edge) => match last_edge.into_node().ascend() {
+                    Ok(parent_edge) => parent_edge,
+                    Err(root) => return Err(root),
+                },
+            }
+        }
+    }
+}
+
+macro_rules! def_next_kv_uncheched_dealloc {
+    { unsafe fn $name:ident : $adjacent_kv:ident } => {
+        /// Given a leaf edge handle into an owned tree, returns a handle to the next KV,
+        /// while deallocating any node left behind.
+        /// Unsafe for two reasons:
+        /// - The caller must ensure that the leaf edge is not the last one in the tree.
+        /// - The node pointed at by the given handle, and its ancestors, may be deallocated,
+        ///   while the reference to those nodes in the surviving ancestors is left dangling;
+        ///   thus using the returned handle to navigate further is dangerous.
+        unsafe fn $name <K, V>(
+            leaf_edge: Handle<NodeRef<marker::Owned, K, V, marker::Leaf>, marker::Edge>,
+        ) -> Handle<NodeRef<marker::Owned, K, V, marker::LeafOrInternal>, marker::KV> {
+            let mut edge = leaf_edge.forget_node_type();
+            loop {
+                edge = match edge.$adjacent_kv() {
+                    Ok(internal_kv) => return internal_kv,
+                    Err(last_edge) => {
+                        unsafe {
+                            let parent_edge = last_edge.into_node().deallocate_and_ascend();
+                            unwrap_unchecked(parent_edge).forget_node_type()
+                        }
+                    }
+                }
+            }
+        }
+    };
+}
+
+def_next_kv_uncheched_dealloc! {unsafe fn next_kv_unchecked_dealloc: right_kv}
+def_next_kv_uncheched_dealloc! {unsafe fn next_back_kv_unchecked_dealloc: left_kv}
+
+/// This replaces the value behind the `v` unique reference by calling the
+/// relevant function, and returns a result obtained along the way.
+///
+/// If a panic occurs in the `change` closure, the entire process will be aborted.
+#[inline]
+fn replace<T, R>(v: &mut T, change: impl FnOnce(T) -> (T, R)) -> R {
+    struct PanicGuard;
+    impl Drop for PanicGuard {
+        fn drop(&mut self) {
+            intrinsics::abort()
+        }
+    }
+    let guard = PanicGuard;
+    let value = unsafe { ptr::read(v) };
+    let (new_value, ret) = change(value);
+    unsafe {
+        ptr::write(v, new_value);
+    }
+    mem::forget(guard);
+    ret
+}
+
+impl<'a, K, V> Handle<NodeRef<marker::Immut<'a>, K, V, marker::Leaf>, marker::Edge> {
+    /// Moves the leaf edge handle to the next leaf edge and returns references to the
+    /// key and value in between.
+    /// Unsafe because the caller must ensure that the leaf edge is not the last one in the tree.
+    pub unsafe fn next_unchecked(&mut self) -> (&'a K, &'a V) {
+        replace(self, |leaf_edge| {
+            let kv = leaf_edge.next_kv();
+            let kv = unsafe { unwrap_unchecked(kv.ok()) };
+            (kv.next_leaf_edge(), kv.into_kv())
+        })
+    }
+
+    /// Moves the leaf edge handle to the previous leaf edge and returns references to the
+    /// key and value in between.
+    /// Unsafe because the caller must ensure that the leaf edge is not the first one in the tree.
+    pub unsafe fn next_back_unchecked(&mut self) -> (&'a K, &'a V) {
+        replace(self, |leaf_edge| {
+            let kv = leaf_edge.next_back_kv();
+            let kv = unsafe { unwrap_unchecked(kv.ok()) };
+            (kv.next_back_leaf_edge(), kv.into_kv())
+        })
+    }
+}
+
+impl<'a, K, V> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::Edge> {
+    /// Moves the leaf edge handle to the next leaf edge and returns references to the
+    /// key and value in between.
+    /// Unsafe for two reasons:
+    /// - The caller must ensure that the leaf edge is not the last one in the tree.
+    /// - Using the updated handle may well invalidate the returned references.
+    pub unsafe fn next_unchecked(&mut self) -> (&'a mut K, &'a mut V) {
+        let kv = replace(self, |leaf_edge| {
+            let kv = leaf_edge.next_kv();
+            let kv = unsafe { unwrap_unchecked(kv.ok()) };
+            (unsafe { ptr::read(&kv) }.next_leaf_edge(), kv)
+        });
+        // Doing the descend (and perhaps another move) invalidates the references
+        // returned by `into_kv_mut`, so we have to do this last.
+        kv.into_kv_mut()
+    }
+
+    /// Moves the leaf edge handle to the previous leaf and returns references to the
+    /// key and value in between.
+    /// Unsafe for two reasons:
+    /// - The caller must ensure that the leaf edge is not the first one in the tree.
+    /// - Using the updated handle may well invalidate the returned references.
+    pub unsafe fn next_back_unchecked(&mut self) -> (&'a mut K, &'a mut V) {
+        let kv = replace(self, |leaf_edge| {
+            let kv = leaf_edge.next_back_kv();
+            let kv = unsafe { unwrap_unchecked(kv.ok()) };
+            (unsafe { ptr::read(&kv) }.next_back_leaf_edge(), kv)
+        });
+        // Doing the descend (and perhaps another move) invalidates the references
+        // returned by `into_kv_mut`, so we have to do this last.
+        kv.into_kv_mut()
+    }
+}
+
+impl<K, V> Handle<NodeRef<marker::Owned, K, V, marker::Leaf>, marker::Edge> {
+    /// Moves the leaf edge handle to the next leaf edge and returns the key and value
+    /// in between, while deallocating any node left behind.
+    /// Unsafe for two reasons:
+    /// - The caller must ensure that the leaf edge is not the last one in the tree
+    ///   and is not a handle previously resulting from counterpart `next_back_unchecked`.
+    /// - Further use of the updated leaf edge handle is very dangerous. In particular,
+    ///   if the leaf edge is the last edge of a node, that node and possibly ancestors
+    ///   will be deallocated, while the reference to those nodes in the surviving ancestor
+    ///   is left dangling.
+    ///   The only safe way to proceed with the updated handle is to compare it, drop it,
+    ///   call this method again subject to both preconditions listed in the first point,
+    ///   or call counterpart `next_back_unchecked` subject to its preconditions.
+    pub unsafe fn next_unchecked(&mut self) -> (K, V) {
+        replace(self, |leaf_edge| {
+            let kv = unsafe { next_kv_unchecked_dealloc(leaf_edge) };
+            let k = unsafe { ptr::read(kv.reborrow().into_kv().0) };
+            let v = unsafe { ptr::read(kv.reborrow().into_kv().1) };
+            (kv.next_leaf_edge(), (k, v))
+        })
+    }
+
+    /// Moves the leaf edge handle to the previous leaf edge and returns the key
+    /// and value in between, while deallocating any node left behind.
+    /// Unsafe for two reasons:
+    /// - The caller must ensure that the leaf edge is not the first one in the tree
+    ///   and is not a handle previously resulting from counterpart `next_unchecked`.
+    /// - Further use of the updated leaf edge handle is very dangerous. In particular,
+    ///   if the leaf edge is the first edge of a node, that node and possibly ancestors
+    ///   will be deallocated, while the reference to those nodes in the surviving ancestor
+    ///   is left dangling.
+    ///   The only safe way to proceed with the updated handle is to compare it, drop it,
+    ///   call this method again subject to both preconditions listed in the first point,
+    ///   or call counterpart `next_unchecked` subject to its preconditions.
+    pub unsafe fn next_back_unchecked(&mut self) -> (K, V) {
+        replace(self, |leaf_edge| {
+            let kv = unsafe { next_back_kv_unchecked_dealloc(leaf_edge) };
+            let k = unsafe { ptr::read(kv.reborrow().into_kv().0) };
+            let v = unsafe { ptr::read(kv.reborrow().into_kv().1) };
+            (kv.next_back_leaf_edge(), (k, v))
+        })
+    }
+}
+
+impl<BorrowType, K, V> NodeRef<BorrowType, K, V, marker::LeafOrInternal> {
+    /// Returns the leftmost leaf edge in or underneath a node - in other words, the edge
+    /// you need first when navigating forward (or last when navigating backward).
+    #[inline]
+    pub fn first_leaf_edge(self) -> Handle<NodeRef<BorrowType, K, V, marker::Leaf>, marker::Edge> {
+        let mut node = self;
+        loop {
+            match node.force() {
+                Leaf(leaf) => return leaf.first_edge(),
+                Internal(internal) => node = internal.first_edge().descend(),
+            }
+        }
+    }
+
+    /// Returns the rightmost leaf edge in or underneath a node - in other words, the edge
+    /// you need last when navigating forward (or first when navigating backward).
+    #[inline]
+    pub fn last_leaf_edge(self) -> Handle<NodeRef<BorrowType, K, V, marker::Leaf>, marker::Edge> {
+        let mut node = self;
+        loop {
+            match node.force() {
+                Leaf(leaf) => return leaf.last_edge(),
+                Internal(internal) => node = internal.last_edge().descend(),
+            }
+        }
+    }
+}
+
+pub enum Position<BorrowType, K, V> {
+    Leaf(NodeRef<BorrowType, K, V, marker::Leaf>),
+    Internal(NodeRef<BorrowType, K, V, marker::Internal>),
+    InternalKV(Handle<NodeRef<BorrowType, K, V, marker::Internal>, marker::KV>),
+}
+
+impl<'a, K: 'a, V: 'a> NodeRef<marker::Immut<'a>, K, V, marker::LeafOrInternal> {
+    /// Visits leaf nodes and internal KVs in order of ascending keys, and also
+    /// visits internal nodes as a whole in a depth first order, meaning that
+    /// internal nodes precede their individual KVs and their child nodes.
+    pub fn visit_nodes_in_order<F>(self, mut visit: F)
+    where
+        F: FnMut(Position<marker::Immut<'a>, K, V>),
+    {
+        match self.force() {
+            Leaf(leaf) => visit(Position::Leaf(leaf)),
+            Internal(internal) => {
+                visit(Position::Internal(internal));
+                let mut edge = internal.first_edge();
+                loop {
+                    edge = match edge.descend().force() {
+                        Leaf(leaf) => {
+                            visit(Position::Leaf(leaf));
+                            match edge.next_kv() {
+                                Ok(kv) => {
+                                    visit(Position::InternalKV(kv));
+                                    kv.right_edge()
+                                }
+                                Err(_) => return,
+                            }
+                        }
+                        Internal(internal) => {
+                            visit(Position::Internal(internal));
+                            internal.first_edge()
+                        }
+                    }
+                }
+            }
+        }
+    }
+
+    /// Calculates the number of elements in a (sub)tree.
+    pub fn calc_length(self) -> usize {
+        let mut result = 0;
+        self.visit_nodes_in_order(|pos| match pos {
+            Position::Leaf(node) => result += node.len(),
+            Position::Internal(node) => result += node.len(),
+            Position::InternalKV(_) => (),
+        });
+        result
+    }
+}
+
+impl<BorrowType, K, V> Handle<NodeRef<BorrowType, K, V, marker::LeafOrInternal>, marker::KV> {
+    /// Returns the leaf edge closest to a KV for forward navigation.
+    pub fn next_leaf_edge(self) -> Handle<NodeRef<BorrowType, K, V, marker::Leaf>, marker::Edge> {
+        match self.force() {
+            Leaf(leaf_kv) => leaf_kv.right_edge(),
+            Internal(internal_kv) => {
+                let next_internal_edge = internal_kv.right_edge();
+                next_internal_edge.descend().first_leaf_edge()
+            }
+        }
+    }
+
+    /// Returns the leaf edge closest to a KV for backward navigation.
+    pub fn next_back_leaf_edge(
+        self,
+    ) -> Handle<NodeRef<BorrowType, K, V, marker::Leaf>, marker::Edge> {
+        match self.force() {
+            Leaf(leaf_kv) => leaf_kv.left_edge(),
+            Internal(internal_kv) => {
+                let next_internal_edge = internal_kv.left_edge();
+                next_internal_edge.descend().last_leaf_edge()
+            }
+        }
+    }
+}

library/alloc/src/collections/btree/node.rs

@@ -43,6 +43,9 @@ use crate::boxed::Box;
 const B: usize = 6;
 pub const MIN_LEN: usize = B - 1;
 pub const CAPACITY: usize = 2 * B - 1;
+const KV_IDX_CENTER: usize = B - 1;
+const EDGE_IDX_LEFT_OF_CENTER: usize = B - 1;
+const EDGE_IDX_RIGHT_OF_CENTER: usize = B;
 
 /// The underlying representation of leaf nodes.
 #[repr(C)]
@@ -94,7 +97,8 @@ struct InternalNode<K, V> {
     data: LeafNode<K, V>,
 
     /// The pointers to the children of this node. `len + 1` of these are considered
-    /// initialized and valid.
+    /// initialized and valid. Although during the process of `into_iter` or `drop`,
+    /// some pointers are dangling while others still need to be traversed.
     edges: [MaybeUninit<BoxedNode<K, V>>; 2 * B],
 }
 
@@ -152,12 +156,18 @@ unsafe impl<K: Sync, V: Sync> Sync for Root<K, V> {}
 unsafe impl<K: Send, V: Send> Send for Root<K, V> {}
 
 impl<K, V> Root<K, V> {
+    /// Returns the number of levels below the root.
+    pub fn height(&self) -> usize {
+        self.height
+    }
+
     /// Returns a new owned tree, with its own root node that is initially empty.
     pub fn new_leaf() -> Self {
         Root { node: BoxedNode::from_leaf(Box::new(unsafe { LeafNode::new() })), height: 0 }
     }
 
-    pub fn as_ref(&self) -> NodeRef<marker::Immut<'_>, K, V, marker::LeafOrInternal> {
+    /// Borrows and returns an immutable reference to the node owned by the root.
+    pub fn node_as_ref(&self) -> NodeRef<marker::Immut<'_>, K, V, marker::LeafOrInternal> {
         NodeRef {
             height: self.height,
             node: self.node.as_ptr(),
@@ -166,7 +176,8 @@ impl<K, V> Root<K, V> {
         }
     }
 
-    pub fn as_mut(&mut self) -> NodeRef<marker::Mut<'_>, K, V, marker::LeafOrInternal> {
+    /// Borrows and returns a mutable reference to the node owned by the root.
+    pub fn node_as_mut(&mut self) -> NodeRef<marker::Mut<'_>, K, V, marker::LeafOrInternal> {
         NodeRef {
             height: self.height,
             node: self.node.as_ptr(),
@@ -185,8 +196,9 @@ impl<K, V> Root<K, V> {
     }
 
     /// Adds a new internal node with a single edge, pointing to the previous root, and make that
-    /// new node the root. This increases the height by 1 and is the opposite of `pop_level`.
+    /// new node the root. This increases the height by 1 and is the opposite of
-    pub fn push_level(&mut self) -> NodeRef<marker::Mut<'_>, K, V, marker::Internal> {
+    /// `pop_internal_level`.
+    pub fn push_internal_level(&mut self) -> NodeRef<marker::Mut<'_>, K, V, marker::Internal> {
         let mut new_node = Box::new(unsafe { InternalNode::new() });
         new_node.edges[0].write(unsafe { BoxedNode::from_ptr(self.node.as_ptr()) });
 
@@ -207,23 +219,24 @@ impl<K, V> Root<K, V> {
         ret
     }
 
-    /// Removes the root node, using its first child as the new root. This cannot be called when
+    /// Removes the internal root node, using its first child as the new root.
-    /// the tree consists only of a leaf node. As it is intended only to be called when the root
+    /// As it is intended only to be called when the root has only one child,
-    /// has only one edge, no cleanup is done on any of the other children of the root.
+    /// no cleanup is done on any of the other children of the root.
-    /// This decreases the height by 1 and is the opposite of `push_level`.
+    /// This decreases the height by 1 and is the opposite of `push_internal_level`.
-    pub fn pop_level(&mut self) {
+    /// Panics if there is no internal level, i.e. if the root is a leaf.
+    pub fn pop_internal_level(&mut self) {
         assert!(self.height > 0);
 
         let top = self.node.ptr;
 
         self.node = unsafe {
             BoxedNode::from_ptr(
-                self.as_mut().cast_unchecked::<marker::Internal>().first_edge().descend().node,
+                self.node_as_mut().cast_unchecked::<marker::Internal>().first_edge().descend().node,
             )
         };
         self.height -= 1;
         unsafe {
-            (*self.as_mut().as_leaf_mut()).parent = ptr::null();
+            (*self.node_as_mut().as_leaf_mut()).parent = ptr::null();
         }
 
         unsafe {
@@ -299,12 +312,6 @@ impl<BorrowType, K, V, Type> NodeRef<BorrowType, K, V, Type> {
         self.height
     }
 
-    /// Removes any static information about whether this node is a `Leaf` or an
-    /// `Internal` node.
-    pub fn forget_type(self) -> NodeRef<BorrowType, K, V, marker::LeafOrInternal> {
-        NodeRef { height: self.height, node: self.node, root: self.root, _marker: PhantomData }
-    }
-
     /// Temporarily takes out another, immutable reference to the same node.
     fn reborrow(&self) -> NodeRef<marker::Immut<'_>, K, V, Type> {
         NodeRef { height: self.height, node: self.node, root: self.root, _marker: PhantomData }
@@ -408,8 +415,8 @@ impl<K, V> NodeRef<marker::Owned, K, V, marker::LeafOrInternal> {
 
 impl<'a, K, V, Type> NodeRef<marker::Mut<'a>, K, V, Type> {
     /// Unsafely asserts to the compiler some static information about whether this
-    /// node is a `Leaf`.
+    /// node is a `Leaf` or an `Internal`.
-    unsafe fn cast_unchecked<NewType>(&mut self) -> NodeRef<marker::Mut<'_>, K, V, NewType> {
+    unsafe fn cast_unchecked<NewType>(self) -> NodeRef<marker::Mut<'a>, K, V, NewType> {
         NodeRef { height: self.height, node: self.node, root: self.root, _marker: PhantomData }
     }
 
@@ -460,12 +467,6 @@ impl<'a, K: 'a, V: 'a, Type> NodeRef<marker::Immut<'a>, K, V, Type> {
     fn into_val_slice(self) -> &'a [V] {
         unsafe { slice::from_raw_parts(MaybeUninit::first_ptr(&self.as_leaf().vals), self.len()) }
     }
-
-    fn into_slices(self) -> (&'a [K], &'a [V]) {
-        // SAFETY: equivalent to reborrow() except not requiring Type: 'a
-        let k = unsafe { ptr::read(&self) };
-        (k.into_key_slice(), self.into_val_slice())
-    }
 }
 
 impl<'a, K: 'a, V: 'a, Type> NodeRef<marker::Mut<'a>, K, V, Type> {
@@ -515,7 +516,7 @@ impl<'a, K: 'a, V: 'a, Type> NodeRef<marker::Mut<'a>, K, V, Type> {
 }
 
 impl<'a, K, V> NodeRef<marker::Mut<'a>, K, V, marker::Leaf> {
-    /// Adds a key/value pair the end of the node.
+    /// Adds a key/value pair to the end of the node.
     pub fn push(&mut self, key: K, val: V) {
         assert!(self.len() < CAPACITY);
 
@@ -602,8 +603,10 @@ impl<'a, K, V> NodeRef<marker::Mut<'a>, K, V, marker::Internal> {
 }
 
 impl<'a, K, V> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
-    /// Removes a key/value pair from the end of this node. If this is an internal node,
+    /// Removes a key/value pair from the end of this node and returns the pair.
-    /// also removes the edge that was to the right of that pair.
+    /// If this is an internal node, also removes the edge that was to the right
+    /// of that pair and returns the orphaned node that this edge owned with its
+    /// parent erased.
     pub fn pop(&mut self) -> (K, V, Option<Root<K, V>>) {
         assert!(self.len() > 0);
 
@@ -618,7 +621,7 @@ impl<'a, K, V> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
                     let edge =
                         ptr::read(internal.as_internal().edges.get_unchecked(idx + 1).as_ptr());
                     let mut new_root = Root { node: edge, height: internal.height - 1 };
-                    (*new_root.as_mut().as_leaf_mut()).parent = ptr::null();
+                    (*new_root.node_as_mut().as_leaf_mut()).parent = ptr::null();
                     Some(new_root)
                 }
             };
@@ -650,7 +653,7 @@ impl<'a, K, V> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
                     );
 
                     let mut new_root = Root { node: edge, height: internal.height - 1 };
-                    (*new_root.as_mut().as_leaf_mut()).parent = ptr::null();
+                    (*new_root.node_as_mut().as_leaf_mut()).parent = ptr::null();
 
                     for i in 0..old_len {
                         Handle::new_edge(internal.reborrow_mut(), i).correct_parent_link();
@@ -721,7 +724,7 @@ impl<Node: Copy, Type> Clone for Handle<Node, Type> {
 }
 
 impl<Node, Type> Handle<Node, Type> {
-    /// Retrieves the node that contains the edge of key/value pair this handle points to.
+    /// Retrieves the node that contains the edge or key/value pair this handle points to.
     pub fn into_node(self) -> Node {
         self.node
     }
@@ -821,13 +824,34 @@ impl<BorrowType, K, V, NodeType> Handle<NodeRef<BorrowType, K, V, NodeType>, mar
     }
 }
 
-impl<'a, K, V> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::Edge> {
+enum InsertionPlace {
+    Left(usize),
+    Right(usize),
+}
+
+/// Given an edge index where we want to insert into a node filled to capacity,
+/// computes a sensible KV index of a split point and where to perform the insertion.
+/// The goal of the split point is for its key and value to end up in a parent node;
+/// the keys, values and edges to the left of the split point become the left child;
+/// the keys, values and edges to the right of the split point become the right child.
+fn splitpoint(edge_idx: usize) -> (usize, InsertionPlace) {
+    debug_assert!(edge_idx <= CAPACITY);
+    // Rust issue #74834 tries to explain these symmetric rules.
+    match edge_idx {
+        0..EDGE_IDX_LEFT_OF_CENTER => (KV_IDX_CENTER - 1, InsertionPlace::Left(edge_idx)),
+        EDGE_IDX_LEFT_OF_CENTER => (KV_IDX_CENTER, InsertionPlace::Left(edge_idx)),
+        EDGE_IDX_RIGHT_OF_CENTER => (KV_IDX_CENTER, InsertionPlace::Right(0)),
+        _ => (KV_IDX_CENTER + 1, InsertionPlace::Right(edge_idx - (KV_IDX_CENTER + 1 + 1))),
+    }
+}
+
+impl<'a, K, V, NodeType> Handle<NodeRef<marker::Mut<'a>, K, V, NodeType>, marker::Edge> {
+    /// Helps implementations of `insert_fit` for a particular `NodeType`,
+    /// by taking care of leaf data.
     /// Inserts a new key/value pair between the key/value pairs to the right and left of
     /// this edge. This method assumes that there is enough space in the node for the new
     /// pair to fit.
-    ///
+    fn leafy_insert_fit(&mut self, key: K, val: V) {
-    /// The returned pointer points to the inserted value.
-    fn insert_fit(&mut self, key: K, val: V) -> *mut V {
         // Necessary for correctness, but in a private module
         debug_assert!(self.node.len() < CAPACITY);
 
@@ -836,35 +860,49 @@ impl<'a, K, V> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::Edge
             slice_insert(self.node.vals_mut(), self.idx, val);
 
             (*self.node.as_leaf_mut()).len += 1;
-
-            self.node.vals_mut().get_unchecked_mut(self.idx)
         }
     }
+}
 
+impl<'a, K, V> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::Edge> {
+    /// Inserts a new key/value pair between the key/value pairs to the right and left of
+    /// this edge. This method assumes that there is enough space in the node for the new
+    /// pair to fit.
+    ///
+    /// The returned pointer points to the inserted value.
+    fn insert_fit(&mut self, key: K, val: V) -> *mut V {
+        self.leafy_insert_fit(key, val);
+        unsafe { self.node.vals_mut().get_unchecked_mut(self.idx) }
+    }
+}
+
+impl<'a, K, V> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::Edge> {
     /// Inserts a new key/value pair between the key/value pairs to the right and left of
     /// this edge. This method splits the node if there isn't enough room.
     ///
     /// The returned pointer points to the inserted value.
-    pub fn insert(mut self, key: K, val: V) -> (InsertResult<'a, K, V, marker::Leaf>, *mut V) {
+    fn insert(mut self, key: K, val: V) -> (InsertResult<'a, K, V, marker::Leaf>, *mut V) {
         if self.node.len() < CAPACITY {
             let ptr = self.insert_fit(key, val);
             let kv = unsafe { Handle::new_kv(self.node, self.idx) };
             (InsertResult::Fit(kv), ptr)
         } else {
-            let middle = unsafe { Handle::new_kv(self.node, B) };
+            let (middle_kv_idx, insertion) = splitpoint(self.idx);
+            let middle = unsafe { Handle::new_kv(self.node, middle_kv_idx) };
             let (mut left, k, v, mut right) = middle.split();
-            let ptr = if self.idx <= B {
+            let ptr = match insertion {
-                unsafe { Handle::new_edge(left.reborrow_mut(), self.idx).insert_fit(key, val) }
+                InsertionPlace::Left(insert_idx) => unsafe {
-            } else {
+                    Handle::new_edge(left.reborrow_mut(), insert_idx).insert_fit(key, val)
-                unsafe {
+                },
+                InsertionPlace::Right(insert_idx) => unsafe {
                     Handle::new_edge(
-                        right.as_mut().cast_unchecked::<marker::Leaf>(),
+                        right.node_as_mut().cast_unchecked::<marker::Leaf>(),
-                        self.idx - (B + 1),
+                        insert_idx,
                     )
                     .insert_fit(key, val)
-                }
+                },
             };
-            (InsertResult::Split(left, k, v, right), ptr)
+            (InsertResult::Split(SplitResult { left: left.forget_type(), k, v, right }), ptr)
         }
     }
 }
@@ -882,14 +920,6 @@ impl<'a, K, V> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>, marker::
         }
     }
 
-    /// Unsafely asserts to the compiler some static information about whether the underlying
-    /// node of this handle is a `Leaf`.
-    unsafe fn cast_unchecked<NewType>(
-        &mut self,
-    ) -> Handle<NodeRef<marker::Mut<'_>, K, V, NewType>, marker::Edge> {
-        unsafe { Handle::new_edge(self.node.cast_unchecked(), self.idx) }
-    }
-
     /// Inserts a new key/value pair and an edge that will go to the right of that new pair
     /// between this edge and the key/value pair to the right of this edge. This method assumes
     /// that there is enough space in the node for the new pair to fit.
@@ -899,8 +929,7 @@ impl<'a, K, V> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>, marker::
         debug_assert!(edge.height == self.node.height - 1);
 
         unsafe {
-            // This cast is a lie, but it allows us to reuse the key/value insertion logic.
+            self.leafy_insert_fit(key, val);
-            self.cast_unchecked::<marker::Leaf>().insert_fit(key, val);
 
             slice_insert(
                 slice::from_raw_parts_mut(
@@ -920,7 +949,7 @@ impl<'a, K, V> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>, marker::
     /// Inserts a new key/value pair and an edge that will go to the right of that new pair
     /// between this edge and the key/value pair to the right of this edge. This method splits
     /// the node if there isn't enough room.
-    pub fn insert(
+    fn insert(
         mut self,
         key: K,
         val: V,
@@ -933,22 +962,58 @@ impl<'a, K, V> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>, marker::
             let kv = unsafe { Handle::new_kv(self.node, self.idx) };
             InsertResult::Fit(kv)
         } else {
-            let middle = unsafe { Handle::new_kv(self.node, B) };
+            let (middle_kv_idx, insertion) = splitpoint(self.idx);
+            let middle = unsafe { Handle::new_kv(self.node, middle_kv_idx) };
             let (mut left, k, v, mut right) = middle.split();
-            if self.idx <= B {
+            match insertion {
-                unsafe {
+                InsertionPlace::Left(insert_idx) => unsafe {
-                    Handle::new_edge(left.reborrow_mut(), self.idx).insert_fit(key, val, edge);
+                    Handle::new_edge(left.reborrow_mut(), insert_idx).insert_fit(key, val, edge);
-                }
+                },
-            } else {
+                InsertionPlace::Right(insert_idx) => unsafe {
-                unsafe {
                     Handle::new_edge(
-                        right.as_mut().cast_unchecked::<marker::Internal>(),
+                        right.node_as_mut().cast_unchecked::<marker::Internal>(),
-                        self.idx - (B + 1),
+                        insert_idx,
                     )
                     .insert_fit(key, val, edge);
+                },
+            }
+            InsertResult::Split(SplitResult { left: left.forget_type(), k, v, right })
         }
     }
-            InsertResult::Split(left, k, v, right)
+}
+
+impl<'a, K: 'a, V> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::Edge> {
+    /// Inserts a new key/value pair between the key/value pairs to the right and left of
+    /// this edge. This method splits the node if there isn't enough room, and tries to
+    /// insert the split off portion into the parent node recursively, until the root is reached.
+    ///
+    /// If the returned result is a `Fit`, its handle's node can be this edge's node or an ancestor.
+    /// If the returned result is a `Split`, the `left` field will be the root node.
+    /// The returned pointer points to the inserted value.
+    pub fn insert_recursing(
+        self,
+        key: K,
+        value: V,
+    ) -> (InsertResult<'a, K, V, marker::LeafOrInternal>, *mut V) {
+        let (mut split, val_ptr) = match self.insert(key, value) {
+            (InsertResult::Fit(handle), ptr) => {
+                return (InsertResult::Fit(handle.forget_node_type()), ptr);
+            }
+            (InsertResult::Split(split), val_ptr) => (split, val_ptr),
+        };
+
+        loop {
+            split = match split.left.ascend() {
+                Ok(parent) => match parent.insert(split.k, split.v, split.right) {
+                    InsertResult::Fit(handle) => {
+                        return (InsertResult::Fit(handle.forget_node_type()), val_ptr);
+                    }
+                    InsertResult::Split(split) => split,
+                },
+                Err(root) => {
+                    return (InsertResult::Split(SplitResult { left: root, ..split }), val_ptr);
+                }
+            };
         }
     }
 }
@@ -972,14 +1037,23 @@ impl<BorrowType, K, V> Handle<NodeRef<BorrowType, K, V, marker::Internal>, marke
 
 impl<'a, K: 'a, V: 'a, NodeType> Handle<NodeRef<marker::Immut<'a>, K, V, NodeType>, marker::KV> {
     pub fn into_kv(self) -> (&'a K, &'a V) {
-        unsafe {
+        let keys = self.node.into_key_slice();
-            let (keys, vals) = self.node.into_slices();
+        let vals = self.node.into_val_slice();
-            (keys.get_unchecked(self.idx), vals.get_unchecked(self.idx))
+        unsafe { (keys.get_unchecked(self.idx), vals.get_unchecked(self.idx)) }
-        }
     }
 }
 
 impl<'a, K: 'a, V: 'a, NodeType> Handle<NodeRef<marker::Mut<'a>, K, V, NodeType>, marker::KV> {
+    pub fn into_key_mut(self) -> &'a mut K {
+        let keys = self.node.into_key_slice_mut();
+        unsafe { keys.get_unchecked_mut(self.idx) }
+    }
+
+    pub fn into_val_mut(self) -> &'a mut V {
+        let vals = self.node.into_val_slice_mut();
+        unsafe { vals.get_unchecked_mut(self.idx) }
+    }
+
     pub fn into_kv_mut(self) -> (&'a mut K, &'a mut V) {
         unsafe {
             let (keys, vals) = self.node.into_slices_mut();
@@ -997,18 +1071,11 @@ impl<'a, K, V, NodeType> Handle<NodeRef<marker::Mut<'a>, K, V, NodeType>, marker
     }
 }
 
-impl<'a, K, V> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::KV> {
+impl<'a, K, V, NodeType> Handle<NodeRef<marker::Mut<'a>, K, V, NodeType>, marker::KV> {
-    /// Splits the underlying node into three parts:
+    /// Helps implementations of `split` for a particular `NodeType`,
-    ///
+    /// by taking care of leaf data.
-    /// - The node is truncated to only contain the key/value pairs to the right of
+    fn leafy_split(&mut self, new_node: &mut LeafNode<K, V>) -> (K, V, usize) {
-    ///   this handle.
-    /// - The key and value pointed to by this handle and extracted.
-    /// - All the key/value pairs to the right of this handle are put into a newly
-    ///   allocated node.
-    pub fn split(mut self) -> (NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, K, V, Root<K, V>) {
         unsafe {
-            let mut new_node = Box::new(LeafNode::new());
-
             let k = ptr::read(self.node.keys().get_unchecked(self.idx));
             let v = ptr::read(self.node.vals().get_unchecked(self.idx));
 
@@ -1027,21 +1094,39 @@ impl<'a, K, V> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::KV>
 
             (*self.node.as_leaf_mut()).len = self.idx as u16;
             new_node.len = new_len as u16;
+            (k, v, new_len)
+        }
+    }
+}
+
+impl<'a, K, V> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::KV> {
+    /// Splits the underlying node into three parts:
+    ///
+    /// - The node is truncated to only contain the key/value pairs to the right of
+    ///   this handle.
+    /// - The key and value pointed to by this handle and extracted.
+    /// - All the key/value pairs to the right of this handle are put into a newly
+    ///   allocated node.
+    pub fn split(mut self) -> (NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, K, V, Root<K, V>) {
+        unsafe {
+            let mut new_node = Box::new(LeafNode::new());
+
+            let (k, v, _) = self.leafy_split(&mut new_node);
 
             (self.node, k, v, Root { node: BoxedNode::from_leaf(new_node), height: 0 })
         }
     }
 
     /// Removes the key/value pair pointed to by this handle and returns it, along with the edge
-    /// between the now adjacent key/value pairs (if any) to the left and right of this handle.
+    /// that the key/value pair collapsed into.
     pub fn remove(
         mut self,
-    ) -> (Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::Edge>, K, V) {
+    ) -> ((K, V), Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::Edge>) {
         unsafe {
             let k = slice_remove(self.node.keys_mut(), self.idx);
             let v = slice_remove(self.node.vals_mut(), self.idx);
             (*self.node.as_leaf_mut()).len -= 1;
-            (self.left_edge(), k, v)
+            ((k, v), self.left_edge())
         }
     }
 }
@@ -1058,35 +1143,19 @@ impl<'a, K, V> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>, marker::
         unsafe {
             let mut new_node = Box::new(InternalNode::new());
 
-            let k = ptr::read(self.node.keys().get_unchecked(self.idx));
+            let (k, v, new_len) = self.leafy_split(&mut new_node.data);
-            let v = ptr::read(self.node.vals().get_unchecked(self.idx));
-
             let height = self.node.height;
-            let new_len = self.node.len() - self.idx - 1;
 
-            ptr::copy_nonoverlapping(
-                self.node.keys().as_ptr().add(self.idx + 1),
-                new_node.data.keys.as_mut_ptr() as *mut K,
-                new_len,
-            );
-            ptr::copy_nonoverlapping(
-                self.node.vals().as_ptr().add(self.idx + 1),
-                new_node.data.vals.as_mut_ptr() as *mut V,
-                new_len,
-            );
             ptr::copy_nonoverlapping(
                 self.node.as_internal().edges.as_ptr().add(self.idx + 1),
                 new_node.edges.as_mut_ptr(),
                 new_len + 1,
             );
 
-            (*self.node.as_leaf_mut()).len = self.idx as u16;
-            new_node.data.len = new_len as u16;
-
             let mut new_root = Root { node: BoxedNode::from_internal(new_node), height };
 
             for i in 0..(new_len + 1) {
-                Handle::new_edge(new_root.as_mut().cast_unchecked(), i).correct_parent_link();
+                Handle::new_edge(new_root.node_as_mut().cast_unchecked(), i).correct_parent_link();
             }
 
             (self.node, k, v, new_root)
@@ -1107,7 +1176,7 @@ impl<'a, K, V> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>, marker::
     /// to by this handle, and the node immediately to the right of this handle into one new
     /// child of the underlying node, returning an edge referencing that new child.
     ///
-    /// Assumes that this edge `.can_merge()`.
+    /// Panics unless this edge `.can_merge()`.
     pub fn merge(
         mut self,
     ) -> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>, marker::Edge> {
@@ -1115,10 +1184,9 @@ impl<'a, K, V> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>, marker::
         let self2 = unsafe { ptr::read(&self) };
         let mut left_node = self1.left_edge().descend();
         let left_len = left_node.len();
-        let mut right_node = self2.right_edge().descend();
+        let right_node = self2.right_edge().descend();
         let right_len = right_node.len();
 
-        // necessary for correctness, but in a private module
         assert!(left_len + right_len < CAPACITY);
 
         unsafe {
@@ -1149,28 +1217,25 @@ impl<'a, K, V> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>, marker::
 
             (*left_node.as_leaf_mut()).len += right_len as u16 + 1;
 
-            let layout = if self.node.height > 1 {
+            if self.node.height > 1 {
+                // SAFETY: the height of the nodes being merged is one below the height
+                // of the node of this edge, thus above zero, so they are internal.
+                let mut left_node = left_node.cast_unchecked();
+                let right_node = right_node.cast_unchecked();
                 ptr::copy_nonoverlapping(
-                    right_node.cast_unchecked().as_internal().edges.as_ptr(),
+                    right_node.reborrow().as_internal().edges.as_ptr(),
-                    left_node
+                    left_node.reborrow_mut().as_internal_mut().edges.as_mut_ptr().add(left_len + 1),
-                        .cast_unchecked()
-                        .as_internal_mut()
-                        .edges
-                        .as_mut_ptr()
-                        .add(left_len + 1),
                     right_len + 1,
                 );
 
                 for i in left_len + 1..left_len + right_len + 2 {
-                    Handle::new_edge(left_node.cast_unchecked().reborrow_mut(), i)
+                    Handle::new_edge(left_node.reborrow_mut(), i).correct_parent_link();
-                        .correct_parent_link();
                 }
 
-                Layout::new::<InternalNode<K, V>>()
+                Global.dealloc(right_node.node.cast(), Layout::new::<InternalNode<K, V>>());
             } else {
-                Layout::new::<LeafNode<K, V>>()
+                Global.dealloc(right_node.node.cast(), Layout::new::<LeafNode<K, V>>());
-            };
+            }
-            Global.dealloc(right_node.node.cast(), layout);
 
             Handle::new_edge(self.node, self.idx)
         }
@@ -1183,8 +1248,8 @@ impl<'a, K, V> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>, marker::
         unsafe {
             let (k, v, edge) = self.reborrow_mut().left_edge().descend().pop();
 
-            let k = mem::replace(self.reborrow_mut().into_kv_mut().0, k);
+            let k = mem::replace(self.kv_mut().0, k);
-            let v = mem::replace(self.reborrow_mut().into_kv_mut().1, v);
+            let v = mem::replace(self.kv_mut().1, v);
 
             match self.reborrow_mut().right_edge().descend().force() {
                 ForceResult::Leaf(mut leaf) => leaf.push_front(k, v),
@@ -1200,8 +1265,8 @@ impl<'a, K, V> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>, marker::
         unsafe {
             let (k, v, edge) = self.reborrow_mut().right_edge().descend().pop_front();
 
-            let k = mem::replace(self.reborrow_mut().into_kv_mut().0, k);
+            let k = mem::replace(self.kv_mut().0, k);
-            let v = mem::replace(self.reborrow_mut().into_kv_mut().1, v);
+            let v = mem::replace(self.kv_mut().1, v);
 
             match self.reborrow_mut().left_edge().descend().force() {
                 ForceResult::Leaf(mut leaf) => leaf.push(k, v),
@@ -1229,7 +1294,7 @@ impl<'a, K, V> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>, marker::
                 let left_kv = left_node.reborrow_mut().into_kv_pointers_mut();
                 let right_kv = right_node.reborrow_mut().into_kv_pointers_mut();
                 let parent_kv = {
-                    let kv = self.reborrow_mut().into_kv_mut();
+                    let kv = self.kv_mut();
                     (kv.0 as *mut K, kv.1 as *mut V)
                 };
 
@@ -1286,7 +1351,7 @@ impl<'a, K, V> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>, marker::
                 let left_kv = left_node.reborrow_mut().into_kv_pointers_mut();
                 let right_kv = right_node.reborrow_mut().into_kv_pointers_mut();
                 let parent_kv = {
-                    let kv = self.reborrow_mut().into_kv_mut();
+                    let kv = self.kv_mut();
                     (kv.0 as *mut K, kv.1 as *mut V)
                 };
 
@@ -1354,6 +1419,20 @@ unsafe fn move_edges<K, V>(
     }
 }
 
+impl<BorrowType, K, V> NodeRef<BorrowType, K, V, marker::Leaf> {
+    /// Removes any static information asserting that this node is a `Leaf` node.
+    pub fn forget_type(self) -> NodeRef<BorrowType, K, V, marker::LeafOrInternal> {
+        NodeRef { height: self.height, node: self.node, root: self.root, _marker: PhantomData }
+    }
+}
+
+impl<BorrowType, K, V> NodeRef<BorrowType, K, V, marker::Internal> {
+    /// Removes any static information asserting that this node is an `Internal` node.
+    pub fn forget_type(self) -> NodeRef<BorrowType, K, V, marker::LeafOrInternal> {
+        NodeRef { height: self.height, node: self.node, root: self.root, _marker: PhantomData }
+    }
+}
+
 impl<BorrowType, K, V> Handle<NodeRef<BorrowType, K, V, marker::Leaf>, marker::Edge> {
     pub fn forget_node_type(
         self,
@@ -1378,6 +1457,14 @@ impl<BorrowType, K, V> Handle<NodeRef<BorrowType, K, V, marker::Leaf>, marker::K
     }
 }
 
+impl<BorrowType, K, V> Handle<NodeRef<BorrowType, K, V, marker::Internal>, marker::KV> {
+    pub fn forget_node_type(
+        self,
+    ) -> Handle<NodeRef<BorrowType, K, V, marker::LeafOrInternal>, marker::KV> {
+        unsafe { Handle::new_kv(self.node.forget_type(), self.idx) }
+    }
+}
+
 impl<BorrowType, K, V, HandleType>
     Handle<NodeRef<BorrowType, K, V, marker::LeafOrInternal>, HandleType>
 {
@@ -1444,9 +1531,21 @@ pub enum ForceResult<Leaf, Internal> {
     Internal(Internal),
 }
 
+/// Result of insertion, when a node needed to expand beyond its capacity.
+/// Does not distinguish between `Leaf` and `Internal` because `Root` doesn't.
+pub struct SplitResult<'a, K, V> {
+    // Altered node in existing tree with elements and edges that belong to the left of `k`.
+    pub left: NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal>,
+    // Some key and value split off, to be inserted elsewhere.
+    pub k: K,
+    pub v: V,
+    // Owned, unattached, new node with elements and edges that belong to the right of `k`.
+    pub right: Root<K, V>,
+}
+
 pub enum InsertResult<'a, K, V, Type> {
     Fit(Handle<NodeRef<marker::Mut<'a>, K, V, Type>, marker::KV>),
-    Split(NodeRef<marker::Mut<'a>, K, V, Type>, K, V, Root<K, V>),
+    Split(SplitResult<'a, K, V>),
 }
 
 pub mod marker {
@@ -1478,3 +1577,6 @@ unsafe fn slice_remove<T>(slice: &mut [T], idx: usize) -> T {
         ret
     }
 }
+
+#[cfg(test)]
+mod tests;

library/alloc/src/collections/btree/node/tests.rs

@@ -0,0 +1,25 @@
+use super::*;
+
+#[test]
+fn test_splitpoint() {
+    for idx in 0..=CAPACITY {
+        let (middle_kv_idx, insertion) = splitpoint(idx);
+
+        // Simulate performing the split:
+        let mut left_len = middle_kv_idx;
+        let mut right_len = CAPACITY - middle_kv_idx - 1;
+        match insertion {
+            InsertionPlace::Left(edge_idx) => {
+                assert!(edge_idx <= left_len);
+                left_len += 1;
+            }
+            InsertionPlace::Right(edge_idx) => {
+                assert!(edge_idx <= right_len);
+                right_len += 1;
+            }
+        }
+        assert!(left_len >= MIN_LEN);
+        assert!(right_len >= MIN_LEN);
+        assert!(left_len + right_len == CAPACITY);
+    }
+}

library/alloc/src/collections/btree/set/tests.rs

@@ -0,0 +1,649 @@
+use crate::collections::BTreeSet;
+use crate::vec::Vec;
+use std::iter::FromIterator;
+use std::panic::{catch_unwind, AssertUnwindSafe};
+use std::sync::atomic::{AtomicU32, Ordering};
+
+use super::super::DeterministicRng;
+
+#[test]
+fn test_clone_eq() {
+    let mut m = BTreeSet::new();
+
+    m.insert(1);
+    m.insert(2);
+
+    assert_eq!(m.clone(), m);
+}
+
+#[test]
+fn test_iter_min_max() {
+    let mut a = BTreeSet::new();
+    assert_eq!(a.iter().min(), None);
+    assert_eq!(a.iter().max(), None);
+    assert_eq!(a.range(..).min(), None);
+    assert_eq!(a.range(..).max(), None);
+    assert_eq!(a.difference(&BTreeSet::new()).min(), None);
+    assert_eq!(a.difference(&BTreeSet::new()).max(), None);
+    assert_eq!(a.intersection(&a).min(), None);
+    assert_eq!(a.intersection(&a).max(), None);
+    assert_eq!(a.symmetric_difference(&BTreeSet::new()).min(), None);
+    assert_eq!(a.symmetric_difference(&BTreeSet::new()).max(), None);
+    assert_eq!(a.union(&a).min(), None);
+    assert_eq!(a.union(&a).max(), None);
+    a.insert(1);
+    a.insert(2);
+    assert_eq!(a.iter().min(), Some(&1));
+    assert_eq!(a.iter().max(), Some(&2));
+    assert_eq!(a.range(..).min(), Some(&1));
+    assert_eq!(a.range(..).max(), Some(&2));
+    assert_eq!(a.difference(&BTreeSet::new()).min(), Some(&1));
+    assert_eq!(a.difference(&BTreeSet::new()).max(), Some(&2));
+    assert_eq!(a.intersection(&a).min(), Some(&1));
+    assert_eq!(a.intersection(&a).max(), Some(&2));
+    assert_eq!(a.symmetric_difference(&BTreeSet::new()).min(), Some(&1));
+    assert_eq!(a.symmetric_difference(&BTreeSet::new()).max(), Some(&2));
+    assert_eq!(a.union(&a).min(), Some(&1));
+    assert_eq!(a.union(&a).max(), Some(&2));
+}
+
+fn check<F>(a: &[i32], b: &[i32], expected: &[i32], f: F)
+where
+    F: FnOnce(&BTreeSet<i32>, &BTreeSet<i32>, &mut dyn FnMut(&i32) -> bool) -> bool,
+{
+    let mut set_a = BTreeSet::new();
+    let mut set_b = BTreeSet::new();
+
+    for x in a {
+        assert!(set_a.insert(*x))
+    }
+    for y in b {
+        assert!(set_b.insert(*y))
+    }
+
+    let mut i = 0;
+    f(&set_a, &set_b, &mut |&x| {
+        if i < expected.len() {
+            assert_eq!(x, expected[i]);
+        }
+        i += 1;
+        true
+    });
+    assert_eq!(i, expected.len());
+}
+
+#[test]
+fn test_intersection() {
+    fn check_intersection(a: &[i32], b: &[i32], expected: &[i32]) {
+        check(a, b, expected, |x, y, f| x.intersection(y).all(f))
+    }
+
+    check_intersection(&[], &[], &[]);
+    check_intersection(&[1, 2, 3], &[], &[]);
+    check_intersection(&[], &[1, 2, 3], &[]);
+    check_intersection(&[2], &[1, 2, 3], &[2]);
+    check_intersection(&[1, 2, 3], &[2], &[2]);
+    check_intersection(&[11, 1, 3, 77, 103, 5, -5], &[2, 11, 77, -9, -42, 5, 3], &[3, 5, 11, 77]);
+
+    if cfg!(miri) {
+        // Miri is too slow
+        return;
+    }
+
+    let large = (0..100).collect::<Vec<_>>();
+    check_intersection(&[], &large, &[]);
+    check_intersection(&large, &[], &[]);
+    check_intersection(&[-1], &large, &[]);
+    check_intersection(&large, &[-1], &[]);
+    check_intersection(&[0], &large, &[0]);
+    check_intersection(&large, &[0], &[0]);
+    check_intersection(&[99], &large, &[99]);
+    check_intersection(&large, &[99], &[99]);
+    check_intersection(&[100], &large, &[]);
+    check_intersection(&large, &[100], &[]);
+    check_intersection(&[11, 5000, 1, 3, 77, 8924], &large, &[1, 3, 11, 77]);
+}
+
+#[test]
+fn test_intersection_size_hint() {
+    let x: BTreeSet<i32> = [3, 4].iter().copied().collect();
+    let y: BTreeSet<i32> = [1, 2, 3].iter().copied().collect();
+    let mut iter = x.intersection(&y);
+    assert_eq!(iter.size_hint(), (1, Some(1)));
+    assert_eq!(iter.next(), Some(&3));
+    assert_eq!(iter.size_hint(), (0, Some(0)));
+    assert_eq!(iter.next(), None);
+
+    iter = y.intersection(&y);
+    assert_eq!(iter.size_hint(), (0, Some(3)));
+    assert_eq!(iter.next(), Some(&1));
+    assert_eq!(iter.size_hint(), (0, Some(2)));
+}
+
+#[test]
+fn test_difference() {
+    fn check_difference(a: &[i32], b: &[i32], expected: &[i32]) {
+        check(a, b, expected, |x, y, f| x.difference(y).all(f))
+    }
+
+    check_difference(&[], &[], &[]);
+    check_difference(&[1, 12], &[], &[1, 12]);
+    check_difference(&[], &[1, 2, 3, 9], &[]);
+    check_difference(&[1, 3, 5, 9, 11], &[3, 9], &[1, 5, 11]);
+    check_difference(&[1, 3, 5, 9, 11], &[3, 6, 9], &[1, 5, 11]);
+    check_difference(&[1, 3, 5, 9, 11], &[0, 1], &[3, 5, 9, 11]);
+    check_difference(&[1, 3, 5, 9, 11], &[11, 12], &[1, 3, 5, 9]);
+    check_difference(
+        &[-5, 11, 22, 33, 40, 42],
+        &[-12, -5, 14, 23, 34, 38, 39, 50],
+        &[11, 22, 33, 40, 42],
+    );
+
+    if cfg!(miri) {
+        // Miri is too slow
+        return;
+    }
+
+    let large = (0..100).collect::<Vec<_>>();
+    check_difference(&[], &large, &[]);
+    check_difference(&[-1], &large, &[-1]);
+    check_difference(&[0], &large, &[]);
+    check_difference(&[99], &large, &[]);
+    check_difference(&[100], &large, &[100]);
+    check_difference(&[11, 5000, 1, 3, 77, 8924], &large, &[5000, 8924]);
+    check_difference(&large, &[], &large);
+    check_difference(&large, &[-1], &large);
+    check_difference(&large, &[100], &large);
+}
+
+#[test]
+fn test_difference_size_hint() {
+    let s246: BTreeSet<i32> = [2, 4, 6].iter().copied().collect();
+    let s23456: BTreeSet<i32> = (2..=6).collect();
+    let mut iter = s246.difference(&s23456);
+    assert_eq!(iter.size_hint(), (0, Some(3)));
+    assert_eq!(iter.next(), None);
+
+    let s12345: BTreeSet<i32> = (1..=5).collect();
+    iter = s246.difference(&s12345);
+    assert_eq!(iter.size_hint(), (0, Some(3)));
+    assert_eq!(iter.next(), Some(&6));
+    assert_eq!(iter.size_hint(), (0, Some(0)));
+    assert_eq!(iter.next(), None);
+
+    let s34567: BTreeSet<i32> = (3..=7).collect();
+    iter = s246.difference(&s34567);
+    assert_eq!(iter.size_hint(), (0, Some(3)));
+    assert_eq!(iter.next(), Some(&2));
+    assert_eq!(iter.size_hint(), (0, Some(2)));
+    assert_eq!(iter.next(), None);
+
+    let s1: BTreeSet<i32> = (-9..=1).collect();
+    iter = s246.difference(&s1);
+    assert_eq!(iter.size_hint(), (3, Some(3)));
+
+    let s2: BTreeSet<i32> = (-9..=2).collect();
+    iter = s246.difference(&s2);
+    assert_eq!(iter.size_hint(), (2, Some(2)));
+    assert_eq!(iter.next(), Some(&4));
+    assert_eq!(iter.size_hint(), (1, Some(1)));
+
+    let s23: BTreeSet<i32> = (2..=3).collect();
+    iter = s246.difference(&s23);
+    assert_eq!(iter.size_hint(), (1, Some(3)));
+    assert_eq!(iter.next(), Some(&4));
+    assert_eq!(iter.size_hint(), (1, Some(1)));
+
+    let s4: BTreeSet<i32> = (4..=4).collect();
+    iter = s246.difference(&s4);
+    assert_eq!(iter.size_hint(), (2, Some(3)));
+    assert_eq!(iter.next(), Some(&2));
+    assert_eq!(iter.size_hint(), (1, Some(2)));
+    assert_eq!(iter.next(), Some(&6));
+    assert_eq!(iter.size_hint(), (0, Some(0)));
+    assert_eq!(iter.next(), None);
+
+    let s56: BTreeSet<i32> = (5..=6).collect();
+    iter = s246.difference(&s56);
+    assert_eq!(iter.size_hint(), (1, Some(3)));
+    assert_eq!(iter.next(), Some(&2));
+    assert_eq!(iter.size_hint(), (0, Some(2)));
+
+    let s6: BTreeSet<i32> = (6..=19).collect();
+    iter = s246.difference(&s6);
+    assert_eq!(iter.size_hint(), (2, Some(2)));
+    assert_eq!(iter.next(), Some(&2));
+    assert_eq!(iter.size_hint(), (1, Some(1)));
+
+    let s7: BTreeSet<i32> = (7..=19).collect();
+    iter = s246.difference(&s7);
+    assert_eq!(iter.size_hint(), (3, Some(3)));
+}
+
+#[test]
+fn test_symmetric_difference() {
+    fn check_symmetric_difference(a: &[i32], b: &[i32], expected: &[i32]) {
+        check(a, b, expected, |x, y, f| x.symmetric_difference(y).all(f))
+    }
+
+    check_symmetric_difference(&[], &[], &[]);
+    check_symmetric_difference(&[1, 2, 3], &[2], &[1, 3]);
+    check_symmetric_difference(&[2], &[1, 2, 3], &[1, 3]);
+    check_symmetric_difference(&[1, 3, 5, 9, 11], &[-2, 3, 9, 14, 22], &[-2, 1, 5, 11, 14, 22]);
+}
+
+#[test]
+fn test_symmetric_difference_size_hint() {
+    let x: BTreeSet<i32> = [2, 4].iter().copied().collect();
+    let y: BTreeSet<i32> = [1, 2, 3].iter().copied().collect();
+    let mut iter = x.symmetric_difference(&y);
+    assert_eq!(iter.size_hint(), (0, Some(5)));
+    assert_eq!(iter.next(), Some(&1));
+    assert_eq!(iter.size_hint(), (0, Some(4)));
+    assert_eq!(iter.next(), Some(&3));
+    assert_eq!(iter.size_hint(), (0, Some(1)));
+}
+
+#[test]
+fn test_union() {
+    fn check_union(a: &[i32], b: &[i32], expected: &[i32]) {
+        check(a, b, expected, |x, y, f| x.union(y).all(f))
+    }
+
+    check_union(&[], &[], &[]);
+    check_union(&[1, 2, 3], &[2], &[1, 2, 3]);
+    check_union(&[2], &[1, 2, 3], &[1, 2, 3]);
+    check_union(
+        &[1, 3, 5, 9, 11, 16, 19, 24],
+        &[-2, 1, 5, 9, 13, 19],
+        &[-2, 1, 3, 5, 9, 11, 13, 16, 19, 24],
+    );
+}
+
+#[test]
+fn test_union_size_hint() {
+    let x: BTreeSet<i32> = [2, 4].iter().copied().collect();
+    let y: BTreeSet<i32> = [1, 2, 3].iter().copied().collect();
+    let mut iter = x.union(&y);
+    assert_eq!(iter.size_hint(), (3, Some(5)));
+    assert_eq!(iter.next(), Some(&1));
+    assert_eq!(iter.size_hint(), (2, Some(4)));
+    assert_eq!(iter.next(), Some(&2));
+    assert_eq!(iter.size_hint(), (1, Some(2)));
+}
+
+#[test]
+// Only tests the simple function definition with respect to intersection
+fn test_is_disjoint() {
+    let one = [1].iter().collect::<BTreeSet<_>>();
+    let two = [2].iter().collect::<BTreeSet<_>>();
+    assert!(one.is_disjoint(&two));
+}
+
+#[test]
+// Also implicitly tests the trivial function definition of is_superset
+fn test_is_subset() {
+    fn is_subset(a: &[i32], b: &[i32]) -> bool {
+        let set_a = a.iter().collect::<BTreeSet<_>>();
+        let set_b = b.iter().collect::<BTreeSet<_>>();
+        set_a.is_subset(&set_b)
+    }
+
+    assert_eq!(is_subset(&[], &[]), true);
+    assert_eq!(is_subset(&[], &[1, 2]), true);
+    assert_eq!(is_subset(&[0], &[1, 2]), false);
+    assert_eq!(is_subset(&[1], &[1, 2]), true);
+    assert_eq!(is_subset(&[2], &[1, 2]), true);
+    assert_eq!(is_subset(&[3], &[1, 2]), false);
+    assert_eq!(is_subset(&[1, 2], &[1]), false);
+    assert_eq!(is_subset(&[1, 2], &[1, 2]), true);
+    assert_eq!(is_subset(&[1, 2], &[2, 3]), false);
+    assert_eq!(
+        is_subset(&[-5, 11, 22, 33, 40, 42], &[-12, -5, 11, 14, 22, 23, 33, 34, 38, 39, 40, 42]),
+        true
+    );
+    assert_eq!(is_subset(&[-5, 11, 22, 33, 40, 42], &[-12, -5, 11, 14, 22, 23, 34, 38]), false);
+
+    if cfg!(miri) {
+        // Miri is too slow
+        return;
+    }
+
+    let large = (0..100).collect::<Vec<_>>();
+    assert_eq!(is_subset(&[], &large), true);
+    assert_eq!(is_subset(&large, &[]), false);
+    assert_eq!(is_subset(&[-1], &large), false);
+    assert_eq!(is_subset(&[0], &large), true);
+    assert_eq!(is_subset(&[1, 2], &large), true);
+    assert_eq!(is_subset(&[99, 100], &large), false);
+}
+
+#[test]
+fn test_drain_filter() {
+    let mut x: BTreeSet<_> = [1].iter().copied().collect();
+    let mut y: BTreeSet<_> = [1].iter().copied().collect();
+
+    x.drain_filter(|_| true);
+    y.drain_filter(|_| false);
+    assert_eq!(x.len(), 0);
+    assert_eq!(y.len(), 1);
+}
+
+#[test]
+fn test_drain_filter_drop_panic_leak() {
+    static PREDS: AtomicU32 = AtomicU32::new(0);
+    static DROPS: AtomicU32 = AtomicU32::new(0);
+
+    #[derive(PartialEq, Eq, PartialOrd, Ord)]
+    struct D(i32);
+    impl Drop for D {
+        fn drop(&mut self) {
+            if DROPS.fetch_add(1, Ordering::SeqCst) == 1 {
+                panic!("panic in `drop`");
+            }
+        }
+    }
+
+    let mut set = BTreeSet::new();
+    set.insert(D(0));
+    set.insert(D(4));
+    set.insert(D(8));
+
+    catch_unwind(move || {
+        drop(set.drain_filter(|d| {
+            PREDS.fetch_add(1u32 << d.0, Ordering::SeqCst);
+            true
+        }))
+    })
+    .ok();
+
+    assert_eq!(PREDS.load(Ordering::SeqCst), 0x011);
+    assert_eq!(DROPS.load(Ordering::SeqCst), 3);
+}
+
+#[test]
+fn test_drain_filter_pred_panic_leak() {
+    static PREDS: AtomicU32 = AtomicU32::new(0);
+    static DROPS: AtomicU32 = AtomicU32::new(0);
+
+    #[derive(PartialEq, Eq, PartialOrd, Ord)]
+    struct D(i32);
+    impl Drop for D {
+        fn drop(&mut self) {
+            DROPS.fetch_add(1, Ordering::SeqCst);
+        }
+    }
+
+    let mut set = BTreeSet::new();
+    set.insert(D(0));
+    set.insert(D(4));
+    set.insert(D(8));
+
+    catch_unwind(AssertUnwindSafe(|| {
+        drop(set.drain_filter(|d| {
+            PREDS.fetch_add(1u32 << d.0, Ordering::SeqCst);
+            match d.0 {
+                0 => true,
+                _ => panic!(),
+            }
+        }))
+    }))
+    .ok();
+
+    assert_eq!(PREDS.load(Ordering::SeqCst), 0x011);
+    assert_eq!(DROPS.load(Ordering::SeqCst), 1);
+    assert_eq!(set.len(), 2);
+    assert_eq!(set.first().unwrap().0, 4);
+    assert_eq!(set.last().unwrap().0, 8);
+}
+
+#[test]
+fn test_clear() {
+    let mut x = BTreeSet::new();
+    x.insert(1);
+
+    x.clear();
+    assert!(x.is_empty());
+}
+
+#[test]
+fn test_zip() {
+    let mut x = BTreeSet::new();
+    x.insert(5);
+    x.insert(12);
+    x.insert(11);
+
+    let mut y = BTreeSet::new();
+    y.insert("foo");
+    y.insert("bar");
+
+    let x = x;
+    let y = y;
+    let mut z = x.iter().zip(&y);
+
+    assert_eq!(z.next().unwrap(), (&5, &("bar")));
+    assert_eq!(z.next().unwrap(), (&11, &("foo")));
+    assert!(z.next().is_none());
+}
+
+#[test]
+fn test_from_iter() {
+    let xs = [1, 2, 3, 4, 5, 6, 7, 8, 9];
+
+    let set: BTreeSet<_> = xs.iter().cloned().collect();
+
+    for x in &xs {
+        assert!(set.contains(x));
+    }
+}
+
+#[test]
+fn test_show() {
+    let mut set = BTreeSet::new();
+    let empty = BTreeSet::<i32>::new();
+
+    set.insert(1);
+    set.insert(2);
+
+    let set_str = format!("{:?}", set);
+
+    assert_eq!(set_str, "{1, 2}");
+    assert_eq!(format!("{:?}", empty), "{}");
+}
+
+#[test]
+fn test_extend_ref() {
+    let mut a = BTreeSet::new();
+    a.insert(1);
+
+    a.extend(&[2, 3, 4]);
+
+    assert_eq!(a.len(), 4);
+    assert!(a.contains(&1));
+    assert!(a.contains(&2));
+    assert!(a.contains(&3));
+    assert!(a.contains(&4));
+
+    let mut b = BTreeSet::new();
+    b.insert(5);
+    b.insert(6);
+
+    a.extend(&b);
+
+    assert_eq!(a.len(), 6);
+    assert!(a.contains(&1));
+    assert!(a.contains(&2));
+    assert!(a.contains(&3));
+    assert!(a.contains(&4));
+    assert!(a.contains(&5));
+    assert!(a.contains(&6));
+}
+
+#[test]
+fn test_recovery() {
+    use std::cmp::Ordering;
+
+    #[derive(Debug)]
+    struct Foo(&'static str, i32);
+
+    impl PartialEq for Foo {
+        fn eq(&self, other: &Self) -> bool {
+            self.0 == other.0
+        }
+    }
+
+    impl Eq for Foo {}
+
+    impl PartialOrd for Foo {
+        fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+            self.0.partial_cmp(&other.0)
+        }
+    }
+
+    impl Ord for Foo {
+        fn cmp(&self, other: &Self) -> Ordering {
+            self.0.cmp(&other.0)
+        }
+    }
+
+    let mut s = BTreeSet::new();
+    assert_eq!(s.replace(Foo("a", 1)), None);
+    assert_eq!(s.len(), 1);
+    assert_eq!(s.replace(Foo("a", 2)), Some(Foo("a", 1)));
+    assert_eq!(s.len(), 1);
+
+    {
+        let mut it = s.iter();
+        assert_eq!(it.next(), Some(&Foo("a", 2)));
+        assert_eq!(it.next(), None);
+    }
+
+    assert_eq!(s.get(&Foo("a", 1)), Some(&Foo("a", 2)));
+    assert_eq!(s.take(&Foo("a", 1)), Some(Foo("a", 2)));
+    assert_eq!(s.len(), 0);
+
+    assert_eq!(s.get(&Foo("a", 1)), None);
+    assert_eq!(s.take(&Foo("a", 1)), None);
+
+    assert_eq!(s.iter().next(), None);
+}
+
+#[test]
+#[allow(dead_code)]
+fn test_variance() {
+    use std::collections::btree_set::{IntoIter, Iter, Range};
+
+    fn set<'new>(v: BTreeSet<&'static str>) -> BTreeSet<&'new str> {
+        v
+    }
+    fn iter<'a, 'new>(v: Iter<'a, &'static str>) -> Iter<'a, &'new str> {
+        v
+    }
+    fn into_iter<'new>(v: IntoIter<&'static str>) -> IntoIter<&'new str> {
+        v
+    }
+    fn range<'a, 'new>(v: Range<'a, &'static str>) -> Range<'a, &'new str> {
+        v
+    }
+}
+
+#[test]
+fn test_append() {
+    let mut a = BTreeSet::new();
+    a.insert(1);
+    a.insert(2);
+    a.insert(3);
+
+    let mut b = BTreeSet::new();
+    b.insert(3);
+    b.insert(4);
+    b.insert(5);
+
+    a.append(&mut b);
+
+    assert_eq!(a.len(), 5);
+    assert_eq!(b.len(), 0);
+
+    assert_eq!(a.contains(&1), true);
+    assert_eq!(a.contains(&2), true);
+    assert_eq!(a.contains(&3), true);
+    assert_eq!(a.contains(&4), true);
+    assert_eq!(a.contains(&5), true);
+}
+
+#[test]
+fn test_first_last() {
+    let mut a = BTreeSet::new();
+    assert_eq!(a.first(), None);
+    assert_eq!(a.last(), None);
+    a.insert(1);
+    assert_eq!(a.first(), Some(&1));
+    assert_eq!(a.last(), Some(&1));
+    a.insert(2);
+    assert_eq!(a.first(), Some(&1));
+    assert_eq!(a.last(), Some(&2));
+    for i in 3..=12 {
+        a.insert(i);
+    }
+    assert_eq!(a.first(), Some(&1));
+    assert_eq!(a.last(), Some(&12));
+    assert_eq!(a.pop_first(), Some(1));
+    assert_eq!(a.pop_last(), Some(12));
+    assert_eq!(a.pop_first(), Some(2));
+    assert_eq!(a.pop_last(), Some(11));
+    assert_eq!(a.pop_first(), Some(3));
+    assert_eq!(a.pop_last(), Some(10));
+    assert_eq!(a.pop_first(), Some(4));
+    assert_eq!(a.pop_first(), Some(5));
+    assert_eq!(a.pop_first(), Some(6));
+    assert_eq!(a.pop_first(), Some(7));
+    assert_eq!(a.pop_first(), Some(8));
+    assert_eq!(a.clone().pop_last(), Some(9));
+    assert_eq!(a.pop_first(), Some(9));
+    assert_eq!(a.pop_first(), None);
+    assert_eq!(a.pop_last(), None);
+}
+
+fn rand_data(len: usize) -> Vec<u32> {
+    let mut rng = DeterministicRng::new();
+    Vec::from_iter((0..len).map(|_| rng.next()))
+}
+
+#[test]
+fn test_split_off_empty_right() {
+    let mut data = rand_data(173);
+
+    let mut set = BTreeSet::from_iter(data.clone());
+    let right = set.split_off(&(data.iter().max().unwrap() + 1));
+
+    data.sort();
+    assert!(set.into_iter().eq(data));
+    assert!(right.into_iter().eq(None));
+}
+
+#[test]
+fn test_split_off_empty_left() {
+    let mut data = rand_data(314);
+
+    let mut set = BTreeSet::from_iter(data.clone());
+    let right = set.split_off(data.iter().min().unwrap());
+
+    data.sort();
+    assert!(set.into_iter().eq(None));
+    assert!(right.into_iter().eq(data));
+}
+
+#[test]
+fn test_split_off_large_random_sorted() {
+    // Miri is too slow
+    let mut data = if cfg!(miri) { rand_data(529) } else { rand_data(1529) };
+    // special case with maximum height.
+    data.sort();
+
+    let mut set = BTreeSet::from_iter(data.clone());
+    let key = data[data.len() / 2];
+    let right = set.split_off(&key);
+
+    assert!(set.into_iter().eq(data.clone().into_iter().filter(|x| *x < key)));
+    assert!(right.into_iter().eq(data.into_iter().filter(|x| *x >= key)));
+}

library/alloc/src/collections/linked_list.rs

@@ -7,8 +7,8 @@
 //! array-based containers are generally faster,
 //! more memory efficient, and make better use of CPU cache.
 //!
-//! [`Vec`]: ../../vec/struct.Vec.html
+//! [`Vec`]: crate::vec::Vec
-//! [`VecDeque`]: ../vec_deque/struct.VecDeque.html
+//! [`VecDeque`]: super::vec_deque::VecDeque
 
 #![stable(feature = "rust1", since = "1.0.0")]
 
@@ -50,11 +50,8 @@ struct Node<T> {
 
 /// An iterator over the elements of a `LinkedList`.
 ///
-/// This `struct` is created by the [`iter`] method on [`LinkedList`]. See its
+/// This `struct` is created by [`LinkedList::iter()`]. See its
 /// documentation for more.
-///
-/// [`iter`]: struct.LinkedList.html#method.iter
-/// [`LinkedList`]: struct.LinkedList.html
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct Iter<'a, T: 'a> {
     head: Option<NonNull<Node<T>>>,
@@ -80,11 +77,8 @@ impl<T> Clone for Iter<'_, T> {
 
 /// A mutable iterator over the elements of a `LinkedList`.
 ///
-/// This `struct` is created by the [`iter_mut`] method on [`LinkedList`]. See its
+/// This `struct` is created by [`LinkedList::iter_mut()`]. See its
 /// documentation for more.
-///
-/// [`iter_mut`]: struct.LinkedList.html#method.iter_mut
-/// [`LinkedList`]: struct.LinkedList.html
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct IterMut<'a, T: 'a> {
     // We do *not* exclusively own the entire list here, references to node's `element`
@@ -109,7 +103,6 @@ impl<T: fmt::Debug> fmt::Debug for IterMut<'_, T> {
 /// (provided by the `IntoIterator` trait). See its documentation for more.
 ///
 /// [`into_iter`]: struct.LinkedList.html#method.into_iter
-/// [`LinkedList`]: struct.LinkedList.html
 #[derive(Clone)]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct IntoIter<T> {
@@ -404,7 +397,7 @@ impl<T> LinkedList<T> {
     /// This reuses all the nodes from `other` and moves them into `self`. After
     /// this operation, `other` becomes empty.
     ///
-    /// This operation should compute in `O(1)` time and `O(1)` memory.
+    /// This operation should compute in *O*(1) time and *O*(1) memory.
     ///
     /// # Examples
     ///
@@ -561,7 +554,7 @@ impl<T> LinkedList<T> {
 
     /// Returns `true` if the `LinkedList` is empty.
     ///
-    /// This operation should compute in `O(1)` time.
+    /// This operation should compute in *O*(1) time.
     ///
     /// # Examples
     ///
@@ -582,7 +575,7 @@ impl<T> LinkedList<T> {
 
     /// Returns the length of the `LinkedList`.
     ///
-    /// This operation should compute in `O(1)` time.
+    /// This operation should compute in *O*(1) time.
     ///
     /// # Examples
     ///
@@ -608,7 +601,7 @@ impl<T> LinkedList<T> {
 
     /// Removes all elements from the `LinkedList`.
     ///
-    /// This operation should compute in `O(n)` time.
+    /// This operation should compute in *O*(*n*) time.
     ///
     /// # Examples
     ///
@@ -751,7 +744,7 @@ impl<T> LinkedList<T> {
 
     /// Adds an element first in the list.
     ///
-    /// This operation should compute in `O(1)` time.
+    /// This operation should compute in *O*(1) time.
     ///
     /// # Examples
     ///
@@ -774,7 +767,7 @@ impl<T> LinkedList<T> {
     /// Removes the first element and returns it, or `None` if the list is
     /// empty.
     ///
-    /// This operation should compute in `O(1)` time.
+    /// This operation should compute in *O*(1) time.
     ///
     /// # Examples
     ///
@@ -797,7 +790,7 @@ impl<T> LinkedList<T> {
 
     /// Appends an element to the back of a list.
     ///
-    /// This operation should compute in `O(1)` time.
+    /// This operation should compute in *O*(1) time.
     ///
     /// # Examples
     ///
@@ -817,7 +810,7 @@ impl<T> LinkedList<T> {
     /// Removes the last element from a list and returns it, or `None` if
     /// it is empty.
     ///
-    /// This operation should compute in `O(1)` time.
+    /// This operation should compute in *O*(1) time.
     ///
     /// # Examples
     ///
@@ -838,7 +831,7 @@ impl<T> LinkedList<T> {
     /// Splits the list into two at the given index. Returns everything after the given index,
     /// including the index.
     ///
-    /// This operation should compute in `O(n)` time.
+    /// This operation should compute in *O*(*n*) time.
     ///
     /// # Panics
     ///
@@ -894,7 +887,7 @@ impl<T> LinkedList<T> {
 
     /// Removes the element at the given index and returns it.
     ///
-    /// This operation should compute in `O(n)` time.
+    /// This operation should compute in *O*(*n*) time.
     ///
     /// # Panics
     /// Panics if at >= len
@@ -1110,32 +1103,17 @@ impl<T> IterMut<'_, T> {
     /// Inserts the given element just after the element most recently returned by `.next()`.
     /// The inserted element does not appear in the iteration.
     ///
-    /// # Examples
+    /// This method will be removed soon.
-    ///
-    /// ```
-    /// #![feature(linked_list_extras)]
-    ///
-    /// use std::collections::LinkedList;
-    ///
-    /// let mut list: LinkedList<_> = vec![1, 3, 4].into_iter().collect();
-    ///
-    /// {
-    ///     let mut it = list.iter_mut();
-    ///     assert_eq!(it.next().unwrap(), &1);
-    ///     // insert `2` after `1`
-    ///     it.insert_next(2);
-    /// }
-    /// {
-    ///     let vec: Vec<_> = list.into_iter().collect();
-    ///     assert_eq!(vec, [1, 2, 3, 4]);
-    /// }
-    /// ```
     #[inline]
     #[unstable(
         feature = "linked_list_extras",
         reason = "this is probably better handled by a cursor type -- we'll see",
         issue = "27794"
     )]
+    #[rustc_deprecated(
+        reason = "Deprecated in favor of CursorMut methods. This method will be removed soon.",
+        since = "1.47.0"
+    )]
     pub fn insert_next(&mut self, element: T) {
         match self.head {
             // `push_back` is okay with aliasing `element` references
@@ -1163,27 +1141,17 @@ impl<T> IterMut<'_, T> {
 
     /// Provides a reference to the next element, without changing the iterator.
     ///
-    /// # Examples
+    /// This method will be removed soon.
-    ///
-    /// ```
-    /// #![feature(linked_list_extras)]
-    ///
-    /// use std::collections::LinkedList;
-    ///
-    /// let mut list: LinkedList<_> = vec![1, 2, 3].into_iter().collect();
-    ///
-    /// let mut it = list.iter_mut();
-    /// assert_eq!(it.next().unwrap(), &1);
-    /// assert_eq!(it.peek_next().unwrap(), &2);
-    /// // We just peeked at 2, so it was not consumed from the iterator.
-    /// assert_eq!(it.next().unwrap(), &2);
-    /// ```
     #[inline]
     #[unstable(
         feature = "linked_list_extras",
         reason = "this is probably better handled by a cursor type -- we'll see",
         issue = "27794"
     )]
+    #[rustc_deprecated(
+        reason = "Deprecated in favor of CursorMut methods. This method will be removed soon.",
+        since = "1.47.0"
+    )]
     pub fn peek_next(&mut self) -> Option<&mut T> {
         if self.len == 0 {
             None

library/alloc/src/collections/linked_list/tests.rs

@@ -0,0 +1,430 @@
+use super::*;
+
+use std::thread;
+use std::vec::Vec;
+
+use rand::{thread_rng, RngCore};
+
+fn list_from<T: Clone>(v: &[T]) -> LinkedList<T> {
+    v.iter().cloned().collect()
+}
+
+pub fn check_links<T>(list: &LinkedList<T>) {
+    unsafe {
+        let mut len = 0;
+        let mut last_ptr: Option<&Node<T>> = None;
+        let mut node_ptr: &Node<T>;
+        match list.head {
+            None => {
+                // tail node should also be None.
+                assert!(list.tail.is_none());
+                assert_eq!(0, list.len);
+                return;
+            }
+            Some(node) => node_ptr = &*node.as_ptr(),
+        }
+        loop {
+            match (last_ptr, node_ptr.prev) {
+                (None, None) => {}
+                (None, _) => panic!("prev link for head"),
+                (Some(p), Some(pptr)) => {
+                    assert_eq!(p as *const Node<T>, pptr.as_ptr() as *const Node<T>);
+                }
+                _ => panic!("prev link is none, not good"),
+            }
+            match node_ptr.next {
+                Some(next) => {
+                    last_ptr = Some(node_ptr);
+                    node_ptr = &*next.as_ptr();
+                    len += 1;
+                }
+                None => {
+                    len += 1;
+                    break;
+                }
+            }
+        }
+
+        // verify that the tail node points to the last node.
+        let tail = list.tail.as_ref().expect("some tail node").as_ref();
+        assert_eq!(tail as *const Node<T>, node_ptr as *const Node<T>);
+        // check that len matches interior links.
+        assert_eq!(len, list.len);
+    }
+}
+
+#[test]
+fn test_append() {
+    // Empty to empty
+    {
+        let mut m = LinkedList::<i32>::new();
+        let mut n = LinkedList::new();
+        m.append(&mut n);
+        check_links(&m);
+        assert_eq!(m.len(), 0);
+        assert_eq!(n.len(), 0);
+    }
+    // Non-empty to empty
+    {
+        let mut m = LinkedList::new();
+        let mut n = LinkedList::new();
+        n.push_back(2);
+        m.append(&mut n);
+        check_links(&m);
+        assert_eq!(m.len(), 1);
+        assert_eq!(m.pop_back(), Some(2));
+        assert_eq!(n.len(), 0);
+        check_links(&m);
+    }
+    // Empty to non-empty
+    {
+        let mut m = LinkedList::new();
+        let mut n = LinkedList::new();
+        m.push_back(2);
+        m.append(&mut n);
+        check_links(&m);
+        assert_eq!(m.len(), 1);
+        assert_eq!(m.pop_back(), Some(2));
+        check_links(&m);
+    }
+
+    // Non-empty to non-empty
+    let v = vec![1, 2, 3, 4, 5];
+    let u = vec![9, 8, 1, 2, 3, 4, 5];
+    let mut m = list_from(&v);
+    let mut n = list_from(&u);
+    m.append(&mut n);
+    check_links(&m);
+    let mut sum = v;
+    sum.extend_from_slice(&u);
+    assert_eq!(sum.len(), m.len());
+    for elt in sum {
+        assert_eq!(m.pop_front(), Some(elt))
+    }
+    assert_eq!(n.len(), 0);
+    // Let's make sure it's working properly, since we
+    // did some direct changes to private members.
+    n.push_back(3);
+    assert_eq!(n.len(), 1);
+    assert_eq!(n.pop_front(), Some(3));
+    check_links(&n);
+}
+
+#[test]
+fn test_clone_from() {
+    // Short cloned from long
+    {
+        let v = vec![1, 2, 3, 4, 5];
+        let u = vec![8, 7, 6, 2, 3, 4, 5];
+        let mut m = list_from(&v);
+        let n = list_from(&u);
+        m.clone_from(&n);
+        check_links(&m);
+        assert_eq!(m, n);
+        for elt in u {
+            assert_eq!(m.pop_front(), Some(elt))
+        }
+    }
+    // Long cloned from short
+    {
+        let v = vec![1, 2, 3, 4, 5];
+        let u = vec![6, 7, 8];
+        let mut m = list_from(&v);
+        let n = list_from(&u);
+        m.clone_from(&n);
+        check_links(&m);
+        assert_eq!(m, n);
+        for elt in u {
+            assert_eq!(m.pop_front(), Some(elt))
+        }
+    }
+    // Two equal length lists
+    {
+        let v = vec![1, 2, 3, 4, 5];
+        let u = vec![9, 8, 1, 2, 3];
+        let mut m = list_from(&v);
+        let n = list_from(&u);
+        m.clone_from(&n);
+        check_links(&m);
+        assert_eq!(m, n);
+        for elt in u {
+            assert_eq!(m.pop_front(), Some(elt))
+        }
+    }
+}
+
+#[test]
+#[cfg_attr(target_os = "emscripten", ignore)]
+fn test_send() {
+    let n = list_from(&[1, 2, 3]);
+    thread::spawn(move || {
+        check_links(&n);
+        let a: &[_] = &[&1, &2, &3];
+        assert_eq!(a, &*n.iter().collect::<Vec<_>>());
+    })
+    .join()
+    .ok()
+    .unwrap();
+}
+
+#[test]
+fn test_fuzz() {
+    for _ in 0..25 {
+        fuzz_test(3);
+        fuzz_test(16);
+        #[cfg(not(miri))] // Miri is too slow
+        fuzz_test(189);
+    }
+}
+
+#[test]
+fn test_26021() {
+    // There was a bug in split_off that failed to null out the RHS's head's prev ptr.
+    // This caused the RHS's dtor to walk up into the LHS at drop and delete all of
+    // its nodes.
+    //
+    // https://github.com/rust-lang/rust/issues/26021
+    let mut v1 = LinkedList::new();
+    v1.push_front(1);
+    v1.push_front(1);
+    v1.push_front(1);
+    v1.push_front(1);
+    let _ = v1.split_off(3); // Dropping this now should not cause laundry consumption
+    assert_eq!(v1.len(), 3);
+
+    assert_eq!(v1.iter().len(), 3);
+    assert_eq!(v1.iter().collect::<Vec<_>>().len(), 3);
+}
+
+#[test]
+fn test_split_off() {
+    let mut v1 = LinkedList::new();
+    v1.push_front(1);
+    v1.push_front(1);
+    v1.push_front(1);
+    v1.push_front(1);
+
+    // test all splits
+    for ix in 0..1 + v1.len() {
+        let mut a = v1.clone();
+        let b = a.split_off(ix);
+        check_links(&a);
+        check_links(&b);
+        a.extend(b);
+        assert_eq!(v1, a);
+    }
+}
+
+fn fuzz_test(sz: i32) {
+    let mut m: LinkedList<_> = LinkedList::new();
+    let mut v = vec![];
+    for i in 0..sz {
+        check_links(&m);
+        let r: u8 = thread_rng().next_u32() as u8;
+        match r % 6 {
+            0 => {
+                m.pop_back();
+                v.pop();
+            }
+            1 => {
+                if !v.is_empty() {
+                    m.pop_front();
+                    v.remove(0);
+                }
+            }
+            2 | 4 => {
+                m.push_front(-i);
+                v.insert(0, -i);
+            }
+            3 | 5 | _ => {
+                m.push_back(i);
+                v.push(i);
+            }
+        }
+    }
+
+    check_links(&m);
+
+    let mut i = 0;
+    for (a, &b) in m.into_iter().zip(&v) {
+        i += 1;
+        assert_eq!(a, b);
+    }
+    assert_eq!(i, v.len());
+}
+
+#[test]
+fn drain_filter_test() {
+    let mut m: LinkedList<u32> = LinkedList::new();
+    m.extend(&[1, 2, 3, 4, 5, 6]);
+    let deleted = m.drain_filter(|v| *v < 4).collect::<Vec<_>>();
+
+    check_links(&m);
+
+    assert_eq!(deleted, &[1, 2, 3]);
+    assert_eq!(m.into_iter().collect::<Vec<_>>(), &[4, 5, 6]);
+}
+
+#[test]
+fn drain_to_empty_test() {
+    let mut m: LinkedList<u32> = LinkedList::new();
+    m.extend(&[1, 2, 3, 4, 5, 6]);
+    let deleted = m.drain_filter(|_| true).collect::<Vec<_>>();
+
+    check_links(&m);
+
+    assert_eq!(deleted, &[1, 2, 3, 4, 5, 6]);
+    assert_eq!(m.into_iter().collect::<Vec<_>>(), &[]);
+}
+
+#[test]
+fn test_cursor_move_peek() {
+    let mut m: LinkedList<u32> = LinkedList::new();
+    m.extend(&[1, 2, 3, 4, 5, 6]);
+    let mut cursor = m.cursor_front();
+    assert_eq!(cursor.current(), Some(&1));
+    assert_eq!(cursor.peek_next(), Some(&2));
+    assert_eq!(cursor.peek_prev(), None);
+    assert_eq!(cursor.index(), Some(0));
+    cursor.move_prev();
+    assert_eq!(cursor.current(), None);
+    assert_eq!(cursor.peek_next(), Some(&1));
+    assert_eq!(cursor.peek_prev(), Some(&6));
+    assert_eq!(cursor.index(), None);
+    cursor.move_next();
+    cursor.move_next();
+    assert_eq!(cursor.current(), Some(&2));
+    assert_eq!(cursor.peek_next(), Some(&3));
+    assert_eq!(cursor.peek_prev(), Some(&1));
+    assert_eq!(cursor.index(), Some(1));
+
+    let mut cursor = m.cursor_back();
+    assert_eq!(cursor.current(), Some(&6));
+    assert_eq!(cursor.peek_next(), None);
+    assert_eq!(cursor.peek_prev(), Some(&5));
+    assert_eq!(cursor.index(), Some(5));
+    cursor.move_next();
+    assert_eq!(cursor.current(), None);
+    assert_eq!(cursor.peek_next(), Some(&1));
+    assert_eq!(cursor.peek_prev(), Some(&6));
+    assert_eq!(cursor.index(), None);
+    cursor.move_prev();
+    cursor.move_prev();
+    assert_eq!(cursor.current(), Some(&5));
+    assert_eq!(cursor.peek_next(), Some(&6));
+    assert_eq!(cursor.peek_prev(), Some(&4));
+    assert_eq!(cursor.index(), Some(4));
+
+    let mut m: LinkedList<u32> = LinkedList::new();
+    m.extend(&[1, 2, 3, 4, 5, 6]);
+    let mut cursor = m.cursor_front_mut();
+    assert_eq!(cursor.current(), Some(&mut 1));
+    assert_eq!(cursor.peek_next(), Some(&mut 2));
+    assert_eq!(cursor.peek_prev(), None);
+    assert_eq!(cursor.index(), Some(0));
+    cursor.move_prev();
+    assert_eq!(cursor.current(), None);
+    assert_eq!(cursor.peek_next(), Some(&mut 1));
+    assert_eq!(cursor.peek_prev(), Some(&mut 6));
+    assert_eq!(cursor.index(), None);
+    cursor.move_next();
+    cursor.move_next();
+    assert_eq!(cursor.current(), Some(&mut 2));
+    assert_eq!(cursor.peek_next(), Some(&mut 3));
+    assert_eq!(cursor.peek_prev(), Some(&mut 1));
+    assert_eq!(cursor.index(), Some(1));
+    let mut cursor2 = cursor.as_cursor();
+    assert_eq!(cursor2.current(), Some(&2));
+    assert_eq!(cursor2.index(), Some(1));
+    cursor2.move_next();
+    assert_eq!(cursor2.current(), Some(&3));
+    assert_eq!(cursor2.index(), Some(2));
+    assert_eq!(cursor.current(), Some(&mut 2));
+    assert_eq!(cursor.index(), Some(1));
+
+    let mut m: LinkedList<u32> = LinkedList::new();
+    m.extend(&[1, 2, 3, 4, 5, 6]);
+    let mut cursor = m.cursor_back_mut();
+    assert_eq!(cursor.current(), Some(&mut 6));
+    assert_eq!(cursor.peek_next(), None);
+    assert_eq!(cursor.peek_prev(), Some(&mut 5));
+    assert_eq!(cursor.index(), Some(5));
+    cursor.move_next();
+    assert_eq!(cursor.current(), None);
+    assert_eq!(cursor.peek_next(), Some(&mut 1));
+    assert_eq!(cursor.peek_prev(), Some(&mut 6));
+    assert_eq!(cursor.index(), None);
+    cursor.move_prev();
+    cursor.move_prev();
+    assert_eq!(cursor.current(), Some(&mut 5));
+    assert_eq!(cursor.peek_next(), Some(&mut 6));
+    assert_eq!(cursor.peek_prev(), Some(&mut 4));
+    assert_eq!(cursor.index(), Some(4));
+    let mut cursor2 = cursor.as_cursor();
+    assert_eq!(cursor2.current(), Some(&5));
+    assert_eq!(cursor2.index(), Some(4));
+    cursor2.move_prev();
+    assert_eq!(cursor2.current(), Some(&4));
+    assert_eq!(cursor2.index(), Some(3));
+    assert_eq!(cursor.current(), Some(&mut 5));
+    assert_eq!(cursor.index(), Some(4));
+}
+
+#[test]
+fn test_cursor_mut_insert() {
+    let mut m: LinkedList<u32> = LinkedList::new();
+    m.extend(&[1, 2, 3, 4, 5, 6]);
+    let mut cursor = m.cursor_front_mut();
+    cursor.insert_before(7);
+    cursor.insert_after(8);
+    check_links(&m);
+    assert_eq!(m.iter().cloned().collect::<Vec<_>>(), &[7, 1, 8, 2, 3, 4, 5, 6]);
+    let mut cursor = m.cursor_front_mut();
+    cursor.move_prev();
+    cursor.insert_before(9);
+    cursor.insert_after(10);
+    check_links(&m);
+    assert_eq!(m.iter().cloned().collect::<Vec<_>>(), &[10, 7, 1, 8, 2, 3, 4, 5, 6, 9]);
+    let mut cursor = m.cursor_front_mut();
+    cursor.move_prev();
+    assert_eq!(cursor.remove_current(), None);
+    cursor.move_next();
+    cursor.move_next();
+    assert_eq!(cursor.remove_current(), Some(7));
+    cursor.move_prev();
+    cursor.move_prev();
+    cursor.move_prev();
+    assert_eq!(cursor.remove_current(), Some(9));
+    cursor.move_next();
+    assert_eq!(cursor.remove_current(), Some(10));
+    check_links(&m);
+    assert_eq!(m.iter().cloned().collect::<Vec<_>>(), &[1, 8, 2, 3, 4, 5, 6]);
+    let mut cursor = m.cursor_front_mut();
+    let mut p: LinkedList<u32> = LinkedList::new();
+    p.extend(&[100, 101, 102, 103]);
+    let mut q: LinkedList<u32> = LinkedList::new();
+    q.extend(&[200, 201, 202, 203]);
+    cursor.splice_after(p);
+    cursor.splice_before(q);
+    check_links(&m);
+    assert_eq!(
+        m.iter().cloned().collect::<Vec<_>>(),
+        &[200, 201, 202, 203, 1, 100, 101, 102, 103, 8, 2, 3, 4, 5, 6]
+    );
+    let mut cursor = m.cursor_front_mut();
+    cursor.move_prev();
+    let tmp = cursor.split_before();
+    assert_eq!(m.into_iter().collect::<Vec<_>>(), &[]);
+    m = tmp;
+    let mut cursor = m.cursor_front_mut();
+    cursor.move_next();
+    cursor.move_next();
+    cursor.move_next();
+    cursor.move_next();
+    cursor.move_next();
+    cursor.move_next();
+    let tmp = cursor.split_after();
+    assert_eq!(tmp.into_iter().collect::<Vec<_>>(), &[102, 103, 8, 2, 3, 4, 5, 6]);
+    check_links(&m);
+    assert_eq!(m.iter().cloned().collect::<Vec<_>>(), &[200, 201, 202, 203, 1, 100, 101]);
+}

library/alloc/src/collections/vec_deque.rs

@@ -1,7 +1,7 @@
 //! A double-ended queue implemented with a growable ring buffer.
 //!
-//! This queue has `O(1)` amortized inserts and removals from both ends of the
+//! This queue has *O*(1) amortized inserts and removals from both ends of the
-//! container. It also has `O(1)` indexing like a vector. The contained elements
+//! container. It also has *O*(1) indexing like a vector. The contained elements
 //! are not required to be copyable, and the queue will be sendable if the
 //! contained type is sendable.
 
@@ -9,7 +9,6 @@
 
 // ignore-tidy-filelength
 
-use core::array::LengthAtMost32;
 use core::cmp::{self, Ordering};
 use core::fmt;
 use core::hash::{Hash, Hasher};
@@ -1512,7 +1511,7 @@ impl<T> VecDeque<T> {
     /// Removes an element from anywhere in the `VecDeque` and returns it,
     /// replacing it with the first element.
     ///
-    /// This does not preserve ordering, but is `O(1)`.
+    /// This does not preserve ordering, but is *O*(1).
     ///
     /// Returns `None` if `index` is out of bounds.
     ///
@@ -1547,7 +1546,7 @@ impl<T> VecDeque<T> {
     /// Removes an element from anywhere in the `VecDeque` and returns it, replacing it with the
     /// last element.
     ///
-    /// This does not preserve ordering, but is `O(1)`.
+    /// This does not preserve ordering, but is *O*(1).
     ///
     /// Returns `None` if `index` is out of bounds.
     ///
@@ -2331,7 +2330,7 @@ impl<T> VecDeque<T> {
     ///
     /// # Complexity
     ///
-    /// Takes `O(min(mid, len() - mid))` time and no extra space.
+    /// Takes `*O*(min(mid, len() - mid))` time and no extra space.
     ///
     /// # Examples
     ///
@@ -2374,7 +2373,7 @@ impl<T> VecDeque<T> {
     ///
     /// # Complexity
     ///
-    /// Takes `O(min(k, len() - k))` time and no extra space.
+    /// Takes `*O*(min(k, len() - k))` time and no extra space.
     ///
     /// # Examples
     ///
@@ -2889,9 +2888,9 @@ macro_rules! __impl_slice_eq1 {
 __impl_slice_eq1! { [] VecDeque<A>, Vec<B>, }
 __impl_slice_eq1! { [] VecDeque<A>, &[B], }
 __impl_slice_eq1! { [] VecDeque<A>, &mut [B], }
-__impl_slice_eq1! { [const N: usize] VecDeque<A>, [B; N], [B; N]: LengthAtMost32 }
+__impl_slice_eq1! { [const N: usize] VecDeque<A>, [B; N], }
-__impl_slice_eq1! { [const N: usize] VecDeque<A>, &[B; N], [B; N]: LengthAtMost32 }
+__impl_slice_eq1! { [const N: usize] VecDeque<A>, &[B; N], }
-__impl_slice_eq1! { [const N: usize] VecDeque<A>, &mut [B; N], [B; N]: LengthAtMost32 }
+__impl_slice_eq1! { [const N: usize] VecDeque<A>, &mut [B; N], }
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<A: PartialOrd> PartialOrd for VecDeque<A> {
@@ -3076,7 +3075,7 @@ impl<T> From<VecDeque<T>> for Vec<T> {
     /// [`Vec<T>`]: crate::vec::Vec
     /// [`VecDeque<T>`]: crate::collections::VecDeque
     ///
-    /// This never needs to re-allocate, but does need to do `O(n)` data movement if
+    /// This never needs to re-allocate, but does need to do *O*(*n*) data movement if
     /// the circular buffer doesn't happen to be at the beginning of the allocation.
     ///
     /// # Examples
@@ -3084,7 +3083,7 @@ impl<T> From<VecDeque<T>> for Vec<T> {
     /// ```
     /// use std::collections::VecDeque;
     ///
-    /// // This one is O(1).
+    /// // This one is *O*(1).
     /// let deque: VecDeque<_> = (1..5).collect();
     /// let ptr = deque.as_slices().0.as_ptr();
     /// let vec = Vec::from(deque);

library/alloc/src/collections/vec_deque/tests.rs

@@ -0,0 +1,572 @@
+use super::*;
+
+#[bench]
+#[cfg_attr(miri, ignore)] // isolated Miri does not support benchmarks
+fn bench_push_back_100(b: &mut test::Bencher) {
+    let mut deq = VecDeque::with_capacity(101);
+    b.iter(|| {
+        for i in 0..100 {
+            deq.push_back(i);
+        }
+        deq.head = 0;
+        deq.tail = 0;
+    })
+}
+
+#[bench]
+#[cfg_attr(miri, ignore)] // isolated Miri does not support benchmarks
+fn bench_push_front_100(b: &mut test::Bencher) {
+    let mut deq = VecDeque::with_capacity(101);
+    b.iter(|| {
+        for i in 0..100 {
+            deq.push_front(i);
+        }
+        deq.head = 0;
+        deq.tail = 0;
+    })
+}
+
+#[bench]
+#[cfg_attr(miri, ignore)] // isolated Miri does not support benchmarks
+fn bench_pop_back_100(b: &mut test::Bencher) {
+    let mut deq = VecDeque::<i32>::with_capacity(101);
+
+    b.iter(|| {
+        deq.head = 100;
+        deq.tail = 0;
+        while !deq.is_empty() {
+            test::black_box(deq.pop_back());
+        }
+    })
+}
+
+#[bench]
+#[cfg_attr(miri, ignore)] // isolated Miri does not support benchmarks
+fn bench_pop_front_100(b: &mut test::Bencher) {
+    let mut deq = VecDeque::<i32>::with_capacity(101);
+
+    b.iter(|| {
+        deq.head = 100;
+        deq.tail = 0;
+        while !deq.is_empty() {
+            test::black_box(deq.pop_front());
+        }
+    })
+}
+
+#[test]
+fn test_swap_front_back_remove() {
+    fn test(back: bool) {
+        // This test checks that every single combination of tail position and length is tested.
+        // Capacity 15 should be large enough to cover every case.
+        let mut tester = VecDeque::with_capacity(15);
+        let usable_cap = tester.capacity();
+        let final_len = usable_cap / 2;
+
+        for len in 0..final_len {
+            let expected: VecDeque<_> =
+                if back { (0..len).collect() } else { (0..len).rev().collect() };
+            for tail_pos in 0..usable_cap {
+                tester.tail = tail_pos;
+                tester.head = tail_pos;
+                if back {
+                    for i in 0..len * 2 {
+                        tester.push_front(i);
+                    }
+                    for i in 0..len {
+                        assert_eq!(tester.swap_remove_back(i), Some(len * 2 - 1 - i));
+                    }
+                } else {
+                    for i in 0..len * 2 {
+                        tester.push_back(i);
+                    }
+                    for i in 0..len {
+                        let idx = tester.len() - 1 - i;
+                        assert_eq!(tester.swap_remove_front(idx), Some(len * 2 - 1 - i));
+                    }
+                }
+                assert!(tester.tail < tester.cap());
+                assert!(tester.head < tester.cap());
+                assert_eq!(tester, expected);
+            }
+        }
+    }
+    test(true);
+    test(false);
+}
+
+#[test]
+fn test_insert() {
+    // This test checks that every single combination of tail position, length, and
+    // insertion position is tested. Capacity 15 should be large enough to cover every case.
+
+    let mut tester = VecDeque::with_capacity(15);
+    // can't guarantee we got 15, so have to get what we got.
+    // 15 would be great, but we will definitely get 2^k - 1, for k >= 4, or else
+    // this test isn't covering what it wants to
+    let cap = tester.capacity();
+
+    // len is the length *after* insertion
+    let minlen = if cfg!(miri) { cap - 1 } else { 1 }; // Miri is too slow
+    for len in minlen..cap {
+        // 0, 1, 2, .., len - 1
+        let expected = (0..).take(len).collect::<VecDeque<_>>();
+        for tail_pos in 0..cap {
+            for to_insert in 0..len {
+                tester.tail = tail_pos;
+                tester.head = tail_pos;
+                for i in 0..len {
+                    if i != to_insert {
+                        tester.push_back(i);
+                    }
+                }
+                tester.insert(to_insert, to_insert);
+                assert!(tester.tail < tester.cap());
+                assert!(tester.head < tester.cap());
+                assert_eq!(tester, expected);
+            }
+        }
+    }
+}
+
+#[test]
+fn make_contiguous_big_tail() {
+    let mut tester = VecDeque::with_capacity(15);
+
+    for i in 0..3 {
+        tester.push_back(i);
+    }
+
+    for i in 3..10 {
+        tester.push_front(i);
+    }
+
+    // 012......9876543
+    assert_eq!(tester.capacity(), 15);
+    assert_eq!((&[9, 8, 7, 6, 5, 4, 3] as &[_], &[0, 1, 2] as &[_]), tester.as_slices());
+
+    let expected_start = tester.head;
+    tester.make_contiguous();
+    assert_eq!(tester.tail, expected_start);
+    assert_eq!((&[9, 8, 7, 6, 5, 4, 3, 0, 1, 2] as &[_], &[] as &[_]), tester.as_slices());
+}
+
+#[test]
+fn make_contiguous_big_head() {
+    let mut tester = VecDeque::with_capacity(15);
+
+    for i in 0..8 {
+        tester.push_back(i);
+    }
+
+    for i in 8..10 {
+        tester.push_front(i);
+    }
+
+    // 01234567......98
+    let expected_start = 0;
+    tester.make_contiguous();
+    assert_eq!(tester.tail, expected_start);
+    assert_eq!((&[9, 8, 0, 1, 2, 3, 4, 5, 6, 7] as &[_], &[] as &[_]), tester.as_slices());
+}
+
+#[test]
+fn make_contiguous_small_free() {
+    let mut tester = VecDeque::with_capacity(15);
+
+    for i in 'A' as u8..'I' as u8 {
+        tester.push_back(i as char);
+    }
+
+    for i in 'I' as u8..'N' as u8 {
+        tester.push_front(i as char);
+    }
+
+    // ABCDEFGH...MLKJI
+    let expected_start = 0;
+    tester.make_contiguous();
+    assert_eq!(tester.tail, expected_start);
+    assert_eq!(
+        (&['M', 'L', 'K', 'J', 'I', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H'] as &[_], &[] as &[_]),
+        tester.as_slices()
+    );
+
+    tester.clear();
+    for i in 'I' as u8..'N' as u8 {
+        tester.push_back(i as char);
+    }
+
+    for i in 'A' as u8..'I' as u8 {
+        tester.push_front(i as char);
+    }
+
+    // IJKLM...HGFEDCBA
+    let expected_start = 0;
+    tester.make_contiguous();
+    assert_eq!(tester.tail, expected_start);
+    assert_eq!(
+        (&['H', 'G', 'F', 'E', 'D', 'C', 'B', 'A', 'I', 'J', 'K', 'L', 'M'] as &[_], &[] as &[_]),
+        tester.as_slices()
+    );
+}
+
+#[test]
+fn test_remove() {
+    // This test checks that every single combination of tail position, length, and
+    // removal position is tested. Capacity 15 should be large enough to cover every case.
+
+    let mut tester = VecDeque::with_capacity(15);
+    // can't guarantee we got 15, so have to get what we got.
+    // 15 would be great, but we will definitely get 2^k - 1, for k >= 4, or else
+    // this test isn't covering what it wants to
+    let cap = tester.capacity();
+
+    // len is the length *after* removal
+    let minlen = if cfg!(miri) { cap - 2 } else { 0 }; // Miri is too slow
+    for len in minlen..cap - 1 {
+        // 0, 1, 2, .., len - 1
+        let expected = (0..).take(len).collect::<VecDeque<_>>();
+        for tail_pos in 0..cap {
+            for to_remove in 0..=len {
+                tester.tail = tail_pos;
+                tester.head = tail_pos;
+                for i in 0..len {
+                    if i == to_remove {
+                        tester.push_back(1234);
+                    }
+                    tester.push_back(i);
+                }
+                if to_remove == len {
+                    tester.push_back(1234);
+                }
+                tester.remove(to_remove);
+                assert!(tester.tail < tester.cap());
+                assert!(tester.head < tester.cap());
+                assert_eq!(tester, expected);
+            }
+        }
+    }
+}
+
+#[test]
+fn test_range() {
+    let mut tester: VecDeque<usize> = VecDeque::with_capacity(7);
+
+    let cap = tester.capacity();
+    let minlen = if cfg!(miri) { cap - 1 } else { 0 }; // Miri is too slow
+    for len in minlen..=cap {
+        for tail in 0..=cap {
+            for start in 0..=len {
+                for end in start..=len {
+                    tester.tail = tail;
+                    tester.head = tail;
+                    for i in 0..len {
+                        tester.push_back(i);
+                    }
+
+                    // Check that we iterate over the correct values
+                    let range: VecDeque<_> = tester.range(start..end).copied().collect();
+                    let expected: VecDeque<_> = (start..end).collect();
+                    assert_eq!(range, expected);
+                }
+            }
+        }
+    }
+}
+
+#[test]
+fn test_range_mut() {
+    let mut tester: VecDeque<usize> = VecDeque::with_capacity(7);
+
+    let cap = tester.capacity();
+    for len in 0..=cap {
+        for tail in 0..=cap {
+            for start in 0..=len {
+                for end in start..=len {
+                    tester.tail = tail;
+                    tester.head = tail;
+                    for i in 0..len {
+                        tester.push_back(i);
+                    }
+
+                    let head_was = tester.head;
+                    let tail_was = tester.tail;
+
+                    // Check that we iterate over the correct values
+                    let range: VecDeque<_> = tester.range_mut(start..end).map(|v| *v).collect();
+                    let expected: VecDeque<_> = (start..end).collect();
+                    assert_eq!(range, expected);
+
+                    // We shouldn't have changed the capacity or made the
+                    // head or tail out of bounds
+                    assert_eq!(tester.capacity(), cap);
+                    assert_eq!(tester.tail, tail_was);
+                    assert_eq!(tester.head, head_was);
+                }
+            }
+        }
+    }
+}
+
+#[test]
+fn test_drain() {
+    let mut tester: VecDeque<usize> = VecDeque::with_capacity(7);
+
+    let cap = tester.capacity();
+    for len in 0..=cap {
+        for tail in 0..=cap {
+            for drain_start in 0..=len {
+                for drain_end in drain_start..=len {
+                    tester.tail = tail;
+                    tester.head = tail;
+                    for i in 0..len {
+                        tester.push_back(i);
+                    }
+
+                    // Check that we drain the correct values
+                    let drained: VecDeque<_> = tester.drain(drain_start..drain_end).collect();
+                    let drained_expected: VecDeque<_> = (drain_start..drain_end).collect();
+                    assert_eq!(drained, drained_expected);
+
+                    // We shouldn't have changed the capacity or made the
+                    // head or tail out of bounds
+                    assert_eq!(tester.capacity(), cap);
+                    assert!(tester.tail < tester.cap());
+                    assert!(tester.head < tester.cap());
+
+                    // We should see the correct values in the VecDeque
+                    let expected: VecDeque<_> = (0..drain_start).chain(drain_end..len).collect();
+                    assert_eq!(expected, tester);
+                }
+            }
+        }
+    }
+}
+
+#[test]
+fn test_shrink_to_fit() {
+    // This test checks that every single combination of head and tail position,
+    // is tested. Capacity 15 should be large enough to cover every case.
+
+    let mut tester = VecDeque::with_capacity(15);
+    // can't guarantee we got 15, so have to get what we got.
+    // 15 would be great, but we will definitely get 2^k - 1, for k >= 4, or else
+    // this test isn't covering what it wants to
+    let cap = tester.capacity();
+    tester.reserve(63);
+    let max_cap = tester.capacity();
+
+    for len in 0..=cap {
+        // 0, 1, 2, .., len - 1
+        let expected = (0..).take(len).collect::<VecDeque<_>>();
+        for tail_pos in 0..=max_cap {
+            tester.tail = tail_pos;
+            tester.head = tail_pos;
+            tester.reserve(63);
+            for i in 0..len {
+                tester.push_back(i);
+            }
+            tester.shrink_to_fit();
+            assert!(tester.capacity() <= cap);
+            assert!(tester.tail < tester.cap());
+            assert!(tester.head < tester.cap());
+            assert_eq!(tester, expected);
+        }
+    }
+}
+
+#[test]
+fn test_split_off() {
+    // This test checks that every single combination of tail position, length, and
+    // split position is tested. Capacity 15 should be large enough to cover every case.
+
+    let mut tester = VecDeque::with_capacity(15);
+    // can't guarantee we got 15, so have to get what we got.
+    // 15 would be great, but we will definitely get 2^k - 1, for k >= 4, or else
+    // this test isn't covering what it wants to
+    let cap = tester.capacity();
+
+    // len is the length *before* splitting
+    let minlen = if cfg!(miri) { cap - 1 } else { 0 }; // Miri is too slow
+    for len in minlen..cap {
+        // index to split at
+        for at in 0..=len {
+            // 0, 1, 2, .., at - 1 (may be empty)
+            let expected_self = (0..).take(at).collect::<VecDeque<_>>();
+            // at, at + 1, .., len - 1 (may be empty)
+            let expected_other = (at..).take(len - at).collect::<VecDeque<_>>();
+
+            for tail_pos in 0..cap {
+                tester.tail = tail_pos;
+                tester.head = tail_pos;
+                for i in 0..len {
+                    tester.push_back(i);
+                }
+                let result = tester.split_off(at);
+                assert!(tester.tail < tester.cap());
+                assert!(tester.head < tester.cap());
+                assert!(result.tail < result.cap());
+                assert!(result.head < result.cap());
+                assert_eq!(tester, expected_self);
+                assert_eq!(result, expected_other);
+            }
+        }
+    }
+}
+
+#[test]
+fn test_from_vec() {
+    use crate::vec::Vec;
+    for cap in 0..35 {
+        for len in 0..=cap {
+            let mut vec = Vec::with_capacity(cap);
+            vec.extend(0..len);
+
+            let vd = VecDeque::from(vec.clone());
+            assert!(vd.cap().is_power_of_two());
+            assert_eq!(vd.len(), vec.len());
+            assert!(vd.into_iter().eq(vec));
+        }
+    }
+}
+
+#[test]
+fn test_vec_from_vecdeque() {
+    use crate::vec::Vec;
+
+    fn create_vec_and_test_convert(capacity: usize, offset: usize, len: usize) {
+        let mut vd = VecDeque::with_capacity(capacity);
+        for _ in 0..offset {
+            vd.push_back(0);
+            vd.pop_front();
+        }
+        vd.extend(0..len);
+
+        let vec: Vec<_> = Vec::from(vd.clone());
+        assert_eq!(vec.len(), vd.len());
+        assert!(vec.into_iter().eq(vd));
+    }
+
+    // Miri is too slow
+    let max_pwr = if cfg!(miri) { 5 } else { 7 };
+
+    for cap_pwr in 0..max_pwr {
+        // Make capacity as a (2^x)-1, so that the ring size is 2^x
+        let cap = (2i32.pow(cap_pwr) - 1) as usize;
+
+        // In these cases there is enough free space to solve it with copies
+        for len in 0..((cap + 1) / 2) {
+            // Test contiguous cases
+            for offset in 0..(cap - len) {
+                create_vec_and_test_convert(cap, offset, len)
+            }
+
+            // Test cases where block at end of buffer is bigger than block at start
+            for offset in (cap - len)..(cap - (len / 2)) {
+                create_vec_and_test_convert(cap, offset, len)
+            }
+
+            // Test cases where block at start of buffer is bigger than block at end
+            for offset in (cap - (len / 2))..cap {
+                create_vec_and_test_convert(cap, offset, len)
+            }
+        }
+
+        // Now there's not (necessarily) space to straighten the ring with simple copies,
+        // the ring will use swapping when:
+        // (cap + 1 - offset) > (cap + 1 - len) && (len - (cap + 1 - offset)) > (cap + 1 - len))
+        //  right block size  >   free space    &&      left block size       >    free space
+        for len in ((cap + 1) / 2)..cap {
+            // Test contiguous cases
+            for offset in 0..(cap - len) {
+                create_vec_and_test_convert(cap, offset, len)
+            }
+
+            // Test cases where block at end of buffer is bigger than block at start
+            for offset in (cap - len)..(cap - (len / 2)) {
+                create_vec_and_test_convert(cap, offset, len)
+            }
+
+            // Test cases where block at start of buffer is bigger than block at end
+            for offset in (cap - (len / 2))..cap {
+                create_vec_and_test_convert(cap, offset, len)
+            }
+        }
+    }
+}
+
+#[test]
+fn test_clone_from() {
+    let m = vec![1; 8];
+    let n = vec![2; 12];
+    let limit = if cfg!(miri) { 4 } else { 8 }; // Miri is too slow
+    for pfv in 0..limit {
+        for pfu in 0..limit {
+            for longer in 0..2 {
+                let (vr, ur) = if longer == 0 { (&m, &n) } else { (&n, &m) };
+                let mut v = VecDeque::from(vr.clone());
+                for _ in 0..pfv {
+                    v.push_front(1);
+                }
+                let mut u = VecDeque::from(ur.clone());
+                for _ in 0..pfu {
+                    u.push_front(2);
+                }
+                v.clone_from(&u);
+                assert_eq!(&v, &u);
+            }
+        }
+    }
+}
+
+#[test]
+fn test_vec_deque_truncate_drop() {
+    static mut DROPS: u32 = 0;
+    #[derive(Clone)]
+    struct Elem(i32);
+    impl Drop for Elem {
+        fn drop(&mut self) {
+            unsafe {
+                DROPS += 1;
+            }
+        }
+    }
+
+    let v = vec![Elem(1), Elem(2), Elem(3), Elem(4), Elem(5)];
+    for push_front in 0..=v.len() {
+        let v = v.clone();
+        let mut tester = VecDeque::with_capacity(5);
+        for (index, elem) in v.into_iter().enumerate() {
+            if index < push_front {
+                tester.push_front(elem);
+            } else {
+                tester.push_back(elem);
+            }
+        }
+        assert_eq!(unsafe { DROPS }, 0);
+        tester.truncate(3);
+        assert_eq!(unsafe { DROPS }, 2);
+        tester.truncate(0);
+        assert_eq!(unsafe { DROPS }, 5);
+        unsafe {
+            DROPS = 0;
+        }
+    }
+}
+
+#[test]
+fn issue_53529() {
+    use crate::boxed::Box;
+
+    let mut dst = VecDeque::new();
+    dst.push_front(Box::new(1));
+    dst.push_front(Box::new(2));
+    assert_eq!(*dst.pop_back().unwrap(), 1);
+
+    let mut src = VecDeque::new();
+    src.push_front(Box::new(2));
+    dst.append(&mut src);
+    for a in dst {
+        assert_eq!(*a, 2);
+    }
+}

library/alloc/src/fmt.rs

@@ -0,0 +1,579 @@
+//! Utilities for formatting and printing `String`s.
+//!
+//! This module contains the runtime support for the [`format!`] syntax extension.
+//! This macro is implemented in the compiler to emit calls to this module in
+//! order to format arguments at runtime into strings.
+//!
+//! # Usage
+//!
+//! The [`format!`] macro is intended to be familiar to those coming from C's
+//! `printf`/`fprintf` functions or Python's `str.format` function.
+//!
+//! Some examples of the [`format!`] extension are:
+//!
+//! ```
+//! format!("Hello");                 // => "Hello"
+//! format!("Hello, {}!", "world");   // => "Hello, world!"
+//! format!("The number is {}", 1);   // => "The number is 1"
+//! format!("{:?}", (3, 4));          // => "(3, 4)"
+//! format!("{value}", value=4);      // => "4"
+//! format!("{} {}", 1, 2);           // => "1 2"
+//! format!("{:04}", 42);             // => "0042" with leading zeros
+//! ```
+//!
+//! From these, you can see that the first argument is a format string. It is
+//! required by the compiler for this to be a string literal; it cannot be a
+//! variable passed in (in order to perform validity checking). The compiler
+//! will then parse the format string and determine if the list of arguments
+//! provided is suitable to pass to this format string.
+//!
+//! To convert a single value to a string, use the [`to_string`] method. This
+//! will use the [`Display`] formatting trait.
+//!
+//! ## Positional parameters
+//!
+//! Each formatting argument is allowed to specify which value argument it's
+//! referencing, and if omitted it is assumed to be "the next argument". For
+//! example, the format string `{} {} {}` would take three parameters, and they
+//! would be formatted in the same order as they're given. The format string
+//! `{2} {1} {0}`, however, would format arguments in reverse order.
+//!
+//! Things can get a little tricky once you start intermingling the two types of
+//! positional specifiers. The "next argument" specifier can be thought of as an
+//! iterator over the argument. Each time a "next argument" specifier is seen,
+//! the iterator advances. This leads to behavior like this:
+//!
+//! ```
+//! format!("{1} {} {0} {}", 1, 2); // => "2 1 1 2"
+//! ```
+//!
+//! The internal iterator over the argument has not been advanced by the time
+//! the first `{}` is seen, so it prints the first argument. Then upon reaching
+//! the second `{}`, the iterator has advanced forward to the second argument.
+//! Essentially, parameters that explicitly name their argument do not affect
+//! parameters that do not name an argument in terms of positional specifiers.
+//!
+//! A format string is required to use all of its arguments, otherwise it is a
+//! compile-time error. You may refer to the same argument more than once in the
+//! format string.
+//!
+//! ## Named parameters
+//!
+//! Rust itself does not have a Python-like equivalent of named parameters to a
+//! function, but the [`format!`] macro is a syntax extension that allows it to
+//! leverage named parameters. Named parameters are listed at the end of the
+//! argument list and have the syntax:
+//!
+//! ```text
+//! identifier '=' expression
+//! ```
+//!
+//! For example, the following [`format!`] expressions all use named argument:
+//!
+//! ```
+//! format!("{argument}", argument = "test");   // => "test"
+//! format!("{name} {}", 1, name = 2);          // => "2 1"
+//! format!("{a} {c} {b}", a="a", b='b', c=3);  // => "a 3 b"
+//! ```
+//!
+//! It is not valid to put positional parameters (those without names) after
+//! arguments that have names. Like with positional parameters, it is not
+//! valid to provide named parameters that are unused by the format string.
+//!
+//! # Formatting Parameters
+//!
+//! Each argument being formatted can be transformed by a number of formatting
+//! parameters (corresponding to `format_spec` in [the syntax](#syntax)). These
+//! parameters affect the string representation of what's being formatted.
+//!
+//! ## Width
+//!
+//! ```
+//! // All of these print "Hello x    !"
+//! println!("Hello {:5}!", "x");
+//! println!("Hello {:1$}!", "x", 5);
+//! println!("Hello {1:0$}!", 5, "x");
+//! println!("Hello {:width$}!", "x", width = 5);
+//! ```
+//!
+//! This is a parameter for the "minimum width" that the format should take up.
+//! If the value's string does not fill up this many characters, then the
+//! padding specified by fill/alignment will be used to take up the required
+//! space (see below).
+//!
+//! The value for the width can also be provided as a [`usize`] in the list of
+//! parameters by adding a postfix `$`, indicating that the second argument is
+//! a [`usize`] specifying the width.
+//!
+//! Referring to an argument with the dollar syntax does not affect the "next
+//! argument" counter, so it's usually a good idea to refer to arguments by
+//! position, or use named arguments.
+//!
+//! ## Fill/Alignment
+//!
+//! ```
+//! assert_eq!(format!("Hello {:<5}!", "x"),  "Hello x    !");
+//! assert_eq!(format!("Hello {:-<5}!", "x"), "Hello x----!");
+//! assert_eq!(format!("Hello {:^5}!", "x"),  "Hello   x  !");
+//! assert_eq!(format!("Hello {:>5}!", "x"),  "Hello     x!");
+//! ```
+//!
+//! The optional fill character and alignment is provided normally in conjunction with the
+//! [`width`](#width) parameter. It must be defined before `width`, right after the `:`.
+//! This indicates that if the value being formatted is smaller than
+//! `width` some extra characters will be printed around it.
+//! Filling comes in the following variants for different alignments:
+//!
+//! * `[fill]<` - the argument is left-aligned in `width` columns
+//! * `[fill]^` - the argument is center-aligned in `width` columns
+//! * `[fill]>` - the argument is right-aligned in `width` columns
+//!
+//! The default [fill/alignment](#fillalignment) for non-numerics is a space and
+//! left-aligned. The
+//! default for numeric formatters is also a space character but with right-alignment. If
+//! the `0` flag (see below) is specified for numerics, then the implicit fill character is
+//! `0`.
+//!
+//! Note that alignment may not be implemented by some types. In particular, it
+//! is not generally implemented for the `Debug` trait.  A good way to ensure
+//! padding is applied is to format your input, then pad this resulting string
+//! to obtain your output:
+//!
+//! ```
+//! println!("Hello {:^15}!", format!("{:?}", Some("hi"))); // => "Hello   Some("hi")   !"
+//! ```
+//!
+//! ## Sign/`#`/`0`
+//!
+//! ```
+//! assert_eq!(format!("Hello {:+}!", 5), "Hello +5!");
+//! assert_eq!(format!("{:#x}!", 27), "0x1b!");
+//! assert_eq!(format!("Hello {:05}!", 5),  "Hello 00005!");
+//! assert_eq!(format!("Hello {:05}!", -5), "Hello -0005!");
+//! assert_eq!(format!("{:#010x}!", 27), "0x0000001b!");
+//! ```
+//!
+//! These are all flags altering the behavior of the formatter.
+//!
+//! * `+` - This is intended for numeric types and indicates that the sign
+//!         should always be printed. Positive signs are never printed by
+//!         default, and the negative sign is only printed by default for the
+//!         `Signed` trait. This flag indicates that the correct sign (`+` or `-`)
+//!         should always be printed.
+//! * `-` - Currently not used
+//! * `#` - This flag indicates that the "alternate" form of printing should
+//!         be used. The alternate forms are:
+//!     * `#?` - pretty-print the [`Debug`] formatting
+//!     * `#x` - precedes the argument with a `0x`
+//!     * `#X` - precedes the argument with a `0x`
+//!     * `#b` - precedes the argument with a `0b`
+//!     * `#o` - precedes the argument with a `0o`
+//! * `0` - This is used to indicate for integer formats that the padding to `width` should
+//!         both be done with a `0` character as well as be sign-aware. A format
+//!         like `{:08}` would yield `00000001` for the integer `1`, while the
+//!         same format would yield `-0000001` for the integer `-1`. Notice that
+//!         the negative version has one fewer zero than the positive version.
+//!         Note that padding zeros are always placed after the sign (if any)
+//!         and before the digits. When used together with the `#` flag, a similar
+//!         rule applies: padding zeros are inserted after the prefix but before
+//!         the digits. The prefix is included in the total width.
+//!
+//! ## Precision
+//!
+//! For non-numeric types, this can be considered a "maximum width". If the resulting string is
+//! longer than this width, then it is truncated down to this many characters and that truncated
+//! value is emitted with proper `fill`, `alignment` and `width` if those parameters are set.
+//!
+//! For integral types, this is ignored.
+//!
+//! For floating-point types, this indicates how many digits after the decimal point should be
+//! printed.
+//!
+//! There are three possible ways to specify the desired `precision`:
+//!
+//! 1. An integer `.N`:
+//!
+//!    the integer `N` itself is the precision.
+//!
+//! 2. An integer or name followed by dollar sign `.N$`:
+//!
+//!    use format *argument* `N` (which must be a `usize`) as the precision.
+//!
+//! 3. An asterisk `.*`:
+//!
+//!    `.*` means that this `{...}` is associated with *two* format inputs rather than one: the
+//!    first input holds the `usize` precision, and the second holds the value to print. Note that
+//!    in this case, if one uses the format string `{<arg>:<spec>.*}`, then the `<arg>` part refers
+//!    to the *value* to print, and the `precision` must come in the input preceding `<arg>`.
+//!
+//! For example, the following calls all print the same thing `Hello x is 0.01000`:
+//!
+//! ```
+//! // Hello {arg 0 ("x")} is {arg 1 (0.01) with precision specified inline (5)}
+//! println!("Hello {0} is {1:.5}", "x", 0.01);
+//!
+//! // Hello {arg 1 ("x")} is {arg 2 (0.01) with precision specified in arg 0 (5)}
+//! println!("Hello {1} is {2:.0$}", 5, "x", 0.01);
+//!
+//! // Hello {arg 0 ("x")} is {arg 2 (0.01) with precision specified in arg 1 (5)}
+//! println!("Hello {0} is {2:.1$}", "x", 5, 0.01);
+//!
+//! // Hello {next arg ("x")} is {second of next two args (0.01) with precision
+//! //                          specified in first of next two args (5)}
+//! println!("Hello {} is {:.*}",    "x", 5, 0.01);
+//!
+//! // Hello {next arg ("x")} is {arg 2 (0.01) with precision
+//! //                          specified in its predecessor (5)}
+//! println!("Hello {} is {2:.*}",   "x", 5, 0.01);
+//!
+//! // Hello {next arg ("x")} is {arg "number" (0.01) with precision specified
+//! //                          in arg "prec" (5)}
+//! println!("Hello {} is {number:.prec$}", "x", prec = 5, number = 0.01);
+//! ```
+//!
+//! While these:
+//!
+//! ```
+//! println!("{}, `{name:.*}` has 3 fractional digits", "Hello", 3, name=1234.56);
+//! println!("{}, `{name:.*}` has 3 characters", "Hello", 3, name="1234.56");
+//! println!("{}, `{name:>8.*}` has 3 right-aligned characters", "Hello", 3, name="1234.56");
+//! ```
+//!
+//! print three significantly different things:
+//!
+//! ```text
+//! Hello, `1234.560` has 3 fractional digits
+//! Hello, `123` has 3 characters
+//! Hello, `     123` has 3 right-aligned characters
+//! ```
+//!
+//! ## Localization
+//!
+//! In some programming languages, the behavior of string formatting functions
+//! depends on the operating system's locale setting. The format functions
+//! provided by Rust's standard library do not have any concept of locale and
+//! will produce the same results on all systems regardless of user
+//! configuration.
+//!
+//! For example, the following code will always print `1.5` even if the system
+//! locale uses a decimal separator other than a dot.
+//!
+//! ```
+//! println!("The value is {}", 1.5);
+//! ```
+//!
+//! # Escaping
+//!
+//! The literal characters `{` and `}` may be included in a string by preceding
+//! them with the same character. For example, the `{` character is escaped with
+//! `{{` and the `}` character is escaped with `}}`.
+//!
+//! ```
+//! assert_eq!(format!("Hello {{}}"), "Hello {}");
+//! assert_eq!(format!("{{ Hello"), "{ Hello");
+//! ```
+//!
+//! # Syntax
+//!
+//! To summarize, here you can find the full grammar of format strings.
+//! The syntax for the formatting language used is drawn from other languages,
+//! so it should not be too alien. Arguments are formatted with Python-like
+//! syntax, meaning that arguments are surrounded by `{}` instead of the C-like
+//! `%`. The actual grammar for the formatting syntax is:
+//!
+//! ```text
+//! format_string := <text> [ maybe-format <text> ] *
+//! maybe-format := '{' '{' | '}' '}' | <format>
+//! format := '{' [ argument ] [ ':' format_spec ] '}'
+//! argument := integer | identifier
+//!
+//! format_spec := [[fill]align][sign]['#']['0'][width]['.' precision][type]
+//! fill := character
+//! align := '<' | '^' | '>'
+//! sign := '+' | '-'
+//! width := count
+//! precision := count | '*'
+//! type := identifier | '?' | ''
+//! count := parameter | integer
+//! parameter := argument '$'
+//! ```
+//!
+//! # Formatting traits
+//!
+//! When requesting that an argument be formatted with a particular type, you
+//! are actually requesting that an argument ascribes to a particular trait.
+//! This allows multiple actual types to be formatted via `{:x}` (like [`i8`] as
+//! well as [`isize`]). The current mapping of types to traits is:
+//!
+//! * *nothing* ⇒ [`Display`]
+//! * `?` ⇒ [`Debug`]
+//! * `x?` ⇒ [`Debug`] with lower-case hexadecimal integers
+//! * `X?` ⇒ [`Debug`] with upper-case hexadecimal integers
+//! * `o` ⇒ [`Octal`](trait.Octal.html)
+//! * `x` ⇒ [`LowerHex`](trait.LowerHex.html)
+//! * `X` ⇒ [`UpperHex`](trait.UpperHex.html)
+//! * `p` ⇒ [`Pointer`](trait.Pointer.html)
+//! * `b` ⇒ [`Binary`]
+//! * `e` ⇒ [`LowerExp`](trait.LowerExp.html)
+//! * `E` ⇒ [`UpperExp`](trait.UpperExp.html)
+//!
+//! What this means is that any type of argument which implements the
+//! [`fmt::Binary`][`Binary`] trait can then be formatted with `{:b}`. Implementations
+//! are provided for these traits for a number of primitive types by the
+//! standard library as well. If no format is specified (as in `{}` or `{:6}`),
+//! then the format trait used is the [`Display`] trait.
+//!
+//! When implementing a format trait for your own type, you will have to
+//! implement a method of the signature:
+//!
+//! ```
+//! # #![allow(dead_code)]
+//! # use std::fmt;
+//! # struct Foo; // our custom type
+//! # impl fmt::Display for Foo {
+//! fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+//! # write!(f, "testing, testing")
+//! # } }
+//! ```
+//!
+//! Your type will be passed as `self` by-reference, and then the function
+//! should emit output into the `f.buf` stream. It is up to each format trait
+//! implementation to correctly adhere to the requested formatting parameters.
+//! The values of these parameters will be listed in the fields of the
+//! [`Formatter`] struct. In order to help with this, the [`Formatter`] struct also
+//! provides some helper methods.
+//!
+//! Additionally, the return value of this function is [`fmt::Result`] which is a
+//! type alias of [`Result`]`<(), `[`std::fmt::Error`]`>`. Formatting implementations
+//! should ensure that they propagate errors from the [`Formatter`] (e.g., when
+//! calling [`write!`]). However, they should never return errors spuriously. That
+//! is, a formatting implementation must and may only return an error if the
+//! passed-in [`Formatter`] returns an error. This is because, contrary to what
+//! the function signature might suggest, string formatting is an infallible
+//! operation. This function only returns a result because writing to the
+//! underlying stream might fail and it must provide a way to propagate the fact
+//! that an error has occurred back up the stack.
+//!
+//! An example of implementing the formatting traits would look
+//! like:
+//!
+//! ```
+//! use std::fmt;
+//!
+//! #[derive(Debug)]
+//! struct Vector2D {
+//!     x: isize,
+//!     y: isize,
+//! }
+//!
+//! impl fmt::Display for Vector2D {
+//!     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+//!         // The `f` value implements the `Write` trait, which is what the
+//!         // write! macro is expecting. Note that this formatting ignores the
+//!         // various flags provided to format strings.
+//!         write!(f, "({}, {})", self.x, self.y)
+//!     }
+//! }
+//!
+//! // Different traits allow different forms of output of a type. The meaning
+//! // of this format is to print the magnitude of a vector.
+//! impl fmt::Binary for Vector2D {
+//!     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+//!         let magnitude = (self.x * self.x + self.y * self.y) as f64;
+//!         let magnitude = magnitude.sqrt();
+//!
+//!         // Respect the formatting flags by using the helper method
+//!         // `pad_integral` on the Formatter object. See the method
+//!         // documentation for details, and the function `pad` can be used
+//!         // to pad strings.
+//!         let decimals = f.precision().unwrap_or(3);
+//!         let string = format!("{:.*}", decimals, magnitude);
+//!         f.pad_integral(true, "", &string)
+//!     }
+//! }
+//!
+//! fn main() {
+//!     let myvector = Vector2D { x: 3, y: 4 };
+//!
+//!     println!("{}", myvector);       // => "(3, 4)"
+//!     println!("{:?}", myvector);     // => "Vector2D {x: 3, y:4}"
+//!     println!("{:10.3b}", myvector); // => "     5.000"
+//! }
+//! ```
+//!
+//! ### `fmt::Display` vs `fmt::Debug`
+//!
+//! These two formatting traits have distinct purposes:
+//!
+//! - [`fmt::Display`][`Display`] implementations assert that the type can be faithfully
+//!   represented as a UTF-8 string at all times. It is **not** expected that
+//!   all types implement the [`Display`] trait.
+//! - [`fmt::Debug`][`Debug`] implementations should be implemented for **all** public types.
+//!   Output will typically represent the internal state as faithfully as possible.
+//!   The purpose of the [`Debug`] trait is to facilitate debugging Rust code. In
+//!   most cases, using `#[derive(Debug)]` is sufficient and recommended.
+//!
+//! Some examples of the output from both traits:
+//!
+//! ```
+//! assert_eq!(format!("{} {:?}", 3, 4), "3 4");
+//! assert_eq!(format!("{} {:?}", 'a', 'b'), "a 'b'");
+//! assert_eq!(format!("{} {:?}", "foo\n", "bar\n"), "foo\n \"bar\\n\"");
+//! ```
+//!
+//! # Related macros
+//!
+//! There are a number of related macros in the [`format!`] family. The ones that
+//! are currently implemented are:
+//!
+//! ```ignore (only-for-syntax-highlight)
+//! format!      // described above
+//! write!       // first argument is a &mut io::Write, the destination
+//! writeln!     // same as write but appends a newline
+//! print!       // the format string is printed to the standard output
+//! println!     // same as print but appends a newline
+//! eprint!      // the format string is printed to the standard error
+//! eprintln!    // same as eprint but appends a newline
+//! format_args! // described below.
+//! ```
+//!
+//! ### `write!`
+//!
+//! This and [`writeln!`] are two macros which are used to emit the format string
+//! to a specified stream. This is used to prevent intermediate allocations of
+//! format strings and instead directly write the output. Under the hood, this
+//! function is actually invoking the [`write_fmt`] function defined on the
+//! [`std::io::Write`] trait. Example usage is:
+//!
+//! ```
+//! # #![allow(unused_must_use)]
+//! use std::io::Write;
+//! let mut w = Vec::new();
+//! write!(&mut w, "Hello {}!", "world");
+//! ```
+//!
+//! ### `print!`
+//!
+//! This and [`println!`] emit their output to stdout. Similarly to the [`write!`]
+//! macro, the goal of these macros is to avoid intermediate allocations when
+//! printing output. Example usage is:
+//!
+//! ```
+//! print!("Hello {}!", "world");
+//! println!("I have a newline {}", "character at the end");
+//! ```
+//! ### `eprint!`
+//!
+//! The [`eprint!`] and [`eprintln!`] macros are identical to
+//! [`print!`] and [`println!`], respectively, except they emit their
+//! output to stderr.
+//!
+//! ### `format_args!`
+//!
+//! This is a curious macro used to safely pass around
+//! an opaque object describing the format string. This object
+//! does not require any heap allocations to create, and it only
+//! references information on the stack. Under the hood, all of
+//! the related macros are implemented in terms of this. First
+//! off, some example usage is:
+//!
+//! ```
+//! # #![allow(unused_must_use)]
+//! use std::fmt;
+//! use std::io::{self, Write};
+//!
+//! let mut some_writer = io::stdout();
+//! write!(&mut some_writer, "{}", format_args!("print with a {}", "macro"));
+//!
+//! fn my_fmt_fn(args: fmt::Arguments) {
+//!     write!(&mut io::stdout(), "{}", args);
+//! }
+//! my_fmt_fn(format_args!(", or a {} too", "function"));
+//! ```
+//!
+//! The result of the [`format_args!`] macro is a value of type [`fmt::Arguments`].
+//! This structure can then be passed to the [`write`] and [`format`] functions
+//! inside this module in order to process the format string.
+//! The goal of this macro is to even further prevent intermediate allocations
+//! when dealing with formatting strings.
+//!
+//! For example, a logging library could use the standard formatting syntax, but
+//! it would internally pass around this structure until it has been determined
+//! where output should go to.
+//!
+//! [`fmt::Result`]: Result
+//! [`Result`]: core::result::Result
+//! [`std::fmt::Error`]: Error
+//! [`write!`]: core::write
+//! [`write`]: core::write
+//! [`format!`]: crate::format
+//! [`to_string`]: crate::string::ToString
+//! [`writeln!`]: core::writeln
+//! [`write_fmt`]: ../../std/io/trait.Write.html#method.write_fmt
+//! [`std::io::Write`]: ../../std/io/trait.Write.html
+//! [`print!`]: ../../std/macro.print.html
+//! [`println!`]: ../../std/macro.println.html
+//! [`eprint!`]: ../../std/macro.eprint.html
+//! [`eprintln!`]: ../../std/macro.eprintln.html
+//! [`format_args!`]: core::format_args
+//! [`fmt::Arguments`]: Arguments
+//! [`format`]: crate::format
+
+#![stable(feature = "rust1", since = "1.0.0")]
+
+#[unstable(feature = "fmt_internals", issue = "none")]
+pub use core::fmt::rt;
+#[stable(feature = "fmt_flags_align", since = "1.28.0")]
+pub use core::fmt::Alignment;
+#[stable(feature = "rust1", since = "1.0.0")]
+pub use core::fmt::Error;
+#[stable(feature = "rust1", since = "1.0.0")]
+pub use core::fmt::{write, ArgumentV1, Arguments};
+#[stable(feature = "rust1", since = "1.0.0")]
+pub use core::fmt::{Binary, Octal};
+#[stable(feature = "rust1", since = "1.0.0")]
+pub use core::fmt::{Debug, Display};
+#[stable(feature = "rust1", since = "1.0.0")]
+pub use core::fmt::{DebugList, DebugMap, DebugSet, DebugStruct, DebugTuple};
+#[stable(feature = "rust1", since = "1.0.0")]
+pub use core::fmt::{Formatter, Result, Write};
+#[stable(feature = "rust1", since = "1.0.0")]
+pub use core::fmt::{LowerExp, UpperExp};
+#[stable(feature = "rust1", since = "1.0.0")]
+pub use core::fmt::{LowerHex, Pointer, UpperHex};
+
+use crate::string;
+
+/// The `format` function takes an [`Arguments`] struct and returns the resulting
+/// formatted string.
+///
+/// The [`Arguments`] instance can be created with the [`format_args!`] macro.
+///
+/// # Examples
+///
+/// Basic usage:
+///
+/// ```
+/// use std::fmt;
+///
+/// let s = fmt::format(format_args!("Hello, {}!", "world"));
+/// assert_eq!(s, "Hello, world!");
+/// ```
+///
+/// Please note that using [`format!`] might be preferable.
+/// Example:
+///
+/// ```
+/// let s = format!("Hello, {}!", "world");
+/// assert_eq!(s, "Hello, world!");
+/// ```
+///
+/// [`format_args!`]: core::format_args
+/// [`format!`]: crate::format
+#[stable(feature = "rust1", since = "1.0.0")]
+pub fn format(args: Arguments<'_>) -> string::String {
+    let capacity = args.estimated_capacity();
+    let mut output = string::String::with_capacity(capacity);
+    output.write_fmt(args).expect("a formatting trait implementation returned an error");
+    output
+}

library/alloc/src/lib.rs

@@ -0,0 +1,191 @@
+//! # The Rust core allocation and collections library
+//!
+//! This library provides smart pointers and collections for managing
+//! heap-allocated values.
+//!
+//! This library, like libcore, normally doesn’t need to be used directly
+//! since its contents are re-exported in the [`std` crate](../std/index.html).
+//! Crates that use the `#![no_std]` attribute however will typically
+//! not depend on `std`, so they’d use this crate instead.
+//!
+//! ## Boxed values
+//!
+//! The [`Box`] type is a smart pointer type. There can only be one owner of a
+//! [`Box`], and the owner can decide to mutate the contents, which live on the
+//! heap.
+//!
+//! This type can be sent among threads efficiently as the size of a `Box` value
+//! is the same as that of a pointer. Tree-like data structures are often built
+//! with boxes because each node often has only one owner, the parent.
+//!
+//! ## Reference counted pointers
+//!
+//! The [`Rc`] type is a non-threadsafe reference-counted pointer type intended
+//! for sharing memory within a thread. An [`Rc`] pointer wraps a type, `T`, and
+//! only allows access to `&T`, a shared reference.
+//!
+//! This type is useful when inherited mutability (such as using [`Box`]) is too
+//! constraining for an application, and is often paired with the [`Cell`] or
+//! [`RefCell`] types in order to allow mutation.
+//!
+//! ## Atomically reference counted pointers
+//!
+//! The [`Arc`] type is the threadsafe equivalent of the [`Rc`] type. It
+//! provides all the same functionality of [`Rc`], except it requires that the
+//! contained type `T` is shareable. Additionally, [`Arc<T>`][`Arc`] is itself
+//! sendable while [`Rc<T>`][`Rc`] is not.
+//!
+//! This type allows for shared access to the contained data, and is often
+//! paired with synchronization primitives such as mutexes to allow mutation of
+//! shared resources.
+//!
+//! ## Collections
+//!
+//! Implementations of the most common general purpose data structures are
+//! defined in this library. They are re-exported through the
+//! [standard collections library](../std/collections/index.html).
+//!
+//! ## Heap interfaces
+//!
+//! The [`alloc`](alloc/index.html) module defines the low-level interface to the
+//! default global allocator. It is not compatible with the libc allocator API.
+//!
+//! [`Arc`]: sync
+//! [`Box`]: boxed
+//! [`Cell`]: core::cell
+//! [`Rc`]: rc
+//! [`RefCell`]: core::cell
+
+#![allow(unused_attributes)]
+#![stable(feature = "alloc", since = "1.36.0")]
+#![doc(
+    html_root_url = "https://doc.rust-lang.org/nightly/",
+    html_playground_url = "https://play.rust-lang.org/",
+    issue_tracker_base_url = "https://github.com/rust-lang/rust/issues/",
+    test(no_crate_inject, attr(allow(unused_variables), deny(warnings)))
+)]
+#![no_std]
+#![needs_allocator]
+#![warn(deprecated_in_future)]
+#![warn(missing_docs)]
+#![warn(missing_debug_implementations)]
+#![allow(explicit_outlives_requirements)]
+#![allow(incomplete_features)]
+#![deny(unsafe_op_in_unsafe_fn)]
+#![cfg_attr(not(test), feature(generator_trait))]
+#![cfg_attr(test, feature(test))]
+#![feature(allocator_api)]
+#![feature(array_chunks)]
+#![feature(allow_internal_unstable)]
+#![feature(arbitrary_self_types)]
+#![feature(box_patterns)]
+#![feature(box_syntax)]
+#![feature(btree_drain_filter)]
+#![feature(cfg_sanitize)]
+#![feature(cfg_target_has_atomic)]
+#![feature(coerce_unsized)]
+#![feature(const_btree_new)]
+#![feature(const_generics)]
+#![feature(const_in_array_repeat_expressions)]
+#![feature(cow_is_borrowed)]
+#![feature(deque_range)]
+#![feature(dispatch_from_dyn)]
+#![feature(core_intrinsics)]
+#![feature(container_error_extra)]
+#![feature(dropck_eyepatch)]
+#![feature(exact_size_is_empty)]
+#![feature(exclusive_range_pattern)]
+#![feature(extend_one)]
+#![feature(fmt_internals)]
+#![feature(fn_traits)]
+#![feature(fundamental)]
+#![feature(internal_uninit_const)]
+#![feature(lang_items)]
+#![feature(layout_for_ptr)]
+#![feature(libc)]
+#![feature(map_first_last)]
+#![feature(map_into_keys_values)]
+#![feature(negative_impls)]
+#![feature(new_uninit)]
+#![feature(nll)]
+#![feature(nonnull_slice_from_raw_parts)]
+#![feature(optin_builtin_traits)]
+#![feature(or_patterns)]
+#![feature(pattern)]
+#![feature(ptr_internals)]
+#![feature(raw_ref_op)]
+#![feature(rustc_attrs)]
+#![feature(receiver_trait)]
+#![feature(min_specialization)]
+#![feature(slice_ptr_get)]
+#![feature(slice_ptr_len)]
+#![feature(staged_api)]
+#![feature(std_internals)]
+#![feature(str_internals)]
+#![feature(trusted_len)]
+#![feature(try_reserve)]
+#![feature(unboxed_closures)]
+#![feature(unicode_internals)]
+#![feature(unsafe_block_in_unsafe_fn)]
+#![feature(unsize)]
+#![feature(unsized_locals)]
+#![feature(allocator_internals)]
+#![feature(slice_partition_dedup)]
+#![feature(maybe_uninit_extra, maybe_uninit_slice)]
+#![feature(alloc_layout_extra)]
+#![feature(try_trait)]
+#![feature(associated_type_bounds)]
+// Allow testing this library
+
+#[cfg(test)]
+#[macro_use]
+extern crate std;
+#[cfg(test)]
+extern crate test;
+
+// Module with internal macros used by other modules (needs to be included before other modules).
+#[macro_use]
+mod macros;
+
+// Heaps provided for low-level allocation strategies
+
+pub mod alloc;
+
+// Primitive types using the heaps above
+
+// Need to conditionally define the mod from `boxed.rs` to avoid
+// duplicating the lang-items when building in test cfg; but also need
+// to allow code to have `use boxed::Box;` declarations.
+#[cfg(not(test))]
+pub mod boxed;
+#[cfg(test)]
+mod boxed {
+    pub use std::boxed::Box;
+}
+pub mod borrow;
+pub mod collections;
+pub mod fmt;
+pub mod prelude;
+pub mod raw_vec;
+pub mod rc;
+pub mod slice;
+pub mod str;
+pub mod string;
+#[cfg(target_has_atomic = "ptr")]
+pub mod sync;
+#[cfg(target_has_atomic = "ptr")]
+pub mod task;
+#[cfg(test)]
+mod tests;
+pub mod vec;
+
+#[cfg(not(test))]
+mod std {
+    pub use core::ops; // RangeFull
+}
+
+#[doc(hidden)]
+#[unstable(feature = "liballoc_internals", issue = "none", reason = "implementation detail")]
+pub mod __export {
+    pub use core::format_args;
+}

library/alloc/src/macros.rs

@@ -0,0 +1,109 @@
+/// Creates a [`Vec`] containing the arguments.
+///
+/// `vec!` allows `Vec`s to be defined with the same syntax as array expressions.
+/// There are two forms of this macro:
+///
+/// - Create a [`Vec`] containing a given list of elements:
+///
+/// ```
+/// let v = vec![1, 2, 3];
+/// assert_eq!(v[0], 1);
+/// assert_eq!(v[1], 2);
+/// assert_eq!(v[2], 3);
+/// ```
+///
+/// - Create a [`Vec`] from a given element and size:
+///
+/// ```
+/// let v = vec![1; 3];
+/// assert_eq!(v, [1, 1, 1]);
+/// ```
+///
+/// Note that unlike array expressions this syntax supports all elements
+/// which implement [`Clone`] and the number of elements doesn't have to be
+/// a constant.
+///
+/// This will use `clone` to duplicate an expression, so one should be careful
+/// using this with types having a nonstandard `Clone` implementation. For
+/// example, `vec![Rc::new(1); 5]` will create a vector of five references
+/// to the same boxed integer value, not five references pointing to independently
+/// boxed integers.
+///
+/// [`Vec`]: crate::vec::Vec
+#[cfg(not(test))]
+#[macro_export]
+#[stable(feature = "rust1", since = "1.0.0")]
+#[allow_internal_unstable(box_syntax)]
+macro_rules! vec {
+    () => (
+        $crate::vec::Vec::new()
+    );
+    ($elem:expr; $n:expr) => (
+        $crate::vec::from_elem($elem, $n)
+    );
+    ($($x:expr),+ $(,)?) => (
+        <[_]>::into_vec(box [$($x),+])
+    );
+}
+
+// HACK(japaric): with cfg(test) the inherent `[T]::into_vec` method, which is
+// required for this macro definition, is not available. Instead use the
+// `slice::into_vec`  function which is only available with cfg(test)
+// NB see the slice::hack module in slice.rs for more information
+#[cfg(test)]
+macro_rules! vec {
+    () => (
+        $crate::vec::Vec::new()
+    );
+    ($elem:expr; $n:expr) => (
+        $crate::vec::from_elem($elem, $n)
+    );
+    ($($x:expr),*) => (
+        $crate::slice::into_vec(box [$($x),*])
+    );
+    ($($x:expr,)*) => (vec![$($x),*])
+}
+
+/// Creates a `String` using interpolation of runtime expressions.
+///
+/// The first argument `format!` receives is a format string. This must be a string
+/// literal. The power of the formatting string is in the `{}`s contained.
+///
+/// Additional parameters passed to `format!` replace the `{}`s within the
+/// formatting string in the order given unless named or positional parameters
+/// are used; see [`std::fmt`][fmt] for more information.
+///
+/// A common use for `format!` is concatenation and interpolation of strings.
+/// The same convention is used with [`print!`] and [`write!`] macros,
+/// depending on the intended destination of the string.
+///
+/// To convert a single value to a string, use the [`to_string`] method. This
+/// will use the [`Display`] formatting trait.
+///
+/// [fmt]: core::fmt
+/// [`print!`]: ../std/macro.print.html
+/// [`write!`]: core::write
+/// [`to_string`]: crate::string::ToString
+/// [`Display`]: core::fmt::Display
+///
+/// # Panics
+///
+/// `format!` panics if a formatting trait implementation returns an error.
+/// This indicates an incorrect implementation
+/// since `fmt::Write for String` never returns an error itself.
+///
+/// # Examples
+///
+/// ```
+/// format!("test");
+/// format!("hello {}", "world!");
+/// format!("x = {}, y = {y}", 10, y = 30);
+/// ```
+#[macro_export]
+#[stable(feature = "rust1", since = "1.0.0")]
+macro_rules! format {
+    ($($arg:tt)*) => {{
+        let res = $crate::fmt::format($crate::__export::format_args!($($arg)*));
+        res
+    }}
+}

library/alloc/src/raw_vec.rs

@@ -1,25 +1,27 @@
 #![unstable(feature = "raw_vec_internals", reason = "implementation detail", issue = "none")]
 #![doc(hidden)]
 
-use core::alloc::{LayoutErr, MemoryBlock};
+use core::alloc::LayoutErr;
 use core::cmp;
 use core::mem::{self, ManuallyDrop, MaybeUninit};
 use core::ops::Drop;
 use core::ptr::{NonNull, Unique};
 use core::slice;
 
-use crate::alloc::{
+use crate::alloc::{handle_alloc_error, AllocRef, Global, Layout};
-    handle_alloc_error,
-    AllocInit::{self, *},
-    AllocRef, Global, Layout,
-    ReallocPlacement::{self, *},
-};
 use crate::boxed::Box;
 use crate::collections::TryReserveError::{self, *};
 
 #[cfg(test)]
 mod tests;
 
+enum AllocInit {
+    /// The contents of the new memory are uninitialized.
+    Uninitialized,
+    /// The new memory is guaranteed to be zeroed.
+    Zeroed,
+}
+
 /// A low-level utility for more ergonomically allocating, reallocating, and deallocating
 /// a buffer of memory on the heap without having to worry about all the corner cases
 /// involved. This type is excellent for building your own data structures like Vec and VecDeque.
@@ -156,14 +158,14 @@ impl<T, A: AllocRef> RawVec<T, A> {
     /// allocator for the returned `RawVec`.
     #[inline]
     pub fn with_capacity_in(capacity: usize, alloc: A) -> Self {
-        Self::allocate_in(capacity, Uninitialized, alloc)
+        Self::allocate_in(capacity, AllocInit::Uninitialized, alloc)
     }
 
     /// Like `with_capacity_zeroed`, but parameterized over the choice
     /// of allocator for the returned `RawVec`.
     #[inline]
     pub fn with_capacity_zeroed_in(capacity: usize, alloc: A) -> Self {
-        Self::allocate_in(capacity, Zeroed, alloc)
+        Self::allocate_in(capacity, AllocInit::Zeroed, alloc)
     }
 
     fn allocate_in(capacity: usize, init: AllocInit, mut alloc: A) -> Self {
@@ -180,14 +182,18 @@ impl<T, A: AllocRef> RawVec<T, A> {
                 Ok(_) => {}
                 Err(_) => capacity_overflow(),
             }
-            let memory = match alloc.alloc(layout, init) {
+            let result = match init {
-                Ok(memory) => memory,
+                AllocInit::Uninitialized => alloc.alloc(layout),
+                AllocInit::Zeroed => alloc.alloc_zeroed(layout),
+            };
+            let ptr = match result {
+                Ok(ptr) => ptr,
                 Err(_) => handle_alloc_error(layout),
             };
 
             Self {
-                ptr: unsafe { Unique::new_unchecked(memory.ptr.cast().as_ptr()) },
+                ptr: unsafe { Unique::new_unchecked(ptr.cast().as_ptr()) },
-                cap: Self::capacity_from_bytes(memory.size),
+                cap: Self::capacity_from_bytes(ptr.len()),
                 alloc,
             }
         }
@@ -197,13 +203,15 @@ impl<T, A: AllocRef> RawVec<T, A> {
     ///
     /// # Safety
     ///
-    /// The `ptr` must be allocated (via the given allocator `a`), and with the given `capacity`.
+    /// The `ptr` must be allocated (via the given allocator `alloc`), and with the given
+    /// `capacity`.
     /// The `capacity` cannot exceed `isize::MAX` for sized types. (only a concern on 32-bit
     /// systems). ZST vectors may have a capacity up to `usize::MAX`.
-    /// If the `ptr` and `capacity` come from a `RawVec` created via `a`, then this is guaranteed.
+    /// If the `ptr` and `capacity` come from a `RawVec` created via `alloc`, then this is
+    /// guaranteed.
     #[inline]
-    pub unsafe fn from_raw_parts_in(ptr: *mut T, capacity: usize, a: A) -> Self {
+    pub unsafe fn from_raw_parts_in(ptr: *mut T, capacity: usize, alloc: A) -> Self {
-        Self { ptr: unsafe { Unique::new_unchecked(ptr) }, cap: capacity, alloc: a }
+        Self { ptr: unsafe { Unique::new_unchecked(ptr) }, cap: capacity, alloc }
     }
 
     /// Gets a raw pointer to the start of the allocation. Note that this is
@@ -358,7 +366,7 @@ impl<T, A: AllocRef> RawVec<T, A> {
     ///
     /// Aborts on OOM.
     pub fn shrink_to_fit(&mut self, amount: usize) {
-        match self.shrink(amount, MayMove) {
+        match self.shrink(amount) {
             Err(CapacityOverflow) => capacity_overflow(),
             Err(AllocError { layout, .. }) => handle_alloc_error(layout),
             Ok(()) => { /* yay */ }
@@ -378,9 +386,9 @@ impl<T, A: AllocRef> RawVec<T, A> {
         excess / mem::size_of::<T>()
     }
 
-    fn set_memory(&mut self, memory: MemoryBlock) {
+    fn set_ptr(&mut self, ptr: NonNull<[u8]>) {
-        self.ptr = unsafe { Unique::new_unchecked(memory.ptr.cast().as_ptr()) };
+        self.ptr = unsafe { Unique::new_unchecked(ptr.cast().as_ptr()) };
-        self.cap = Self::capacity_from_bytes(memory.size);
+        self.cap = Self::capacity_from_bytes(ptr.len());
     }
 
     // This method is usually instantiated many times. So we want it to be as
@@ -426,8 +434,8 @@ impl<T, A: AllocRef> RawVec<T, A> {
         let new_layout = Layout::array::<T>(cap);
 
         // `finish_grow` is non-generic over `T`.
-        let memory = finish_grow(new_layout, self.current_memory(), &mut self.alloc)?;
+        let ptr = finish_grow(new_layout, self.current_memory(), &mut self.alloc)?;
-        self.set_memory(memory);
+        self.set_ptr(ptr);
         Ok(())
     }
 
@@ -445,30 +453,24 @@ impl<T, A: AllocRef> RawVec<T, A> {
         let new_layout = Layout::array::<T>(cap);
 
         // `finish_grow` is non-generic over `T`.
-        let memory = finish_grow(new_layout, self.current_memory(), &mut self.alloc)?;
+        let ptr = finish_grow(new_layout, self.current_memory(), &mut self.alloc)?;
-        self.set_memory(memory);
+        self.set_ptr(ptr);
         Ok(())
     }
 
-    fn shrink(
+    fn shrink(&mut self, amount: usize) -> Result<(), TryReserveError> {
-        &mut self,
-        amount: usize,
-        placement: ReallocPlacement,
-    ) -> Result<(), TryReserveError> {
         assert!(amount <= self.capacity(), "Tried to shrink to a larger capacity");
 
         let (ptr, layout) = if let Some(mem) = self.current_memory() { mem } else { return Ok(()) };
         let new_size = amount * mem::size_of::<T>();
 
-        let memory = unsafe {
+        let ptr = unsafe {
-            self.alloc.shrink(ptr, layout, new_size, placement).map_err(|_| {
+            self.alloc.shrink(ptr, layout, new_size).map_err(|_| TryReserveError::AllocError {
-                TryReserveError::AllocError {
                 layout: Layout::from_size_align_unchecked(new_size, layout.align()),
                 non_exhaustive: (),
-                }
             })?
         };
-        self.set_memory(memory);
+        self.set_ptr(ptr);
         Ok(())
     }
 }
@@ -481,7 +483,7 @@ fn finish_grow<A>(
     new_layout: Result<Layout, LayoutErr>,
     current_memory: Option<(NonNull<u8>, Layout)>,
     alloc: &mut A,
-) -> Result<MemoryBlock, TryReserveError>
+) -> Result<NonNull<[u8]>, TryReserveError>
 where
     A: AllocRef,
 {
@@ -492,9 +494,9 @@ where
 
     let memory = if let Some((ptr, old_layout)) = current_memory {
         debug_assert_eq!(old_layout.align(), new_layout.align());
-        unsafe { alloc.grow(ptr, old_layout, new_layout.size(), MayMove, Uninitialized) }
+        unsafe { alloc.grow(ptr, old_layout, new_layout.size()) }
     } else {
-        alloc.alloc(new_layout, Uninitialized)
+        alloc.alloc(new_layout)
     }
     .map_err(|_| AllocError { layout: new_layout, non_exhaustive: () })?;
 

library/alloc/src/raw_vec/tests.rs

@@ -0,0 +1,78 @@
+use super::*;
+
+#[test]
+fn allocator_param() {
+    use crate::alloc::AllocErr;
+
+    // Writing a test of integration between third-party
+    // allocators and `RawVec` is a little tricky because the `RawVec`
+    // API does not expose fallible allocation methods, so we
+    // cannot check what happens when allocator is exhausted
+    // (beyond detecting a panic).
+    //
+    // Instead, this just checks that the `RawVec` methods do at
+    // least go through the Allocator API when it reserves
+    // storage.
+
+    // A dumb allocator that consumes a fixed amount of fuel
+    // before allocation attempts start failing.
+    struct BoundedAlloc {
+        fuel: usize,
+    }
+    unsafe impl AllocRef for BoundedAlloc {
+        fn alloc(&mut self, layout: Layout) -> Result<NonNull<[u8]>, AllocErr> {
+            let size = layout.size();
+            if size > self.fuel {
+                return Err(AllocErr);
+            }
+            match Global.alloc(layout) {
+                ok @ Ok(_) => {
+                    self.fuel -= size;
+                    ok
+                }
+                err @ Err(_) => err,
+            }
+        }
+        unsafe fn dealloc(&mut self, ptr: NonNull<u8>, layout: Layout) {
+            unsafe { Global.dealloc(ptr, layout) }
+        }
+    }
+
+    let a = BoundedAlloc { fuel: 500 };
+    let mut v: RawVec<u8, _> = RawVec::with_capacity_in(50, a);
+    assert_eq!(v.alloc.fuel, 450);
+    v.reserve(50, 150); // (causes a realloc, thus using 50 + 150 = 200 units of fuel)
+    assert_eq!(v.alloc.fuel, 250);
+}
+
+#[test]
+fn reserve_does_not_overallocate() {
+    {
+        let mut v: RawVec<u32> = RawVec::new();
+        // First, `reserve` allocates like `reserve_exact`.
+        v.reserve(0, 9);
+        assert_eq!(9, v.capacity());
+    }
+
+    {
+        let mut v: RawVec<u32> = RawVec::new();
+        v.reserve(0, 7);
+        assert_eq!(7, v.capacity());
+        // 97 is more than double of 7, so `reserve` should work
+        // like `reserve_exact`.
+        v.reserve(7, 90);
+        assert_eq!(97, v.capacity());
+    }
+
+    {
+        let mut v: RawVec<u32> = RawVec::new();
+        v.reserve(0, 12);
+        assert_eq!(12, v.capacity());
+        v.reserve(12, 3);
+        // 3 is less than half of 12, so `reserve` must grow
+        // exponentially. At the time of writing this test grow
+        // factor is 2, so new capacity is 24, however, grow factor
+        // of 1.5 is OK too. Hence `>= 18` in assert.
+        assert!(v.capacity() >= 12 + 12 / 2);
+    }
+}

library/alloc/src/rc.rs

@@ -214,18 +214,15 @@
 //! }
 //! ```
 //!
-//! [`Rc`]: struct.Rc.html
+//! [clone]: Clone::clone
-//! [`Weak`]: struct.Weak.html
+//! [`Cell`]: core::cell::Cell
-//! [clone]: ../../std/clone/trait.Clone.html#tymethod.clone
+//! [`RefCell`]: core::cell::RefCell
-//! [`Cell`]: ../../std/cell/struct.Cell.html
+//! [send]: core::marker::Send
-//! [`RefCell`]: ../../std/cell/struct.RefCell.html
-//! [send]: ../../std/marker/trait.Send.html
 //! [arc]: ../../std/sync/struct.Arc.html
-//! [`Deref`]: ../../std/ops/trait.Deref.html
+//! [`Deref`]: core::ops::Deref
-//! [downgrade]: struct.Rc.html#method.downgrade
+//! [downgrade]: Rc::downgrade
-//! [upgrade]: struct.Weak.html#method.upgrade
+//! [upgrade]: Weak::upgrade
-//! [`None`]: ../../std/option/enum.Option.html#variant.None
+//! [mutability]: core::cell#introducing-mutability-inside-of-something-immutable
-//! [mutability]: ../../std/cell/index.html#introducing-mutability-inside-of-something-immutable
 
 #![stable(feature = "rust1", since = "1.0.0")]
 
@@ -235,7 +232,6 @@ use crate::boxed::Box;
 use std::boxed::Box;
 
 use core::any::Any;
-use core::array::LengthAtMost32;
 use core::borrow;
 use core::cell::Cell;
 use core::cmp::Ordering;
@@ -251,7 +247,7 @@ use core::pin::Pin;
 use core::ptr::{self, NonNull};
 use core::slice::from_raw_parts_mut;
 
-use crate::alloc::{box_free, handle_alloc_error, AllocInit, AllocRef, Global, Layout};
+use crate::alloc::{box_free, handle_alloc_error, AllocErr, AllocRef, Global, Layout};
 use crate::borrow::{Cow, ToOwned};
 use crate::string::String;
 use crate::vec::Vec;
@@ -353,9 +349,11 @@ impl<T> Rc<T> {
     #[unstable(feature = "new_uninit", issue = "63291")]
     pub fn new_uninit() -> Rc<mem::MaybeUninit<T>> {
         unsafe {
-            Rc::from_ptr(Rc::allocate_for_layout(Layout::new::<T>(), |mem| {
+            Rc::from_ptr(Rc::allocate_for_layout(
-                mem as *mut RcBox<mem::MaybeUninit<T>>
+                Layout::new::<T>(),
-            }))
+                |layout| Global.alloc(layout),
+                |mem| mem as *mut RcBox<mem::MaybeUninit<T>>,
+            ))
         }
     }
 
@@ -382,9 +380,11 @@ impl<T> Rc<T> {
     #[unstable(feature = "new_uninit", issue = "63291")]
     pub fn new_zeroed() -> Rc<mem::MaybeUninit<T>> {
         unsafe {
-            let mut uninit = Self::new_uninit();
+            Rc::from_ptr(Rc::allocate_for_layout(
-            ptr::write_bytes::<T>(Rc::get_mut_unchecked(&mut uninit).as_mut_ptr(), 0, 1);
+                Layout::new::<T>(),
-            uninit
+                |layout| Global.alloc_zeroed(layout),
+                |mem| mem as *mut RcBox<mem::MaybeUninit<T>>,
+            ))
         }
     }
 
@@ -397,13 +397,11 @@ impl<T> Rc<T> {
 
     /// Returns the inner value, if the `Rc` has exactly one strong reference.
     ///
-    /// Otherwise, an [`Err`][result] is returned with the same `Rc` that was
+    /// Otherwise, an [`Err`] is returned with the same `Rc` that was
     /// passed in.
     ///
     /// This will succeed even if there are outstanding weak references.
     ///
-    /// [result]: ../../std/result/enum.Result.html
-    ///
     /// # Examples
     ///
     /// ```
@@ -466,6 +464,40 @@ impl<T> Rc<[T]> {
     pub fn new_uninit_slice(len: usize) -> Rc<[mem::MaybeUninit<T>]> {
         unsafe { Rc::from_ptr(Rc::allocate_for_slice(len)) }
     }
+
+    /// Constructs a new reference-counted slice with uninitialized contents, with the memory being
+    /// filled with `0` bytes.
+    ///
+    /// See [`MaybeUninit::zeroed`][zeroed] for examples of correct and
+    /// incorrect usage of this method.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(new_uninit)]
+    ///
+    /// use std::rc::Rc;
+    ///
+    /// let values = Rc::<[u32]>::new_zeroed_slice(3);
+    /// let values = unsafe { values.assume_init() };
+    ///
+    /// assert_eq!(*values, [0, 0, 0])
+    /// ```
+    ///
+    /// [zeroed]: ../../std/mem/union.MaybeUninit.html#method.zeroed
+    #[unstable(feature = "new_uninit", issue = "63291")]
+    pub fn new_zeroed_slice(len: usize) -> Rc<[mem::MaybeUninit<T>]> {
+        unsafe {
+            Rc::from_ptr(Rc::allocate_for_layout(
+                Layout::array::<T>(len).unwrap(),
+                |layout| Global.alloc_zeroed(layout),
+                |mem| {
+                    ptr::slice_from_raw_parts_mut(mem as *mut T, len)
+                        as *mut RcBox<[mem::MaybeUninit<T>]>
+                },
+            ))
+        }
+    }
 }
 
 impl<T> Rc<mem::MaybeUninit<T>> {
@@ -554,7 +586,7 @@ impl<T: ?Sized> Rc<T> {
     /// To avoid a memory leak the pointer must be converted back to an `Rc` using
     /// [`Rc::from_raw`][from_raw].
     ///
-    /// [from_raw]: struct.Rc.html#method.from_raw
+    /// [from_raw]: Rc::from_raw
     ///
     /// # Examples
     ///
@@ -614,8 +646,8 @@ impl<T: ?Sized> Rc<T> {
     /// This function is unsafe because improper use may lead to memory unsafety,
     /// even if the returned `Rc<T>` is never accessed.
     ///
-    /// [into_raw]: struct.Rc.html#method.into_raw
+    /// [into_raw]: Rc::into_raw
-    /// [transmute]: ../../std/mem/fn.transmute.html
+    /// [transmute]: core::mem::transmute
     ///
     /// # Examples
     ///
@@ -646,32 +678,7 @@ impl<T: ?Sized> Rc<T> {
         unsafe { Self::from_ptr(rc_ptr) }
     }
 
-    /// Consumes the `Rc`, returning the wrapped pointer as `NonNull<T>`.
+    /// Creates a new [`Weak`] pointer to this allocation.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// #![feature(rc_into_raw_non_null)]
-    /// #![allow(deprecated)]
-    ///
-    /// use std::rc::Rc;
-    ///
-    /// let x = Rc::new("hello".to_owned());
-    /// let ptr = Rc::into_raw_non_null(x);
-    /// let deref = unsafe { ptr.as_ref() };
-    /// assert_eq!(deref, "hello");
-    /// ```
-    #[unstable(feature = "rc_into_raw_non_null", issue = "47336")]
-    #[rustc_deprecated(since = "1.44.0", reason = "use `Rc::into_raw` instead")]
-    #[inline]
-    pub fn into_raw_non_null(this: Self) -> NonNull<T> {
-        // safe because Rc guarantees its pointer is non-null
-        unsafe { NonNull::new_unchecked(Rc::into_raw(this) as *mut _) }
-    }
-
-    /// Creates a new [`Weak`][weak] pointer to this allocation.
-    ///
-    /// [weak]: struct.Weak.html
     ///
     /// # Examples
     ///
@@ -690,9 +697,7 @@ impl<T: ?Sized> Rc<T> {
         Weak { ptr: this.ptr }
     }
 
-    /// Gets the number of [`Weak`][weak] pointers to this allocation.
+    /// Gets the number of [`Weak`] pointers to this allocation.
-    ///
-    /// [weak]: struct.Weak.html
     ///
     /// # Examples
     ///
@@ -728,17 +733,15 @@ impl<T: ?Sized> Rc<T> {
         this.strong()
     }
 
-    /// Returns `true` if there are no other `Rc` or [`Weak`][weak] pointers to
+    /// Returns `true` if there are no other `Rc` or [`Weak`] pointers to
     /// this allocation.
-    ///
-    /// [weak]: struct.Weak.html
     #[inline]
     fn is_unique(this: &Self) -> bool {
         Rc::weak_count(this) == 0 && Rc::strong_count(this) == 1
     }
 
     /// Returns a mutable reference into the given `Rc`, if there are
-    /// no other `Rc` or [`Weak`][weak] pointers to the same allocation.
+    /// no other `Rc` or [`Weak`] pointers to the same allocation.
     ///
     /// Returns [`None`] otherwise, because it is not safe to
     /// mutate a shared value.
@@ -746,10 +749,8 @@ impl<T: ?Sized> Rc<T> {
     /// See also [`make_mut`][make_mut], which will [`clone`][clone]
     /// the inner value when there are other pointers.
     ///
-    /// [weak]: struct.Weak.html
+    /// [make_mut]: Rc::make_mut
-    /// [`None`]: ../../std/option/enum.Option.html#variant.None
+    /// [clone]: Clone::clone
-    /// [make_mut]: struct.Rc.html#method.make_mut
-    /// [clone]: ../../std/clone/trait.Clone.html#tymethod.clone
     ///
     /// # Examples
     ///
@@ -774,7 +775,7 @@ impl<T: ?Sized> Rc<T> {
     ///
     /// See also [`get_mut`], which is safe and does appropriate checks.
     ///
-    /// [`get_mut`]: struct.Rc.html#method.get_mut
+    /// [`get_mut`]: Rc::get_mut
     ///
     /// # Safety
     ///
@@ -820,7 +821,7 @@ impl<T: ?Sized> Rc<T> {
     /// assert!(!Rc::ptr_eq(&five, &other_five));
     /// ```
     ///
-    /// [`ptr::eq`]: ../../std/ptr/fn.eq.html
+    /// [`ptr::eq`]: core::ptr::eq
     pub fn ptr_eq(this: &Self, other: &Self) -> bool {
         this.ptr.as_ptr() == other.ptr.as_ptr()
     }
@@ -838,9 +839,8 @@ impl<T: Clone> Rc<T> {
     ///
     /// See also [`get_mut`], which will fail rather than cloning.
     ///
-    /// [`Weak`]: struct.Weak.html
+    /// [`clone`]: Clone::clone
-    /// [`clone`]: ../../std/clone/trait.Clone.html#tymethod.clone
+    /// [`get_mut`]: Rc::get_mut
-    /// [`get_mut`]: struct.Rc.html#method.get_mut
     ///
     /// # Examples
     ///
@@ -943,6 +943,7 @@ impl<T: ?Sized> Rc<T> {
     /// and must return back a (potentially fat)-pointer for the `RcBox<T>`.
     unsafe fn allocate_for_layout(
         value_layout: Layout,
+        allocate: impl FnOnce(Layout) -> Result<NonNull<[u8]>, AllocErr>,
         mem_to_rcbox: impl FnOnce(*mut u8) -> *mut RcBox<T>,
     ) -> *mut RcBox<T> {
         // Calculate layout using the given value layout.
@@ -952,12 +953,10 @@ impl<T: ?Sized> Rc<T> {
         let layout = Layout::new::<RcBox<()>>().extend(value_layout).unwrap().0.pad_to_align();
 
         // Allocate for the layout.
-        let mem = Global
+        let ptr = allocate(layout).unwrap_or_else(|_| handle_alloc_error(layout));
-            .alloc(layout, AllocInit::Uninitialized)
-            .unwrap_or_else(|_| handle_alloc_error(layout));
 
         // Initialize the RcBox
-        let inner = mem_to_rcbox(mem.ptr.as_ptr());
+        let inner = mem_to_rcbox(ptr.as_non_null_ptr().as_ptr());
         unsafe {
             debug_assert_eq!(Layout::for_value(&*inner), layout);
 
@@ -972,9 +971,11 @@ impl<T: ?Sized> Rc<T> {
     unsafe fn allocate_for_ptr(ptr: *const T) -> *mut RcBox<T> {
         // Allocate for the `RcBox<T>` using the given value.
         unsafe {
-            Self::allocate_for_layout(Layout::for_value(&*ptr), |mem| {
+            Self::allocate_for_layout(
-                set_data_ptr(ptr as *mut T, mem) as *mut RcBox<T>
+                Layout::for_value(&*ptr),
-            })
+                |layout| Global.alloc(layout),
+                |mem| set_data_ptr(ptr as *mut T, mem) as *mut RcBox<T>,
+            )
         }
     }
 
@@ -1005,9 +1006,11 @@ impl<T> Rc<[T]> {
     /// Allocates an `RcBox<[T]>` with the given length.
     unsafe fn allocate_for_slice(len: usize) -> *mut RcBox<[T]> {
         unsafe {
-            Self::allocate_for_layout(Layout::array::<T>(len).unwrap(), |mem| {
+            Self::allocate_for_layout(
-                ptr::slice_from_raw_parts_mut(mem as *mut T, len) as *mut RcBox<[T]>
+                Layout::array::<T>(len).unwrap(),
-            })
+                |layout| Global.alloc(layout),
+                |mem| ptr::slice_from_raw_parts_mut(mem as *mut T, len) as *mut RcBox<[T]>,
+            )
         }
     }
 }
@@ -1143,8 +1146,6 @@ unsafe impl<#[may_dangle] T: ?Sized> Drop for Rc<T> {
     /// drop(foo);    // Doesn't print anything
     /// drop(foo2);   // Prints "dropped!"
     /// ```
-    ///
-    /// [`Weak`]: ../../std/rc/struct.Weak.html
     fn drop(&mut self) {
         unsafe {
             self.dec_strong();
@@ -1516,10 +1517,7 @@ where
 }
 
 #[stable(feature = "boxed_slice_try_from", since = "1.43.0")]
-impl<T, const N: usize> TryFrom<Rc<[T]>> for Rc<[T; N]>
+impl<T, const N: usize> TryFrom<Rc<[T]>> for Rc<[T; N]> {
-where
-    [T; N]: LengthAtMost32,
-{
     type Error = Rc<[T]>;
 
     fn try_from(boxed_slice: Rc<[T]>) -> Result<Self, Self::Error> {
@@ -1629,11 +1627,7 @@ impl<T, I: iter::TrustedLen<Item = T>> ToRcSlice<T> for I {
 ///
 /// The typical way to obtain a `Weak` pointer is to call [`Rc::downgrade`].
 ///
-/// [`Rc`]: struct.Rc.html
+/// [`upgrade`]: Weak::upgrade
-/// [`Rc::downgrade`]: struct.Rc.html#method.downgrade
-/// [`upgrade`]: struct.Weak.html#method.upgrade
-/// [`Option`]: ../../std/option/enum.Option.html
-/// [`None`]: ../../std/option/enum.Option.html#variant.None
 #[stable(feature = "rc_weak", since = "1.4.0")]
 pub struct Weak<T: ?Sized> {
     // This is a `NonNull` to allow optimizing the size of this type in enums,
@@ -1660,8 +1654,7 @@ impl<T> Weak<T> {
     /// Constructs a new `Weak<T>`, without allocating any memory.
     /// Calling [`upgrade`] on the return value always gives [`None`].
     ///
-    /// [`upgrade`]: #method.upgrade
+    /// [`upgrade`]: Weak::upgrade
-    /// [`None`]: ../../std/option/enum.Option.html
     ///
     /// # Examples
     ///
@@ -1700,7 +1693,7 @@ impl<T> Weak<T> {
     /// // assert_eq!("hello", unsafe { &*weak.as_ptr() });
     /// ```
     ///
-    /// [`null`]: ../../std/ptr/fn.null.html
+    /// [`null`]: core::ptr::null
     #[stable(feature = "rc_as_ptr", since = "1.45.0")]
     pub fn as_ptr(&self) -> *const T {
         let ptr: *mut RcBox<T> = NonNull::as_ptr(self.ptr);
@@ -1719,8 +1712,9 @@ impl<T> Weak<T> {
 
     /// Consumes the `Weak<T>` and turns it into a raw pointer.
     ///
-    /// This converts the weak pointer into a raw pointer, preserving the original weak count. It
+    /// This converts the weak pointer into a raw pointer, while still preserving the ownership of
-    /// can be turned back into the `Weak<T>` with [`from_raw`].
+    /// one weak reference (the weak count is not modified by this operation). It can be turned
+    /// back into the `Weak<T>` with [`from_raw`].
     ///
     /// The same restrictions of accessing the target of the pointer as with
     /// [`as_ptr`] apply.
@@ -1741,8 +1735,8 @@ impl<T> Weak<T> {
     /// assert_eq!(0, Rc::weak_count(&strong));
     /// ```
     ///
-    /// [`from_raw`]: struct.Weak.html#method.from_raw
+    /// [`from_raw`]: Weak::from_raw
-    /// [`as_ptr`]: struct.Weak.html#method.as_ptr
+    /// [`as_ptr`]: Weak::as_ptr
     #[stable(feature = "weak_into_raw", since = "1.45.0")]
     pub fn into_raw(self) -> *const T {
         let result = self.as_ptr();
@@ -1755,17 +1749,18 @@ impl<T> Weak<T> {
     /// This can be used to safely get a strong reference (by calling [`upgrade`]
     /// later) or to deallocate the weak count by dropping the `Weak<T>`.
     ///
-    /// It takes ownership of one weak count (with the exception of pointers created by [`new`],
+    /// It takes ownership of one weak reference (with the exception of pointers created by [`new`],
-    /// as these don't have any corresponding weak count).
+    /// as these don't own anything; the method still works on them).
     ///
     /// # Safety
     ///
     /// The pointer must have originated from the [`into_raw`] and must still own its potential
-    /// weak reference count.
+    /// weak reference.
     ///
-    /// It is allowed for the strong count to be 0 at the time of calling this, but the weak count
+    /// It is allowed for the strong count to be 0 at the time of calling this. Nevertheless, this
-    /// must be non-zero or the pointer must have originated from a dangling `Weak<T>` (one created
+    /// takes ownership of one weak reference currently represented as a raw pointer (the weak
-    /// by [`new`]).
+    /// count is not modified by this operation) and therefore it must be paired with a previous
+    /// call to [`into_raw`].
     ///
     /// # Examples
     ///
@@ -1788,12 +1783,9 @@ impl<T> Weak<T> {
     /// assert!(unsafe { Weak::from_raw(raw_2) }.upgrade().is_none());
     /// ```
     ///
-    /// [`into_raw`]: struct.Weak.html#method.into_raw
+    /// [`into_raw`]: Weak::into_raw
-    /// [`upgrade`]: struct.Weak.html#method.upgrade
+    /// [`upgrade`]: Weak::upgrade
-    /// [`Rc`]: struct.Rc.html
+    /// [`new`]: Weak::new
-    /// [`Weak`]: struct.Weak.html
-    /// [`new`]: struct.Weak.html#method.new
-    /// [`forget`]: ../../std/mem/fn.forget.html
     #[stable(feature = "weak_into_raw", since = "1.45.0")]
     pub unsafe fn from_raw(ptr: *const T) -> Self {
         if ptr.is_null() {
@@ -1821,9 +1813,6 @@ impl<T: ?Sized> Weak<T> {
     ///
     /// Returns [`None`] if the inner value has since been dropped.
     ///
-    /// [`Rc`]: struct.Rc.html
-    /// [`None`]: ../../std/option/enum.Option.html
-    ///
     /// # Examples
     ///
     /// ```
@@ -1856,8 +1845,6 @@ impl<T: ?Sized> Weak<T> {
     /// Gets the number of strong (`Rc`) pointers pointing to this allocation.
     ///
     /// If `self` was created using [`Weak::new`], this will return 0.
-    ///
-    /// [`Weak::new`]: #method.new
     #[stable(feature = "weak_counts", since = "1.41.0")]
     pub fn strong_count(&self) -> usize {
         if let Some(inner) = self.inner() { inner.strong() } else { 0 }
@@ -1926,7 +1913,7 @@ impl<T: ?Sized> Weak<T> {
     /// assert!(!first.ptr_eq(&third));
     /// ```
     ///
-    /// [`ptr::eq`]: ../../std/ptr/fn.eq.html
+    /// [`ptr::eq`]: core::ptr::eq
     #[inline]
     #[stable(feature = "weak_ptr_eq", since = "1.39.0")]
     pub fn ptr_eq(&self, other: &Self) -> bool {
@@ -2008,8 +1995,8 @@ impl<T> Default for Weak<T> {
     /// Constructs a new `Weak<T>`, allocating memory for `T` without initializing
     /// it. Calling [`upgrade`] on the return value always gives [`None`].
     ///
-    /// [`None`]: ../../std/option/enum.Option.html
+    /// [`None`]: Option
-    /// [`upgrade`]: ../../std/rc/struct.Weak.html#method.upgrade
+    /// [`upgrade`]: Weak::upgrade
     ///
     /// # Examples
     ///
@@ -2117,7 +2104,7 @@ impl<T: ?Sized> AsRef<T> for Rc<T> {
 #[stable(feature = "pin", since = "1.33.0")]
 impl<T: ?Sized> Unpin for Rc<T> {}
 
-/// Get the offset within an `ArcInner` for
+/// Get the offset within an `RcBox` for
 /// a payload of type described by a pointer.
 ///
 /// # Safety
@@ -2126,7 +2113,7 @@ impl<T: ?Sized> Unpin for Rc<T> {}
 ///
 /// - This function is safe for any argument if `T` is sized, and
 /// - if `T` is unsized, the pointer must have appropriate pointer metadata
-///   aquired from the real instance that you are getting this offset for.
+///   acquired from the real instance that you are getting this offset for.
 unsafe fn data_offset<T: ?Sized>(ptr: *const T) -> isize {
     // Align the unsized value to the end of the `RcBox`.
     // Because it is ?Sized, it will always be the last field in memory.

library/alloc/src/str.rs

@@ -0,0 +1,576 @@
+//! Unicode string slices.
+//!
+//! *[See also the `str` primitive type](../../std/primitive.str.html).*
+//!
+//! The `&str` type is one of the two main string types, the other being `String`.
+//! Unlike its `String` counterpart, its contents are borrowed.
+//!
+//! # Basic Usage
+//!
+//! A basic string declaration of `&str` type:
+//!
+//! ```
+//! let hello_world = "Hello, World!";
+//! ```
+//!
+//! Here we have declared a string literal, also known as a string slice.
+//! String literals have a static lifetime, which means the string `hello_world`
+//! is guaranteed to be valid for the duration of the entire program.
+//! We can explicitly specify `hello_world`'s lifetime as well:
+//!
+//! ```
+//! let hello_world: &'static str = "Hello, world!";
+//! ```
+
+#![stable(feature = "rust1", since = "1.0.0")]
+// Many of the usings in this module are only used in the test configuration.
+// It's cleaner to just turn off the unused_imports warning than to fix them.
+#![allow(unused_imports)]
+
+use core::borrow::{Borrow, BorrowMut};
+use core::iter::FusedIterator;
+use core::mem;
+use core::ptr;
+use core::str::pattern::{DoubleEndedSearcher, Pattern, ReverseSearcher, Searcher};
+use core::unicode::conversions;
+
+use crate::borrow::ToOwned;
+use crate::boxed::Box;
+use crate::slice::{Concat, Join, SliceIndex};
+use crate::string::String;
+use crate::vec::Vec;
+
+#[stable(feature = "rust1", since = "1.0.0")]
+pub use core::str::pattern;
+#[stable(feature = "encode_utf16", since = "1.8.0")]
+pub use core::str::EncodeUtf16;
+#[stable(feature = "split_ascii_whitespace", since = "1.34.0")]
+pub use core::str::SplitAsciiWhitespace;
+#[stable(feature = "rust1", since = "1.0.0")]
+pub use core::str::SplitWhitespace;
+#[stable(feature = "rust1", since = "1.0.0")]
+pub use core::str::{from_utf8, from_utf8_mut, Bytes, CharIndices, Chars};
+#[stable(feature = "rust1", since = "1.0.0")]
+pub use core::str::{from_utf8_unchecked, from_utf8_unchecked_mut, ParseBoolError};
+#[stable(feature = "str_escape", since = "1.34.0")]
+pub use core::str::{EscapeDebug, EscapeDefault, EscapeUnicode};
+#[stable(feature = "rust1", since = "1.0.0")]
+pub use core::str::{FromStr, Utf8Error};
+#[allow(deprecated)]
+#[stable(feature = "rust1", since = "1.0.0")]
+pub use core::str::{Lines, LinesAny};
+#[stable(feature = "rust1", since = "1.0.0")]
+pub use core::str::{MatchIndices, RMatchIndices};
+#[stable(feature = "rust1", since = "1.0.0")]
+pub use core::str::{Matches, RMatches};
+#[stable(feature = "rust1", since = "1.0.0")]
+pub use core::str::{RSplit, Split};
+#[stable(feature = "rust1", since = "1.0.0")]
+pub use core::str::{RSplitN, SplitN};
+#[stable(feature = "rust1", since = "1.0.0")]
+pub use core::str::{RSplitTerminator, SplitTerminator};
+
+/// Note: `str` in `Concat<str>` is not meaningful here.
+/// This type parameter of the trait only exists to enable another impl.
+#[unstable(feature = "slice_concat_ext", issue = "27747")]
+impl<S: Borrow<str>> Concat<str> for [S] {
+    type Output = String;
+
+    fn concat(slice: &Self) -> String {
+        Join::join(slice, "")
+    }
+}
+
+#[unstable(feature = "slice_concat_ext", issue = "27747")]
+impl<S: Borrow<str>> Join<&str> for [S] {
+    type Output = String;
+
+    fn join(slice: &Self, sep: &str) -> String {
+        unsafe { String::from_utf8_unchecked(join_generic_copy(slice, sep.as_bytes())) }
+    }
+}
+
+macro_rules! spezialize_for_lengths {
+    ($separator:expr, $target:expr, $iter:expr; $($num:expr),*) => {
+        let mut target = $target;
+        let iter = $iter;
+        let sep_bytes = $separator;
+        match $separator.len() {
+            $(
+                // loops with hardcoded sizes run much faster
+                // specialize the cases with small separator lengths
+                $num => {
+                    for s in iter {
+                        copy_slice_and_advance!(target, sep_bytes);
+                        copy_slice_and_advance!(target, s.borrow().as_ref());
+                    }
+                },
+            )*
+            _ => {
+                // arbitrary non-zero size fallback
+                for s in iter {
+                    copy_slice_and_advance!(target, sep_bytes);
+                    copy_slice_and_advance!(target, s.borrow().as_ref());
+                }
+            }
+        }
+    };
+}
+
+macro_rules! copy_slice_and_advance {
+    ($target:expr, $bytes:expr) => {
+        let len = $bytes.len();
+        let (head, tail) = { $target }.split_at_mut(len);
+        head.copy_from_slice($bytes);
+        $target = tail;
+    };
+}
+
+// Optimized join implementation that works for both Vec<T> (T: Copy) and String's inner vec
+// Currently (2018-05-13) there is a bug with type inference and specialization (see issue #36262)
+// For this reason SliceConcat<T> is not specialized for T: Copy and SliceConcat<str> is the
+// only user of this function. It is left in place for the time when that is fixed.
+//
+// the bounds for String-join are S: Borrow<str> and for Vec-join Borrow<[T]>
+// [T] and str both impl AsRef<[T]> for some T
+// => s.borrow().as_ref() and we always have slices
+fn join_generic_copy<B, T, S>(slice: &[S], sep: &[T]) -> Vec<T>
+where
+    T: Copy,
+    B: AsRef<[T]> + ?Sized,
+    S: Borrow<B>,
+{
+    let sep_len = sep.len();
+    let mut iter = slice.iter();
+
+    // the first slice is the only one without a separator preceding it
+    let first = match iter.next() {
+        Some(first) => first,
+        None => return vec![],
+    };
+
+    // compute the exact total length of the joined Vec
+    // if the `len` calculation overflows, we'll panic
+    // we would have run out of memory anyway and the rest of the function requires
+    // the entire Vec pre-allocated for safety
+    let len = sep_len
+        .checked_mul(iter.len())
+        .and_then(|n| {
+            slice.iter().map(|s| s.borrow().as_ref().len()).try_fold(n, usize::checked_add)
+        })
+        .expect("attempt to join into collection with len > usize::MAX");
+
+    // crucial for safety
+    let mut result = Vec::with_capacity(len);
+    assert!(result.capacity() >= len);
+
+    result.extend_from_slice(first.borrow().as_ref());
+
+    unsafe {
+        {
+            let pos = result.len();
+            let target = result.get_unchecked_mut(pos..len);
+
+            // copy separator and slices over without bounds checks
+            // generate loops with hardcoded offsets for small separators
+            // massive improvements possible (~ x2)
+            spezialize_for_lengths!(sep, target, iter; 0, 1, 2, 3, 4);
+        }
+        result.set_len(len);
+    }
+    result
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl Borrow<str> for String {
+    #[inline]
+    fn borrow(&self) -> &str {
+        &self[..]
+    }
+}
+
+#[stable(feature = "string_borrow_mut", since = "1.36.0")]
+impl BorrowMut<str> for String {
+    #[inline]
+    fn borrow_mut(&mut self) -> &mut str {
+        &mut self[..]
+    }
+}
+
+#[stable(feature = "rust1", since = "1.0.0")]
+impl ToOwned for str {
+    type Owned = String;
+    #[inline]
+    fn to_owned(&self) -> String {
+        unsafe { String::from_utf8_unchecked(self.as_bytes().to_owned()) }
+    }
+
+    fn clone_into(&self, target: &mut String) {
+        let mut b = mem::take(target).into_bytes();
+        self.as_bytes().clone_into(&mut b);
+        *target = unsafe { String::from_utf8_unchecked(b) }
+    }
+}
+
+/// Methods for string slices.
+#[lang = "str_alloc"]
+#[cfg(not(test))]
+impl str {
+    /// Converts a `Box<str>` into a `Box<[u8]>` without copying or allocating.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// let s = "this is a string";
+    /// let boxed_str = s.to_owned().into_boxed_str();
+    /// let boxed_bytes = boxed_str.into_boxed_bytes();
+    /// assert_eq!(*boxed_bytes, *s.as_bytes());
+    /// ```
+    #[stable(feature = "str_box_extras", since = "1.20.0")]
+    #[inline]
+    pub fn into_boxed_bytes(self: Box<str>) -> Box<[u8]> {
+        self.into()
+    }
+
+    /// Replaces all matches of a pattern with another string.
+    ///
+    /// `replace` creates a new [`String`], and copies the data from this string slice into it.
+    /// While doing so, it attempts to find matches of a pattern. If it finds any, it
+    /// replaces them with the replacement string slice.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// let s = "this is old";
+    ///
+    /// assert_eq!("this is new", s.replace("old", "new"));
+    /// ```
+    ///
+    /// When the pattern doesn't match:
+    ///
+    /// ```
+    /// let s = "this is old";
+    /// assert_eq!(s, s.replace("cookie monster", "little lamb"));
+    /// ```
+    #[must_use = "this returns the replaced string as a new allocation, \
+                  without modifying the original"]
+    #[stable(feature = "rust1", since = "1.0.0")]
+    #[inline]
+    pub fn replace<'a, P: Pattern<'a>>(&'a self, from: P, to: &str) -> String {
+        let mut result = String::new();
+        let mut last_end = 0;
+        for (start, part) in self.match_indices(from) {
+            result.push_str(unsafe { self.get_unchecked(last_end..start) });
+            result.push_str(to);
+            last_end = start + part.len();
+        }
+        result.push_str(unsafe { self.get_unchecked(last_end..self.len()) });
+        result
+    }
+
+    /// Replaces first N matches of a pattern with another string.
+    ///
+    /// `replacen` creates a new [`String`], and copies the data from this string slice into it.
+    /// While doing so, it attempts to find matches of a pattern. If it finds any, it
+    /// replaces them with the replacement string slice at most `count` times.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// let s = "foo foo 123 foo";
+    /// assert_eq!("new new 123 foo", s.replacen("foo", "new", 2));
+    /// assert_eq!("faa fao 123 foo", s.replacen('o', "a", 3));
+    /// assert_eq!("foo foo new23 foo", s.replacen(char::is_numeric, "new", 1));
+    /// ```
+    ///
+    /// When the pattern doesn't match:
+    ///
+    /// ```
+    /// let s = "this is old";
+    /// assert_eq!(s, s.replacen("cookie monster", "little lamb", 10));
+    /// ```
+    #[must_use = "this returns the replaced string as a new allocation, \
+                  without modifying the original"]
+    #[stable(feature = "str_replacen", since = "1.16.0")]
+    pub fn replacen<'a, P: Pattern<'a>>(&'a self, pat: P, to: &str, count: usize) -> String {
+        // Hope to reduce the times of re-allocation
+        let mut result = String::with_capacity(32);
+        let mut last_end = 0;
+        for (start, part) in self.match_indices(pat).take(count) {
+            result.push_str(unsafe { self.get_unchecked(last_end..start) });
+            result.push_str(to);
+            last_end = start + part.len();
+        }
+        result.push_str(unsafe { self.get_unchecked(last_end..self.len()) });
+        result
+    }
+
+    /// Returns the lowercase equivalent of this string slice, as a new [`String`].
+    ///
+    /// 'Lowercase' is defined according to the terms of the Unicode Derived Core Property
+    /// `Lowercase`.
+    ///
+    /// Since some characters can expand into multiple characters when changing
+    /// the case, this function returns a [`String`] instead of modifying the
+    /// parameter in-place.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// let s = "HELLO";
+    ///
+    /// assert_eq!("hello", s.to_lowercase());
+    /// ```
+    ///
+    /// A tricky example, with sigma:
+    ///
+    /// ```
+    /// let sigma = "Σ";
+    ///
+    /// assert_eq!("σ", sigma.to_lowercase());
+    ///
+    /// // but at the end of a word, it's ς, not σ:
+    /// let odysseus = "ὈΔΥΣΣΕΎΣ";
+    ///
+    /// assert_eq!("ὀδυσσεύς", odysseus.to_lowercase());
+    /// ```
+    ///
+    /// Languages without case are not changed:
+    ///
+    /// ```
+    /// let new_year = "农历新年";
+    ///
+    /// assert_eq!(new_year, new_year.to_lowercase());
+    /// ```
+    #[stable(feature = "unicode_case_mapping", since = "1.2.0")]
+    pub fn to_lowercase(&self) -> String {
+        let mut s = String::with_capacity(self.len());
+        for (i, c) in self[..].char_indices() {
+            if c == 'Σ' {
+                // Σ maps to σ, except at the end of a word where it maps to ς.
+                // This is the only conditional (contextual) but language-independent mapping
+                // in `SpecialCasing.txt`,
+                // so hard-code it rather than have a generic "condition" mechanism.
+                // See https://github.com/rust-lang/rust/issues/26035
+                map_uppercase_sigma(self, i, &mut s)
+            } else {
+                match conversions::to_lower(c) {
+                    [a, '\0', _] => s.push(a),
+                    [a, b, '\0'] => {
+                        s.push(a);
+                        s.push(b);
+                    }
+                    [a, b, c] => {
+                        s.push(a);
+                        s.push(b);
+                        s.push(c);
+                    }
+                }
+            }
+        }
+        return s;
+
+        fn map_uppercase_sigma(from: &str, i: usize, to: &mut String) {
+            // See http://www.unicode.org/versions/Unicode7.0.0/ch03.pdf#G33992
+            // for the definition of `Final_Sigma`.
+            debug_assert!('Σ'.len_utf8() == 2);
+            let is_word_final = case_ignoreable_then_cased(from[..i].chars().rev())
+                && !case_ignoreable_then_cased(from[i + 2..].chars());
+            to.push_str(if is_word_final { "ς" } else { "σ" });
+        }
+
+        fn case_ignoreable_then_cased<I: Iterator<Item = char>>(iter: I) -> bool {
+            use core::unicode::derived_property::{Case_Ignorable, Cased};
+            match iter.skip_while(|&c| Case_Ignorable(c)).next() {
+                Some(c) => Cased(c),
+                None => false,
+            }
+        }
+    }
+
+    /// Returns the uppercase equivalent of this string slice, as a new [`String`].
+    ///
+    /// 'Uppercase' is defined according to the terms of the Unicode Derived Core Property
+    /// `Uppercase`.
+    ///
+    /// Since some characters can expand into multiple characters when changing
+    /// the case, this function returns a [`String`] instead of modifying the
+    /// parameter in-place.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// let s = "hello";
+    ///
+    /// assert_eq!("HELLO", s.to_uppercase());
+    /// ```
+    ///
+    /// Scripts without case are not changed:
+    ///
+    /// ```
+    /// let new_year = "农历新年";
+    ///
+    /// assert_eq!(new_year, new_year.to_uppercase());
+    /// ```
+    ///
+    /// One character can become multiple:
+    /// ```
+    /// let s = "tschüß";
+    ///
+    /// assert_eq!("TSCHÜSS", s.to_uppercase());
+    /// ```
+    #[stable(feature = "unicode_case_mapping", since = "1.2.0")]
+    pub fn to_uppercase(&self) -> String {
+        let mut s = String::with_capacity(self.len());
+        for c in self[..].chars() {
+            match conversions::to_upper(c) {
+                [a, '\0', _] => s.push(a),
+                [a, b, '\0'] => {
+                    s.push(a);
+                    s.push(b);
+                }
+                [a, b, c] => {
+                    s.push(a);
+                    s.push(b);
+                    s.push(c);
+                }
+            }
+        }
+        s
+    }
+
+    /// Converts a [`Box<str>`] into a [`String`] without copying or allocating.
+    ///
+    /// [`Box<str>`]: Box
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// let string = String::from("birthday gift");
+    /// let boxed_str = string.clone().into_boxed_str();
+    ///
+    /// assert_eq!(boxed_str.into_string(), string);
+    /// ```
+    #[stable(feature = "box_str", since = "1.4.0")]
+    #[inline]
+    pub fn into_string(self: Box<str>) -> String {
+        let slice = Box::<[u8]>::from(self);
+        unsafe { String::from_utf8_unchecked(slice.into_vec()) }
+    }
+
+    /// Creates a new [`String`] by repeating a string `n` times.
+    ///
+    /// # Panics
+    ///
+    /// This function will panic if the capacity would overflow.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// assert_eq!("abc".repeat(4), String::from("abcabcabcabc"));
+    /// ```
+    ///
+    /// A panic upon overflow:
+    ///
+    /// ```should_panic
+    /// // this will panic at runtime
+    /// "0123456789abcdef".repeat(usize::MAX);
+    /// ```
+    #[stable(feature = "repeat_str", since = "1.16.0")]
+    pub fn repeat(&self, n: usize) -> String {
+        unsafe { String::from_utf8_unchecked(self.as_bytes().repeat(n)) }
+    }
+
+    /// Returns a copy of this string where each character is mapped to its
+    /// ASCII upper case equivalent.
+    ///
+    /// ASCII letters 'a' to 'z' are mapped to 'A' to 'Z',
+    /// but non-ASCII letters are unchanged.
+    ///
+    /// To uppercase the value in-place, use [`make_ascii_uppercase`].
+    ///
+    /// To uppercase ASCII characters in addition to non-ASCII characters, use
+    /// [`to_uppercase`].
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let s = "Grüße, Jürgen ❤";
+    ///
+    /// assert_eq!("GRüßE, JüRGEN ❤", s.to_ascii_uppercase());
+    /// ```
+    ///
+    /// [`make_ascii_uppercase`]: str::make_ascii_uppercase
+    /// [`to_uppercase`]: #method.to_uppercase
+    #[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
+    #[inline]
+    pub fn to_ascii_uppercase(&self) -> String {
+        let mut bytes = self.as_bytes().to_vec();
+        bytes.make_ascii_uppercase();
+        // make_ascii_uppercase() preserves the UTF-8 invariant.
+        unsafe { String::from_utf8_unchecked(bytes) }
+    }
+
+    /// Returns a copy of this string where each character is mapped to its
+    /// ASCII lower case equivalent.
+    ///
+    /// ASCII letters 'A' to 'Z' are mapped to 'a' to 'z',
+    /// but non-ASCII letters are unchanged.
+    ///
+    /// To lowercase the value in-place, use [`make_ascii_lowercase`].
+    ///
+    /// To lowercase ASCII characters in addition to non-ASCII characters, use
+    /// [`to_lowercase`].
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let s = "Grüße, Jürgen ❤";
+    ///
+    /// assert_eq!("grüße, jürgen ❤", s.to_ascii_lowercase());
+    /// ```
+    ///
+    /// [`make_ascii_lowercase`]: str::make_ascii_lowercase
+    /// [`to_lowercase`]: #method.to_lowercase
+    #[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
+    #[inline]
+    pub fn to_ascii_lowercase(&self) -> String {
+        let mut bytes = self.as_bytes().to_vec();
+        bytes.make_ascii_lowercase();
+        // make_ascii_lowercase() preserves the UTF-8 invariant.
+        unsafe { String::from_utf8_unchecked(bytes) }
+    }
+}
+
+/// Converts a boxed slice of bytes to a boxed string slice without checking
+/// that the string contains valid UTF-8.
+///
+/// # Examples
+///
+/// Basic usage:
+///
+/// ```
+/// let smile_utf8 = Box::new([226, 152, 186]);
+/// let smile = unsafe { std::str::from_boxed_utf8_unchecked(smile_utf8) };
+///
+/// assert_eq!("☺", &*smile);
+/// ```
+#[stable(feature = "str_box_extras", since = "1.20.0")]
+#[inline]
+pub unsafe fn from_boxed_utf8_unchecked(v: Box<[u8]>) -> Box<str> {
+    unsafe { Box::from_raw(Box::into_raw(v) as *mut str) }
+}

library/alloc/src/string.rs

@@ -4,8 +4,6 @@
 //! [`ToString`]s, and several error types that may result from working with
 //! [`String`]s.
 //!
-//! [`ToString`]: trait.ToString.html
-//!
 //! # Examples
 //!
 //! There are multiple ways to create a new [`String`] from a string literal:
@@ -20,8 +18,6 @@
 //! You can create a new [`String`] from an existing one by concatenating with
 //! `+`:
 //!
-//! [`String`]: struct.String.html
-//!
 //! ```
 //! let s = "Hello".to_string();
 //!
@@ -67,11 +63,11 @@ use crate::vec::Vec;
 /// contents of the string. It has a close relationship with its borrowed
 /// counterpart, the primitive [`str`].
 ///
-/// [`str`]: ../../std/primitive.str.html
-///
 /// # Examples
 ///
-/// You can create a `String` from a literal string with [`String::from`]:
+/// You can create a `String` from [a literal string][`str`] with [`String::from`]:
+///
+/// [`String::from`]: From::from
 ///
 /// ```
 /// let hello = String::from("Hello, world!");
@@ -87,10 +83,8 @@ use crate::vec::Vec;
 /// hello.push_str("orld!");
 /// ```
 ///
-/// [`String::from`]: #method.from
+/// [`push`]: String::push
-/// [`char`]: ../../std/primitive.char.html
+/// [`push_str`]: String::push_str
-/// [`push`]: #method.push
-/// [`push_str`]: #method.push_str
 ///
 /// If you have a vector of UTF-8 bytes, you can create a `String` from it with
 /// the [`from_utf8`] method:
@@ -105,7 +99,7 @@ use crate::vec::Vec;
 /// assert_eq!("💖", sparkle_heart);
 /// ```
 ///
-/// [`from_utf8`]: #method.from_utf8
+/// [`from_utf8`]: String::from_utf8
 ///
 /// # UTF-8
 ///
@@ -128,8 +122,8 @@ use crate::vec::Vec;
 /// The [`bytes`] and [`chars`] methods return iterators over the first
 /// two, respectively.
 ///
-/// [`bytes`]: #method.bytes
+/// [`bytes`]: str::bytes
-/// [`chars`]: #method.chars
+/// [`chars`]: str::chars
 ///
 /// # Deref
 ///
@@ -215,9 +209,9 @@ use crate::vec::Vec;
 /// assert_eq!(String::from("Once upon a time..."), s);
 /// ```
 ///
-/// [`as_ptr`]: #method.as_ptr
+/// [`as_ptr`]: str::as_ptr
-/// [`len`]: #method.len
+/// [`len`]: String::len
-/// [`capacity`]: #method.capacity
+/// [`capacity`]: String::capacity
 ///
 /// If a `String` has enough capacity, adding elements to it will not
 /// re-allocate. For example, consider this program:
@@ -259,7 +253,7 @@ use crate::vec::Vec;
 /// }
 /// ```
 ///
-/// [`with_capacity`]: #method.with_capacity
+/// [`with_capacity`]: String::with_capacity
 ///
 /// We end up with a different output:
 ///
@@ -274,9 +268,10 @@ use crate::vec::Vec;
 ///
 /// Here, there's no need to allocate more memory inside the loop.
 ///
-/// [`&str`]: ../../std/primitive.str.html
+/// [`str`]: prim@str
-/// [`Deref`]: ../../std/ops/trait.Deref.html
+/// [`&str`]: prim@str
-/// [`as_str()`]: struct.String.html#method.as_str
+/// [`Deref`]: core::ops::Deref
+/// [`as_str()`]: String::as_str
 #[derive(PartialOrd, Eq, Ord)]
 #[cfg_attr(not(test), rustc_diagnostic_item = "string_type")]
 #[stable(feature = "rust1", since = "1.0.0")]
@@ -291,20 +286,18 @@ pub struct String {
 /// [`into_bytes`] method will give back the byte vector that was used in the
 /// conversion attempt.
 ///
-/// [`from_utf8`]: struct.String.html#method.from_utf8
+/// [`from_utf8`]: String::from_utf8
-/// [`String`]: struct.String.html
+/// [`into_bytes`]: FromUtf8Error::into_bytes
-/// [`into_bytes`]: struct.FromUtf8Error.html#method.into_bytes
 ///
 /// The [`Utf8Error`] type provided by [`std::str`] represents an error that may
 /// occur when converting a slice of [`u8`]s to a [`&str`]. In this sense, it's
 /// an analogue to `FromUtf8Error`, and you can get one from a `FromUtf8Error`
 /// through the [`utf8_error`] method.
 ///
-/// [`Utf8Error`]: ../../std/str/struct.Utf8Error.html
+/// [`Utf8Error`]: core::str::Utf8Error
-/// [`std::str`]: ../../std/str/index.html
+/// [`std::str`]: core::str
-/// [`u8`]: ../../std/primitive.u8.html
+/// [`&str`]: prim@str
-/// [`&str`]: ../../std/primitive.str.html
+/// [`utf8_error`]: Self::utf8_error
-/// [`utf8_error`]: #method.utf8_error
 ///
 /// # Examples
 ///
@@ -330,9 +323,7 @@ pub struct FromUtf8Error {
 ///
 /// This type is the error type for the [`from_utf16`] method on [`String`].
 ///
-/// [`from_utf16`]: struct.String.html#method.from_utf16
+/// [`from_utf16`]: String::from_utf16
-/// [`String`]: struct.String.html
-///
 /// # Examples
 ///
 /// Basic usage:
@@ -358,7 +349,7 @@ impl String {
     /// consider the [`with_capacity`] method to prevent excessive
     /// re-allocation.
     ///
-    /// [`with_capacity`]: #method.with_capacity
+    /// [`with_capacity`]: String::with_capacity
     ///
     /// # Examples
     ///
@@ -383,12 +374,12 @@ impl String {
     /// appending a bunch of data to the `String`, reducing the number of
     /// reallocations it needs to do.
     ///
-    /// [`capacity`]: #method.capacity
+    /// [`capacity`]: String::capacity
     ///
     /// If the given capacity is `0`, no allocation will occur, and this method
     /// is identical to the [`new`] method.
     ///
-    /// [`new`]: #method.new
+    /// [`new`]: String::new
     ///
     /// # Examples
     ///
@@ -479,15 +470,10 @@ impl String {
     /// See the docs for [`FromUtf8Error`] for more details on what you can do
     /// with this error.
     ///
-    /// [`from_utf8_unchecked`]: struct.String.html#method.from_utf8_unchecked
+    /// [`from_utf8_unchecked`]: String::from_utf8_unchecked
-    /// [`String`]: struct.String.html
+    /// [`Vec<u8>`]: crate::vec::Vec
-    /// [`u8`]: ../../std/primitive.u8.html
+    /// [`&str`]: prim@str
-    /// [`Vec<u8>`]: ../../std/vec/struct.Vec.html
+    /// [`into_bytes`]: String::into_bytes
-    /// [`&str`]: ../../std/primitive.str.html
-    /// [`str::from_utf8`]: ../../std/str/fn.from_utf8.html
-    /// [`into_bytes`]: struct.String.html#method.into_bytes
-    /// [`FromUtf8Error`]: struct.FromUtf8Error.html
-    /// [`Err`]: ../../std/result/enum.Result.html#variant.Err
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn from_utf8(vec: Vec<u8>) -> Result<String, FromUtf8Error> {
@@ -506,16 +492,15 @@ impl String {
     /// `from_utf8_lossy()` will replace any invalid UTF-8 sequences with
     /// [`U+FFFD REPLACEMENT CHARACTER`][U+FFFD], which looks like this: <20>
     ///
-    /// [`u8`]: ../../std/primitive.u8.html
     /// [byteslice]: ../../std/primitive.slice.html
-    /// [U+FFFD]: ../char/constant.REPLACEMENT_CHARACTER.html
+    /// [U+FFFD]: core::char::REPLACEMENT_CHARACTER
     ///
     /// If you are sure that the byte slice is valid UTF-8, and you don't want
     /// to incur the overhead of the conversion, there is an unsafe version
     /// of this function, [`from_utf8_unchecked`], which has the same behavior
     /// but skips the checks.
     ///
-    /// [`from_utf8_unchecked`]: struct.String.html#method.from_utf8_unchecked
+    /// [`from_utf8_unchecked`]: String::from_utf8_unchecked
     ///
     /// This function returns a [`Cow<'a, str>`]. If our byte slice is invalid
     /// UTF-8, then we need to insert the replacement characters, which will
@@ -523,7 +508,7 @@ impl String {
     /// it's already valid UTF-8, we don't need a new allocation. This return
     /// type allows us to handle both cases.
     ///
-    /// [`Cow<'a, str>`]: ../../std/borrow/enum.Cow.html
+    /// [`Cow<'a, str>`]: crate::borrow::Cow
     ///
     /// # Examples
     ///
@@ -583,8 +568,6 @@ impl String {
     /// Decode a UTF-16 encoded vector `v` into a `String`, returning [`Err`]
     /// if `v` contains any invalid data.
     ///
-    /// [`Err`]: ../../std/result/enum.Result.html#variant.Err
-    ///
     /// # Examples
     ///
     /// Basic usage:
@@ -623,9 +606,9 @@ impl String {
     /// `from_utf16_lossy` returns a `String` since the UTF-16 to UTF-8
     /// conversion requires a memory allocation.
     ///
-    /// [`from_utf8_lossy`]: #method.from_utf8_lossy
+    /// [`from_utf8_lossy`]: String::from_utf8_lossy
-    /// [`Cow<'a, str>`]: ../borrow/enum.Cow.html
+    /// [`Cow<'a, str>`]: crate::borrow::Cow
-    /// [U+FFFD]: ../char/constant.REPLACEMENT_CHARACTER.html
+    /// [U+FFFD]: core::char::REPLACEMENT_CHARACTER
     ///
     /// # Examples
     ///
@@ -659,7 +642,7 @@ impl String {
     /// into a `String` with the [`from_raw_parts`] function, allowing
     /// the destructor to perform the cleanup.
     ///
-    /// [`from_raw_parts`]: #method.from_raw_parts
+    /// [`from_raw_parts`]: String::from_raw_parts
     ///
     /// # Examples
     ///
@@ -684,15 +667,16 @@ impl String {
     /// This is highly unsafe, due to the number of invariants that aren't
     /// checked:
     ///
-    /// * The memory at `ptr` needs to have been previously allocated by the
+    /// * The memory at `buf` needs to have been previously allocated by the
     ///   same allocator the standard library uses, with a required alignment of exactly 1.
     /// * `length` needs to be less than or equal to `capacity`.
     /// * `capacity` needs to be the correct value.
+    /// * The first `length` bytes at `buf` need to be valid UTF-8.
     ///
     /// Violating these may cause problems like corrupting the allocator's
     /// internal data structures.
     ///
-    /// The ownership of `ptr` is effectively transferred to the
+    /// The ownership of `buf` is effectively transferred to the
     /// `String` which may then deallocate, reallocate or change the
     /// contents of memory pointed to by the pointer at will. Ensure
     /// that nothing else uses the pointer after calling this
@@ -732,7 +716,7 @@ impl String {
     ///
     /// See the safe version, [`from_utf8`], for more details.
     ///
-    /// [`from_utf8`]: struct.String.html#method.from_utf8
+    /// [`from_utf8`]: String::from_utf8
     ///
     /// # Safety
     ///
@@ -867,8 +851,7 @@ impl String {
     ///
     /// Panics if the new capacity overflows [`usize`].
     ///
-    /// [`reserve_exact`]: struct.String.html#method.reserve_exact
+    /// [`reserve_exact`]: String::reserve_exact
-    /// [`usize`]: ../../std/primitive.usize.html
     ///
     /// # Examples
     ///
@@ -911,7 +894,7 @@ impl String {
     /// Consider using the [`reserve`] method unless you absolutely know
     /// better than the allocator.
     ///
-    /// [`reserve`]: #method.reserve
+    /// [`reserve`]: String::reserve
     ///
     /// # Panics
     ///
@@ -1076,8 +1059,6 @@ impl String {
 
     /// Appends the given [`char`] to the end of this `String`.
     ///
-    /// [`char`]: ../../std/primitive.char.html
-    ///
     /// # Examples
     ///
     /// Basic usage:
@@ -1104,7 +1085,7 @@ impl String {
     ///
     /// The inverse of this method is [`from_utf8`].
     ///
-    /// [`from_utf8`]: #method.from_utf8
+    /// [`from_utf8`]: String::from_utf8
     ///
     /// # Examples
     ///
@@ -1133,8 +1114,6 @@ impl String {
     ///
     /// Panics if `new_len` does not lie on a [`char`] boundary.
     ///
-    /// [`char`]: ../../std/primitive.char.html
-    ///
     /// # Examples
     ///
     /// Basic usage:
@@ -1159,8 +1138,6 @@ impl String {
     ///
     /// Returns [`None`] if this `String` is empty.
     ///
-    /// [`None`]: ../../std/option/enum.Option.html#variant.None
-    ///
     /// # Examples
     ///
     /// Basic usage:
@@ -1187,7 +1164,7 @@ impl String {
 
     /// Removes a [`char`] from this `String` at a byte position and returns it.
     ///
-    /// This is an `O(n)` operation, as it requires copying every element in the
+    /// This is an *O*(*n*) operation, as it requires copying every element in the
     /// buffer.
     ///
     /// # Panics
@@ -1195,8 +1172,6 @@ impl String {
     /// Panics if `idx` is larger than or equal to the `String`'s length,
     /// or if it does not lie on a [`char`] boundary.
     ///
-    /// [`char`]: ../../std/primitive.char.html
-    ///
     /// # Examples
     ///
     /// Basic usage:
@@ -1289,7 +1264,7 @@ impl String {
 
     /// Inserts a character into this `String` at a byte position.
     ///
-    /// This is an `O(n)` operation as it requires copying every element in the
+    /// This is an *O*(*n*) operation as it requires copying every element in the
     /// buffer.
     ///
     /// # Panics
@@ -1297,8 +1272,6 @@ impl String {
     /// Panics if `idx` is larger than the `String`'s length, or if it does not
     /// lie on a [`char`] boundary.
     ///
-    /// [`char`]: ../../std/primitive.char.html
-    ///
     /// # Examples
     ///
     /// Basic usage:
@@ -1338,7 +1311,7 @@ impl String {
 
     /// Inserts a string slice into this `String` at a byte position.
     ///
-    /// This is an `O(n)` operation as it requires copying every element in the
+    /// This is an *O*(*n*) operation as it requires copying every element in the
     /// buffer.
     ///
     /// # Panics
@@ -1346,8 +1319,6 @@ impl String {
     /// Panics if `idx` is larger than the `String`'s length, or if it does not
     /// lie on a [`char`] boundary.
     ///
-    /// [`char`]: ../../std/primitive.char.html
-    ///
     /// # Examples
     ///
     /// Basic usage:
@@ -1507,8 +1478,6 @@ impl String {
     /// Panics if the starting point or end point do not lie on a [`char`]
     /// boundary, or if they're out of bounds.
     ///
-    /// [`char`]: ../../std/primitive.char.html
-    ///
     /// # Examples
     ///
     /// Basic usage:
@@ -1567,9 +1536,6 @@ impl String {
     /// Panics if the starting point or end point do not lie on a [`char`]
     /// boundary, or if they're out of bounds.
     ///
-    /// [`char`]: ../../std/primitive.char.html
-    /// [`Vec::splice`]: ../../std/vec/struct.Vec.html#method.splice
-    ///
     /// # Examples
     ///
     /// Basic usage:
@@ -1610,8 +1576,7 @@ impl String {
     ///
     /// This will drop any excess capacity.
     ///
-    /// [`Box`]: ../../std/boxed/struct.Box.html
+    /// [`str`]: prim@str
-    /// [`str`]: ../../std/primitive.str.html
     ///
     /// # Examples
     ///
@@ -1680,10 +1645,8 @@ impl FromUtf8Error {
     /// an analogue to `FromUtf8Error`. See its documentation for more details
     /// on using it.
     ///
-    /// [`Utf8Error`]: ../../std/str/struct.Utf8Error.html
+    /// [`std::str`]: core::str
-    /// [`std::str`]: ../../std/str/index.html
+    /// [`&str`]: prim@str
-    /// [`u8`]: ../../std/primitive.u8.html
-    /// [`&str`]: ../../std/primitive.str.html
     ///
     /// # Examples
     ///
@@ -2012,7 +1975,7 @@ impl hash::Hash for String {
 ///
 /// This consumes the `String` on the left-hand side and re-uses its buffer (growing it if
 /// necessary). This is done to avoid allocating a new `String` and copying the entire contents on
-/// every operation, which would lead to `O(n^2)` running time when building an `n`-byte string by
+/// every operation, which would lead to *O*(*n*^2) running time when building an *n*-byte string by
 /// repeated concatenation.
 ///
 /// The string on the right-hand side is only borrowed; its contents are copied into the returned
@@ -2187,7 +2150,7 @@ impl ops::DerefMut for String {
 ///
 /// This alias exists for backwards compatibility, and may be eventually deprecated.
 ///
-/// [`Infallible`]: ../../core/convert/enum.Infallible.html
+/// [`Infallible`]: core::convert::Infallible
 #[stable(feature = "str_parse_error", since = "1.5.0")]
 pub type ParseError = core::convert::Infallible;
 
@@ -2207,7 +2170,7 @@ impl FromStr for String {
 /// [`Display`] should be implemented instead, and you get the `ToString`
 /// implementation for free.
 ///
-/// [`Display`]: ../../std/fmt/trait.Display.html
+/// [`Display`]: fmt::Display
 #[stable(feature = "rust1", since = "1.0.0")]
 pub trait ToString {
     /// Converts the given value to a `String`.
@@ -2235,6 +2198,9 @@ pub trait ToString {
 /// since `fmt::Write for String` never returns an error itself.
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: fmt::Display + ?Sized> ToString for T {
+    // A common guideline is to not inline generic functions. However,
+    // remove `#[inline]` from this method causes non-negligible regression.
+    // See <https://github.com/rust-lang/rust/pull/74852> as last attempt try to remove it.
     #[inline]
     default fn to_string(&self) -> String {
         use fmt::Write;
@@ -2465,8 +2431,7 @@ impl fmt::Write for String {
 /// This struct is created by the [`drain`] method on [`String`]. See its
 /// documentation for more.
 ///
-/// [`drain`]: struct.String.html#method.drain
+/// [`drain`]: String::drain
-/// [`String`]: struct.String.html
 #[stable(feature = "drain", since = "1.6.0")]
 pub struct Drain<'a> {
     /// Will be used as &'a mut String in the destructor

library/alloc/src/sync.rs

@@ -2,12 +2,9 @@
 
 //! Thread-safe reference-counting pointers.
 //!
-//! See the [`Arc<T>`][arc] documentation for more details.
+//! See the [`Arc<T>`][Arc] documentation for more details.
-//!
-//! [arc]: struct.Arc.html
 
 use core::any::Any;
-use core::array::LengthAtMost32;
 use core::borrow;
 use core::cmp::Ordering;
 use core::convert::{From, TryFrom};
@@ -24,7 +21,7 @@ use core::slice::from_raw_parts_mut;
 use core::sync::atomic;
 use core::sync::atomic::Ordering::{Acquire, Relaxed, Release, SeqCst};
 
-use crate::alloc::{box_free, handle_alloc_error, AllocInit, AllocRef, Global, Layout};
+use crate::alloc::{box_free, handle_alloc_error, AllocErr, AllocRef, Global, Layout};
 use crate::borrow::{Cow, ToOwned};
 use crate::boxed::Box;
 use crate::rc::is_dangling;
@@ -101,21 +98,21 @@ macro_rules! acquire {
 /// ## Breaking cycles with `Weak`
 ///
 /// The [`downgrade`][downgrade] method can be used to create a non-owning
-/// [`Weak`][weak] pointer. A [`Weak`][weak] pointer can be [`upgrade`][upgrade]d
+/// [`Weak`] pointer. A [`Weak`] pointer can be [`upgrade`][upgrade]d
 /// to an `Arc`, but this will return [`None`] if the value stored in the allocation has
 /// already been dropped. In other words, `Weak` pointers do not keep the value
 /// inside the allocation alive; however, they *do* keep the allocation
 /// (the backing store for the value) alive.
 ///
 /// A cycle between `Arc` pointers will never be deallocated. For this reason,
-/// [`Weak`][weak] is used to break cycles. For example, a tree could have
+/// [`Weak`] is used to break cycles. For example, a tree could have
-/// strong `Arc` pointers from parent nodes to children, and [`Weak`][weak]
+/// strong `Arc` pointers from parent nodes to children, and [`Weak`]
 /// pointers from children back to their parents.
 ///
 /// # Cloning references
 ///
 /// Creating a new reference from an existing reference counted pointer is done using the
-/// `Clone` trait implemented for [`Arc<T>`][arc] and [`Weak<T>`][weak].
+/// `Clone` trait implemented for [`Arc<T>`][Arc] and [`Weak<T>`][Weak].
 ///
 /// ```
 /// use std::sync::Arc;
@@ -140,23 +137,20 @@ macro_rules! acquire {
 /// Arc::downgrade(&my_arc);
 /// ```
 ///
-/// [`Weak<T>`][weak] does not auto-dereference to `T`, because the inner value may have
+/// [`Weak<T>`][Weak] does not auto-dereference to `T`, because the inner value may have
 /// already been dropped.
 ///
-/// [arc]: struct.Arc.html
+/// [`Rc<T>`]: crate::rc::Rc
-/// [weak]: struct.Weak.html
+/// [clone]: Clone::clone
-/// [`Rc<T>`]: ../../std/rc/struct.Rc.html
-/// [clone]: ../../std/clone/trait.Clone.html#tymethod.clone
 /// [mutex]: ../../std/sync/struct.Mutex.html
 /// [rwlock]: ../../std/sync/struct.RwLock.html
-/// [atomic]: ../../std/sync/atomic/index.html
+/// [atomic]: core::sync::atomic
-/// [`Send`]: ../../std/marker/trait.Send.html
+/// [`Send`]: core::marker::Send
-/// [`Sync`]: ../../std/marker/trait.Sync.html
+/// [`Sync`]: core::marker::Sync
-/// [deref]: ../../std/ops/trait.Deref.html
+/// [deref]: core::ops::Deref
-/// [downgrade]: struct.Arc.html#method.downgrade
+/// [downgrade]: Arc::downgrade
-/// [upgrade]: struct.Weak.html#method.upgrade
+/// [upgrade]: Weak::upgrade
-/// [`None`]: ../../std/option/enum.Option.html#variant.None
+/// [`RefCell<T>`]: core::cell::RefCell
-/// [`RefCell<T>`]: ../../std/cell/struct.RefCell.html
 /// [`std::sync`]: ../../std/sync/index.html
 /// [`Arc::clone(&from)`]: #method.clone
 ///
@@ -185,7 +179,7 @@ macro_rules! acquire {
 ///
 /// Sharing a mutable [`AtomicUsize`]:
 ///
-/// [`AtomicUsize`]: ../../std/sync/atomic/struct.AtomicUsize.html
+/// [`AtomicUsize`]: core::sync::atomic::AtomicUsize
 ///
 /// ```no_run
 /// use std::sync::Arc;
@@ -255,11 +249,7 @@ impl<T: ?Sized> Arc<T> {
 ///
 /// The typical way to obtain a `Weak` pointer is to call [`Arc::downgrade`].
 ///
-/// [`Arc`]: struct.Arc.html
+/// [`upgrade`]: Weak::upgrade
-/// [`Arc::downgrade`]: struct.Arc.html#method.downgrade
-/// [`upgrade`]: struct.Weak.html#method.upgrade
-/// [`Option`]: ../../std/option/enum.Option.html
-/// [`None`]: ../../std/option/enum.Option.html#variant.None
 #[stable(feature = "arc_weak", since = "1.4.0")]
 pub struct Weak<T: ?Sized> {
     // This is a `NonNull` to allow optimizing the size of this type in enums,
@@ -329,6 +319,79 @@ impl<T> Arc<T> {
         Self::from_inner(Box::leak(x).into())
     }
 
+    /// Constructs a new `Arc<T>` using a weak reference to itself. Attempting
+    /// to upgrade the weak reference before this function returns will result
+    /// in a `None` value. However, the weak reference may be cloned freely and
+    /// stored for use at a later time.
+    ///
+    /// # Examples
+    /// ```
+    /// #![feature(arc_new_cyclic)]
+    /// #![allow(dead_code)]
+    ///
+    /// use std::sync::{Arc, Weak};
+    ///
+    /// struct Foo {
+    ///     me: Weak<Foo>,
+    /// }
+    ///
+    /// let foo = Arc::new_cyclic(|me| Foo {
+    ///     me: me.clone(),
+    /// });
+    /// ```
+    #[inline]
+    #[unstable(feature = "arc_new_cyclic", issue = "75861")]
+    pub fn new_cyclic(data_fn: impl FnOnce(&Weak<T>) -> T) -> Arc<T> {
+        // Construct the inner in the "uninitialized" state with a single
+        // weak reference.
+        let uninit_ptr: NonNull<_> = Box::leak(box ArcInner {
+            strong: atomic::AtomicUsize::new(0),
+            weak: atomic::AtomicUsize::new(1),
+            data: mem::MaybeUninit::<T>::uninit(),
+        })
+        .into();
+        let init_ptr: NonNull<ArcInner<T>> = uninit_ptr.cast();
+
+        let weak = Weak { ptr: init_ptr };
+
+        // It's important we don't give up ownership of the weak pointer, or
+        // else the memory might be freed by the time `data_fn` returns. If
+        // we really wanted to pass ownership, we could create an additional
+        // weak pointer for ourselves, but this would result in additional
+        // updates to the weak reference count which might not be necessary
+        // otherwise.
+        let data = data_fn(&weak);
+
+        // Now we can properly initialize the inner value and turn our weak
+        // reference into a strong reference.
+        unsafe {
+            let inner = init_ptr.as_ptr();
+            ptr::write(&raw mut (*inner).data, data);
+
+            // The above write to the data field must be visible to any threads which
+            // observe a non-zero strong count. Therefore we need at least "Release" ordering
+            // in order to synchronize with the `compare_exchange_weak` in `Weak::upgrade`.
+            //
+            // "Acquire" ordering is not required. When considering the possible behaviours
+            // of `data_fn` we only need to look at what it could do with a reference to a
+            // non-upgradeable `Weak`:
+            // - It can *clone* the `Weak`, increasing the weak reference count.
+            // - It can drop those clones, decreasing the weak reference count (but never to zero).
+            //
+            // These side effects do not impact us in any way, and no other side effects are
+            // possible with safe code alone.
+            let prev_value = (*inner).strong.fetch_add(1, Release);
+            debug_assert_eq!(prev_value, 0, "No prior strong references should exist");
+        }
+
+        let strong = Arc::from_inner(init_ptr);
+
+        // Strong references should collectively own a shared weak reference,
+        // so don't run the destructor for our old weak reference.
+        mem::forget(weak);
+        strong
+    }
+
     /// Constructs a new `Arc` with uninitialized contents.
     ///
     /// # Examples
@@ -353,9 +416,11 @@ impl<T> Arc<T> {
     #[unstable(feature = "new_uninit", issue = "63291")]
     pub fn new_uninit() -> Arc<mem::MaybeUninit<T>> {
         unsafe {
-            Arc::from_ptr(Arc::allocate_for_layout(Layout::new::<T>(), |mem| {
+            Arc::from_ptr(Arc::allocate_for_layout(
-                mem as *mut ArcInner<mem::MaybeUninit<T>>
+                Layout::new::<T>(),
-            }))
+                |layout| Global.alloc(layout),
+                |mem| mem as *mut ArcInner<mem::MaybeUninit<T>>,
+            ))
         }
     }
 
@@ -382,9 +447,11 @@ impl<T> Arc<T> {
     #[unstable(feature = "new_uninit", issue = "63291")]
     pub fn new_zeroed() -> Arc<mem::MaybeUninit<T>> {
         unsafe {
-            let mut uninit = Self::new_uninit();
+            Arc::from_ptr(Arc::allocate_for_layout(
-            ptr::write_bytes::<T>(Arc::get_mut_unchecked(&mut uninit).as_mut_ptr(), 0, 1);
+                Layout::new::<T>(),
-            uninit
+                |layout| Global.alloc_zeroed(layout),
+                |mem| mem as *mut ArcInner<mem::MaybeUninit<T>>,
+            ))
         }
     }
 
@@ -397,13 +464,11 @@ impl<T> Arc<T> {
 
     /// Returns the inner value, if the `Arc` has exactly one strong reference.
     ///
-    /// Otherwise, an [`Err`][result] is returned with the same `Arc` that was
+    /// Otherwise, an [`Err`] is returned with the same `Arc` that was
     /// passed in.
     ///
     /// This will succeed even if there are outstanding weak references.
     ///
-    /// [result]: ../../std/result/enum.Result.html
-    ///
     /// # Examples
     ///
     /// ```
@@ -438,7 +503,7 @@ impl<T> Arc<T> {
 }
 
 impl<T> Arc<[T]> {
-    /// Constructs a new reference-counted slice with uninitialized contents.
+    /// Constructs a new atomically reference-counted slice with uninitialized contents.
     ///
     /// # Examples
     ///
@@ -465,6 +530,40 @@ impl<T> Arc<[T]> {
     pub fn new_uninit_slice(len: usize) -> Arc<[mem::MaybeUninit<T>]> {
         unsafe { Arc::from_ptr(Arc::allocate_for_slice(len)) }
     }
+
+    /// Constructs a new atomically reference-counted slice with uninitialized contents, with the memory being
+    /// filled with `0` bytes.
+    ///
+    /// See [`MaybeUninit::zeroed`][zeroed] for examples of correct and
+    /// incorrect usage of this method.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(new_uninit)]
+    ///
+    /// use std::sync::Arc;
+    ///
+    /// let values = Arc::<[u32]>::new_zeroed_slice(3);
+    /// let values = unsafe { values.assume_init() };
+    ///
+    /// assert_eq!(*values, [0, 0, 0])
+    /// ```
+    ///
+    /// [zeroed]: ../../std/mem/union.MaybeUninit.html#method.zeroed
+    #[unstable(feature = "new_uninit", issue = "63291")]
+    pub fn new_zeroed_slice(len: usize) -> Arc<[mem::MaybeUninit<T>]> {
+        unsafe {
+            Arc::from_ptr(Arc::allocate_for_layout(
+                Layout::array::<T>(len).unwrap(),
+                |layout| Global.alloc_zeroed(layout),
+                |mem| {
+                    ptr::slice_from_raw_parts_mut(mem as *mut T, len)
+                        as *mut ArcInner<[mem::MaybeUninit<T>]>
+                },
+            ))
+        }
+    }
 }
 
 impl<T> Arc<mem::MaybeUninit<T>> {
@@ -551,9 +650,7 @@ impl<T: ?Sized> Arc<T> {
     /// Consumes the `Arc`, returning the wrapped pointer.
     ///
     /// To avoid a memory leak the pointer must be converted back to an `Arc` using
-    /// [`Arc::from_raw`][from_raw].
+    /// [`Arc::from_raw`].
-    ///
-    /// [from_raw]: struct.Arc.html#method.from_raw
     ///
     /// # Examples
     ///
@@ -573,7 +670,7 @@ impl<T: ?Sized> Arc<T> {
 
     /// Provides a raw pointer to the data.
     ///
-    /// The counts are not affected in way and the `Arc` is not consumed. The pointer is valid for
+    /// The counts are not affected in any way and the `Arc` is not consumed. The pointer is valid for
     /// as long as there are strong counts in the `Arc`.
     ///
     /// # Examples
@@ -613,8 +710,8 @@ impl<T: ?Sized> Arc<T> {
     /// This function is unsafe because improper use may lead to memory unsafety,
     /// even if the returned `Arc<T>` is never accessed.
     ///
-    /// [into_raw]: struct.Arc.html#method.into_raw
+    /// [into_raw]: Arc::into_raw
-    /// [transmute]: ../../std/mem/fn.transmute.html
+    /// [transmute]: core::mem::transmute
     ///
     /// # Examples
     ///
@@ -647,32 +744,7 @@ impl<T: ?Sized> Arc<T> {
         }
     }
 
-    /// Consumes the `Arc`, returning the wrapped pointer as `NonNull<T>`.
+    /// Creates a new [`Weak`] pointer to this allocation.
-    ///
-    /// # Examples
-    ///
-    /// ```
-    /// #![feature(rc_into_raw_non_null)]
-    /// #![allow(deprecated)]
-    ///
-    /// use std::sync::Arc;
-    ///
-    /// let x = Arc::new("hello".to_owned());
-    /// let ptr = Arc::into_raw_non_null(x);
-    /// let deref = unsafe { ptr.as_ref() };
-    /// assert_eq!(deref, "hello");
-    /// ```
-    #[unstable(feature = "rc_into_raw_non_null", issue = "47336")]
-    #[rustc_deprecated(since = "1.44.0", reason = "use `Arc::into_raw` instead")]
-    #[inline]
-    pub fn into_raw_non_null(this: Self) -> NonNull<T> {
-        // safe because Arc guarantees its pointer is non-null
-        unsafe { NonNull::new_unchecked(Arc::into_raw(this) as *mut _) }
-    }
-
-    /// Creates a new [`Weak`][weak] pointer to this allocation.
-    ///
-    /// [weak]: struct.Weak.html
     ///
     /// # Examples
     ///
@@ -714,9 +786,7 @@ impl<T: ?Sized> Arc<T> {
         }
     }
 
-    /// Gets the number of [`Weak`][weak] pointers to this allocation.
+    /// Gets the number of [`Weak`] pointers to this allocation.
-    ///
-    /// [weak]: struct.Weak.html
     ///
     /// # Safety
     ///
@@ -885,7 +955,7 @@ impl<T: ?Sized> Arc<T> {
     /// assert!(!Arc::ptr_eq(&five, &other_five));
     /// ```
     ///
-    /// [`ptr::eq`]: ../../std/ptr/fn.eq.html
+    /// [`ptr::eq`]: core::ptr::eq
     pub fn ptr_eq(this: &Self, other: &Self) -> bool {
         this.ptr.as_ptr() == other.ptr.as_ptr()
     }
@@ -899,6 +969,7 @@ impl<T: ?Sized> Arc<T> {
     /// and must return back a (potentially fat)-pointer for the `ArcInner<T>`.
     unsafe fn allocate_for_layout(
         value_layout: Layout,
+        allocate: impl FnOnce(Layout) -> Result<NonNull<[u8]>, AllocErr>,
         mem_to_arcinner: impl FnOnce(*mut u8) -> *mut ArcInner<T>,
     ) -> *mut ArcInner<T> {
         // Calculate layout using the given value layout.
@@ -907,12 +978,10 @@ impl<T: ?Sized> Arc<T> {
         // reference (see #54908).
         let layout = Layout::new::<ArcInner<()>>().extend(value_layout).unwrap().0.pad_to_align();
 
-        let mem = Global
+        let ptr = allocate(layout).unwrap_or_else(|_| handle_alloc_error(layout));
-            .alloc(layout, AllocInit::Uninitialized)
-            .unwrap_or_else(|_| handle_alloc_error(layout));
 
         // Initialize the ArcInner
-        let inner = mem_to_arcinner(mem.ptr.as_ptr());
+        let inner = mem_to_arcinner(ptr.as_non_null_ptr().as_ptr());
         debug_assert_eq!(unsafe { Layout::for_value(&*inner) }, layout);
 
         unsafe {
@@ -927,9 +996,11 @@ impl<T: ?Sized> Arc<T> {
     unsafe fn allocate_for_ptr(ptr: *const T) -> *mut ArcInner<T> {
         // Allocate for the `ArcInner<T>` using the given value.
         unsafe {
-            Self::allocate_for_layout(Layout::for_value(&*ptr), |mem| {
+            Self::allocate_for_layout(
-                set_data_ptr(ptr as *mut T, mem) as *mut ArcInner<T>
+                Layout::for_value(&*ptr),
-            })
+                |layout| Global.alloc(layout),
+                |mem| set_data_ptr(ptr as *mut T, mem) as *mut ArcInner<T>,
+            )
         }
     }
 
@@ -960,9 +1031,11 @@ impl<T> Arc<[T]> {
     /// Allocates an `ArcInner<[T]>` with the given length.
     unsafe fn allocate_for_slice(len: usize) -> *mut ArcInner<[T]> {
         unsafe {
-            Self::allocate_for_layout(Layout::array::<T>(len).unwrap(), |mem| {
+            Self::allocate_for_layout(
-                ptr::slice_from_raw_parts_mut(mem as *mut T, len) as *mut ArcInner<[T]>
+                Layout::array::<T>(len).unwrap(),
-            })
+                |layout| Global.alloc(layout),
+                |mem| ptr::slice_from_raw_parts_mut(mem as *mut T, len) as *mut ArcInner<[T]>,
+            )
         }
     }
 }
@@ -1012,7 +1085,7 @@ impl<T> Arc<[T]> {
                     let slice = from_raw_parts_mut(self.elems, self.n_elems);
                     ptr::drop_in_place(slice);
 
-                    Global.dealloc(self.mem.cast(), self.layout);
+                    Global.dealloc(self.mem, self.layout);
                 }
             }
         }
@@ -1124,7 +1197,7 @@ impl<T: ?Sized> Receiver for Arc<T> {}
 impl<T: Clone> Arc<T> {
     /// Makes a mutable reference into the given `Arc`.
     ///
-    /// If there are other `Arc` or [`Weak`][weak] pointers to the same allocation,
+    /// If there are other `Arc` or [`Weak`] pointers to the same allocation,
     /// then `make_mut` will create a new allocation and invoke [`clone`][clone] on the inner value
     /// to ensure unique ownership. This is also referred to as clone-on-write.
     ///
@@ -1133,10 +1206,9 @@ impl<T: Clone> Arc<T> {
     ///
     /// See also [`get_mut`][get_mut], which will fail rather than cloning.
     ///
-    /// [weak]: struct.Weak.html
+    /// [clone]: Clone::clone
-    /// [clone]: ../../std/clone/trait.Clone.html#tymethod.clone
+    /// [get_mut]: Arc::get_mut
-    /// [get_mut]: struct.Arc.html#method.get_mut
+    /// [`Rc::make_mut`]: super::rc::Rc::make_mut
-    /// [`Rc::make_mut`]: ../rc/struct.Rc.html#method.make_mut
     ///
     /// # Examples
     ///
@@ -1210,18 +1282,16 @@ impl<T: Clone> Arc<T> {
 
 impl<T: ?Sized> Arc<T> {
     /// Returns a mutable reference into the given `Arc`, if there are
-    /// no other `Arc` or [`Weak`][weak] pointers to the same allocation.
+    /// no other `Arc` or [`Weak`] pointers to the same allocation.
     ///
-    /// Returns [`None`][option] otherwise, because it is not safe to
+    /// Returns [`None`] otherwise, because it is not safe to
     /// mutate a shared value.
     ///
     /// See also [`make_mut`][make_mut], which will [`clone`][clone]
     /// the inner value when there are other pointers.
     ///
-    /// [weak]: struct.Weak.html
+    /// [make_mut]: Arc::make_mut
-    /// [option]: ../../std/option/enum.Option.html
+    /// [clone]: Clone::clone
-    /// [make_mut]: struct.Arc.html#method.make_mut
-    /// [clone]: ../../std/clone/trait.Clone.html#tymethod.clone
     ///
     /// # Examples
     ///
@@ -1255,7 +1325,7 @@ impl<T: ?Sized> Arc<T> {
     ///
     /// See also [`get_mut`], which is safe and does appropriate checks.
     ///
-    /// [`get_mut`]: struct.Arc.html#method.get_mut
+    /// [`get_mut`]: Arc::get_mut
     ///
     /// # Safety
     ///
@@ -1341,8 +1411,6 @@ unsafe impl<#[may_dangle] T: ?Sized> Drop for Arc<T> {
     /// drop(foo);    // Doesn't print anything
     /// drop(foo2);   // Prints "dropped!"
     /// ```
-    ///
-    /// [`Weak`]: ../../std/sync/struct.Weak.html
     #[inline]
     fn drop(&mut self) {
         // Because `fetch_sub` is already atomic, we do not need to synchronize
@@ -1427,8 +1495,7 @@ impl<T> Weak<T> {
     /// Constructs a new `Weak<T>`, without allocating any memory.
     /// Calling [`upgrade`] on the return value always gives [`None`].
     ///
-    /// [`upgrade`]: struct.Weak.html#method.upgrade
+    /// [`upgrade`]: Weak::upgrade
-    /// [`None`]: ../../std/option/enum.Option.html#variant.None
     ///
     /// # Examples
     ///
@@ -1467,7 +1534,7 @@ impl<T> Weak<T> {
     /// // assert_eq!("hello", unsafe { &*weak.as_ptr() });
     /// ```
     ///
-    /// [`null`]: ../../std/ptr/fn.null.html
+    /// [`null`]: core::ptr::null
     #[stable(feature = "weak_into_raw", since = "1.45.0")]
     pub fn as_ptr(&self) -> *const T {
         let ptr: *mut ArcInner<T> = NonNull::as_ptr(self.ptr);
@@ -1486,8 +1553,9 @@ impl<T> Weak<T> {
 
     /// Consumes the `Weak<T>` and turns it into a raw pointer.
     ///
-    /// This converts the weak pointer into a raw pointer, preserving the original weak count. It
+    /// This converts the weak pointer into a raw pointer, while still preserving the ownership of
-    /// can be turned back into the `Weak<T>` with [`from_raw`].
+    /// one weak reference (the weak count is not modified by this operation). It can be turned
+    /// back into the `Weak<T>` with [`from_raw`].
     ///
     /// The same restrictions of accessing the target of the pointer as with
     /// [`as_ptr`] apply.
@@ -1508,8 +1576,8 @@ impl<T> Weak<T> {
     /// assert_eq!(0, Arc::weak_count(&strong));
     /// ```
     ///
-    /// [`from_raw`]: struct.Weak.html#method.from_raw
+    /// [`from_raw`]: Weak::from_raw
-    /// [`as_ptr`]: struct.Weak.html#method.as_ptr
+    /// [`as_ptr`]: Weak::as_ptr
     #[stable(feature = "weak_into_raw", since = "1.45.0")]
     pub fn into_raw(self) -> *const T {
         let result = self.as_ptr();
@@ -1517,24 +1585,23 @@ impl<T> Weak<T> {
         result
     }
 
-    /// Converts a raw pointer previously created by [`into_raw`] back into
+    /// Converts a raw pointer previously created by [`into_raw`] back into `Weak<T>`.
-    /// `Weak<T>`.
     ///
     /// This can be used to safely get a strong reference (by calling [`upgrade`]
     /// later) or to deallocate the weak count by dropping the `Weak<T>`.
     ///
-    /// It takes ownership of one weak count (with the exception of pointers created by [`new`],
+    /// It takes ownership of one weak reference (with the exception of pointers created by [`new`],
-    /// as these don't have any corresponding weak count).
+    /// as these don't own anything; the method still works on them).
     ///
     /// # Safety
     ///
     /// The pointer must have originated from the [`into_raw`] and must still own its potential
-    /// weak reference count.
+    /// weak reference.
-    ///
-    /// It is allowed for the strong count to be 0 at the time of calling this, but the weak count
-    /// must be non-zero or the pointer must have originated from a dangling `Weak<T>` (one created
-    /// by [`new`]).
     ///
+    /// It is allowed for the strong count to be 0 at the time of calling this. Nevertheless, this
+    /// takes ownership of one weak reference currently represented as a raw pointer (the weak
+    /// count is not modified by this operation) and therefore it must be paired with a previous
+    /// call to [`into_raw`].
     /// # Examples
     ///
     /// ```
@@ -1556,12 +1623,10 @@ impl<T> Weak<T> {
     /// assert!(unsafe { Weak::from_raw(raw_2) }.upgrade().is_none());
     /// ```
     ///
-    /// [`new`]: struct.Weak.html#method.new
+    /// [`new`]: Weak::new
-    /// [`into_raw`]: struct.Weak.html#method.into_raw
+    /// [`into_raw`]: Weak::into_raw
-    /// [`upgrade`]: struct.Weak.html#method.upgrade
+    /// [`upgrade`]: Weak::upgrade
-    /// [`Weak`]: struct.Weak.html
+    /// [`forget`]: std::mem::forget
-    /// [`Arc`]: struct.Arc.html
-    /// [`forget`]: ../../std/mem/fn.forget.html
     #[stable(feature = "weak_into_raw", since = "1.45.0")]
     pub unsafe fn from_raw(ptr: *const T) -> Self {
         if ptr.is_null() {
@@ -1591,9 +1656,6 @@ impl<T: ?Sized> Weak<T> {
     ///
     /// Returns [`None`] if the inner value has since been dropped.
     ///
-    /// [`Arc`]: struct.Arc.html
-    /// [`None`]: ../../std/option/enum.Option.html#variant.None
-    ///
     /// # Examples
     ///
     /// ```
@@ -1615,7 +1677,8 @@ impl<T: ?Sized> Weak<T> {
     #[stable(feature = "arc_weak", since = "1.4.0")]
     pub fn upgrade(&self) -> Option<Arc<T>> {
         // We use a CAS loop to increment the strong count instead of a
-        // fetch_add because once the count hits 0 it must never be above 0.
+        // fetch_add as this function should never take the reference count
+        // from zero to one.
         let inner = self.inner()?;
 
         // Relaxed load because any write of 0 that we can observe
@@ -1634,8 +1697,11 @@ impl<T: ?Sized> Weak<T> {
                 abort();
             }
 
-            // Relaxed is valid for the same reason it is on Arc's Clone impl
+            // Relaxed is fine for the failure case because we don't have any expectations about the new state.
-            match inner.strong.compare_exchange_weak(n, n + 1, Relaxed, Relaxed) {
+            // Acquire is necessary for the success case to synchronise with `Arc::new_cyclic`, when the inner
+            // value can be initialized after `Weak` references have already been created. In that case, we
+            // expect to observe the fully initialized value.
+            match inner.strong.compare_exchange_weak(n, n + 1, Acquire, Relaxed) {
                 Ok(_) => return Some(Arc::from_inner(self.ptr)), // null checked above
                 Err(old) => n = old,
             }
@@ -1645,8 +1711,6 @@ impl<T: ?Sized> Weak<T> {
     /// Gets the number of strong (`Arc`) pointers pointing to this allocation.
     ///
     /// If `self` was created using [`Weak::new`], this will return 0.
-    ///
-    /// [`Weak::new`]: #method.new
     #[stable(feature = "weak_counts", since = "1.41.0")]
     pub fn strong_count(&self) -> usize {
         if let Some(inner) = self.inner() { inner.strong.load(SeqCst) } else { 0 }
@@ -1663,8 +1727,6 @@ impl<T: ?Sized> Weak<T> {
     /// Due to implementation details, the returned value can be off by 1 in
     /// either direction when other threads are manipulating any `Arc`s or
     /// `Weak`s pointing to the same allocation.
-    ///
-    /// [`Weak::new`]: #method.new
     #[stable(feature = "weak_counts", since = "1.41.0")]
     pub fn weak_count(&self) -> usize {
         self.inner()
@@ -1742,7 +1804,7 @@ impl<T: ?Sized> Weak<T> {
     /// assert!(!first.ptr_eq(&third));
     /// ```
     ///
-    /// [`ptr::eq`]: ../../std/ptr/fn.eq.html
+    /// [`ptr::eq`]: core::ptr::eq
     #[inline]
     #[stable(feature = "weak_ptr_eq", since = "1.39.0")]
     pub fn ptr_eq(&self, other: &Self) -> bool {
@@ -1791,8 +1853,7 @@ impl<T> Default for Weak<T> {
     /// Calling [`upgrade`] on the return value always
     /// gives [`None`].
     ///
-    /// [`None`]: ../../std/option/enum.Option.html#variant.None
+    /// [`upgrade`]: Weak::upgrade
-    /// [`upgrade`]: ../../std/sync/struct.Weak.html#method.upgrade
     ///
     /// # Examples
     ///
@@ -2162,10 +2223,7 @@ where
 }
 
 #[stable(feature = "boxed_slice_try_from", since = "1.43.0")]
-impl<T, const N: usize> TryFrom<Arc<[T]>> for Arc<[T; N]>
+impl<T, const N: usize> TryFrom<Arc<[T]>> for Arc<[T; N]> {
-where
-    [T; N]: LengthAtMost32,
-{
     type Error = Arc<[T]>;
 
     fn try_from(boxed_slice: Arc<[T]>) -> Result<Self, Self::Error> {
@@ -2282,7 +2340,7 @@ impl<T: ?Sized> Unpin for Arc<T> {}
 ///
 /// - This function is safe for any argument if `T` is sized, and
 /// - if `T` is unsized, the pointer must have appropriate pointer metadata
-///   aquired from the real instance that you are getting this offset for.
+///   acquired from the real instance that you are getting this offset for.
 unsafe fn data_offset<T: ?Sized>(ptr: *const T) -> isize {
     // Align the unsized value to the end of the `ArcInner`.
     // Because it is `?Sized`, it will always be the last field in memory.

library/alloc/src/sync/tests.rs

@@ -0,0 +1,561 @@
+use super::*;
+
+use std::boxed::Box;
+use std::clone::Clone;
+use std::convert::{From, TryInto};
+use std::mem::drop;
+use std::ops::Drop;
+use std::option::Option::{self, None, Some};
+use std::sync::atomic::{
+    self,
+    Ordering::{Acquire, SeqCst},
+};
+use std::sync::mpsc::channel;
+use std::sync::Mutex;
+use std::thread;
+
+use crate::vec::Vec;
+
+struct Canary(*mut atomic::AtomicUsize);
+
+impl Drop for Canary {
+    fn drop(&mut self) {
+        unsafe {
+            match *self {
+                Canary(c) => {
+                    (*c).fetch_add(1, SeqCst);
+                }
+            }
+        }
+    }
+}
+
+#[test]
+#[cfg_attr(target_os = "emscripten", ignore)]
+fn manually_share_arc() {
+    let v = vec![1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
+    let arc_v = Arc::new(v);
+
+    let (tx, rx) = channel();
+
+    let _t = thread::spawn(move || {
+        let arc_v: Arc<Vec<i32>> = rx.recv().unwrap();
+        assert_eq!((*arc_v)[3], 4);
+    });
+
+    tx.send(arc_v.clone()).unwrap();
+
+    assert_eq!((*arc_v)[2], 3);
+    assert_eq!((*arc_v)[4], 5);
+}
+
+#[test]
+fn test_arc_get_mut() {
+    let mut x = Arc::new(3);
+    *Arc::get_mut(&mut x).unwrap() = 4;
+    assert_eq!(*x, 4);
+    let y = x.clone();
+    assert!(Arc::get_mut(&mut x).is_none());
+    drop(y);
+    assert!(Arc::get_mut(&mut x).is_some());
+    let _w = Arc::downgrade(&x);
+    assert!(Arc::get_mut(&mut x).is_none());
+}
+
+#[test]
+fn weak_counts() {
+    assert_eq!(Weak::weak_count(&Weak::<u64>::new()), 0);
+    assert_eq!(Weak::strong_count(&Weak::<u64>::new()), 0);
+
+    let a = Arc::new(0);
+    let w = Arc::downgrade(&a);
+    assert_eq!(Weak::strong_count(&w), 1);
+    assert_eq!(Weak::weak_count(&w), 1);
+    let w2 = w.clone();
+    assert_eq!(Weak::strong_count(&w), 1);
+    assert_eq!(Weak::weak_count(&w), 2);
+    assert_eq!(Weak::strong_count(&w2), 1);
+    assert_eq!(Weak::weak_count(&w2), 2);
+    drop(w);
+    assert_eq!(Weak::strong_count(&w2), 1);
+    assert_eq!(Weak::weak_count(&w2), 1);
+    let a2 = a.clone();
+    assert_eq!(Weak::strong_count(&w2), 2);
+    assert_eq!(Weak::weak_count(&w2), 1);
+    drop(a2);
+    drop(a);
+    assert_eq!(Weak::strong_count(&w2), 0);
+    assert_eq!(Weak::weak_count(&w2), 0);
+    drop(w2);
+}
+
+#[test]
+fn try_unwrap() {
+    let x = Arc::new(3);
+    assert_eq!(Arc::try_unwrap(x), Ok(3));
+    let x = Arc::new(4);
+    let _y = x.clone();
+    assert_eq!(Arc::try_unwrap(x), Err(Arc::new(4)));
+    let x = Arc::new(5);
+    let _w = Arc::downgrade(&x);
+    assert_eq!(Arc::try_unwrap(x), Ok(5));
+}
+
+#[test]
+fn into_from_raw() {
+    let x = Arc::new(box "hello");
+    let y = x.clone();
+
+    let x_ptr = Arc::into_raw(x);
+    drop(y);
+    unsafe {
+        assert_eq!(**x_ptr, "hello");
+
+        let x = Arc::from_raw(x_ptr);
+        assert_eq!(**x, "hello");
+
+        assert_eq!(Arc::try_unwrap(x).map(|x| *x), Ok("hello"));
+    }
+}
+
+#[test]
+fn test_into_from_raw_unsized() {
+    use std::fmt::Display;
+    use std::string::ToString;
+
+    let arc: Arc<str> = Arc::from("foo");
+
+    let ptr = Arc::into_raw(arc.clone());
+    let arc2 = unsafe { Arc::from_raw(ptr) };
+
+    assert_eq!(unsafe { &*ptr }, "foo");
+    assert_eq!(arc, arc2);
+
+    let arc: Arc<dyn Display> = Arc::new(123);
+
+    let ptr = Arc::into_raw(arc.clone());
+    let arc2 = unsafe { Arc::from_raw(ptr) };
+
+    assert_eq!(unsafe { &*ptr }.to_string(), "123");
+    assert_eq!(arc2.to_string(), "123");
+}
+
+#[test]
+fn test_cowarc_clone_make_mut() {
+    let mut cow0 = Arc::new(75);
+    let mut cow1 = cow0.clone();
+    let mut cow2 = cow1.clone();
+
+    assert!(75 == *Arc::make_mut(&mut cow0));
+    assert!(75 == *Arc::make_mut(&mut cow1));
+    assert!(75 == *Arc::make_mut(&mut cow2));
+
+    *Arc::make_mut(&mut cow0) += 1;
+    *Arc::make_mut(&mut cow1) += 2;
+    *Arc::make_mut(&mut cow2) += 3;
+
+    assert!(76 == *cow0);
+    assert!(77 == *cow1);
+    assert!(78 == *cow2);
+
+    // none should point to the same backing memory
+    assert!(*cow0 != *cow1);
+    assert!(*cow0 != *cow2);
+    assert!(*cow1 != *cow2);
+}
+
+#[test]
+fn test_cowarc_clone_unique2() {
+    let mut cow0 = Arc::new(75);
+    let cow1 = cow0.clone();
+    let cow2 = cow1.clone();
+
+    assert!(75 == *cow0);
+    assert!(75 == *cow1);
+    assert!(75 == *cow2);
+
+    *Arc::make_mut(&mut cow0) += 1;
+    assert!(76 == *cow0);
+    assert!(75 == *cow1);
+    assert!(75 == *cow2);
+
+    // cow1 and cow2 should share the same contents
+    // cow0 should have a unique reference
+    assert!(*cow0 != *cow1);
+    assert!(*cow0 != *cow2);
+    assert!(*cow1 == *cow2);
+}
+
+#[test]
+fn test_cowarc_clone_weak() {
+    let mut cow0 = Arc::new(75);
+    let cow1_weak = Arc::downgrade(&cow0);
+
+    assert!(75 == *cow0);
+    assert!(75 == *cow1_weak.upgrade().unwrap());
+
+    *Arc::make_mut(&mut cow0) += 1;
+
+    assert!(76 == *cow0);
+    assert!(cow1_weak.upgrade().is_none());
+}
+
+#[test]
+fn test_live() {
+    let x = Arc::new(5);
+    let y = Arc::downgrade(&x);
+    assert!(y.upgrade().is_some());
+}
+
+#[test]
+fn test_dead() {
+    let x = Arc::new(5);
+    let y = Arc::downgrade(&x);
+    drop(x);
+    assert!(y.upgrade().is_none());
+}
+
+#[test]
+fn weak_self_cyclic() {
+    struct Cycle {
+        x: Mutex<Option<Weak<Cycle>>>,
+    }
+
+    let a = Arc::new(Cycle { x: Mutex::new(None) });
+    let b = Arc::downgrade(&a.clone());
+    *a.x.lock().unwrap() = Some(b);
+
+    // hopefully we don't double-free (or leak)...
+}
+
+#[test]
+fn drop_arc() {
+    let mut canary = atomic::AtomicUsize::new(0);
+    let x = Arc::new(Canary(&mut canary as *mut atomic::AtomicUsize));
+    drop(x);
+    assert!(canary.load(Acquire) == 1);
+}
+
+#[test]
+fn drop_arc_weak() {
+    let mut canary = atomic::AtomicUsize::new(0);
+    let arc = Arc::new(Canary(&mut canary as *mut atomic::AtomicUsize));
+    let arc_weak = Arc::downgrade(&arc);
+    assert!(canary.load(Acquire) == 0);
+    drop(arc);
+    assert!(canary.load(Acquire) == 1);
+    drop(arc_weak);
+}
+
+#[test]
+fn test_strong_count() {
+    let a = Arc::new(0);
+    assert!(Arc::strong_count(&a) == 1);
+    let w = Arc::downgrade(&a);
+    assert!(Arc::strong_count(&a) == 1);
+    let b = w.upgrade().expect("");
+    assert!(Arc::strong_count(&b) == 2);
+    assert!(Arc::strong_count(&a) == 2);
+    drop(w);
+    drop(a);
+    assert!(Arc::strong_count(&b) == 1);
+    let c = b.clone();
+    assert!(Arc::strong_count(&b) == 2);
+    assert!(Arc::strong_count(&c) == 2);
+}
+
+#[test]
+fn test_weak_count() {
+    let a = Arc::new(0);
+    assert!(Arc::strong_count(&a) == 1);
+    assert!(Arc::weak_count(&a) == 0);
+    let w = Arc::downgrade(&a);
+    assert!(Arc::strong_count(&a) == 1);
+    assert!(Arc::weak_count(&a) == 1);
+    let x = w.clone();
+    assert!(Arc::weak_count(&a) == 2);
+    drop(w);
+    drop(x);
+    assert!(Arc::strong_count(&a) == 1);
+    assert!(Arc::weak_count(&a) == 0);
+    let c = a.clone();
+    assert!(Arc::strong_count(&a) == 2);
+    assert!(Arc::weak_count(&a) == 0);
+    let d = Arc::downgrade(&c);
+    assert!(Arc::weak_count(&c) == 1);
+    assert!(Arc::strong_count(&c) == 2);
+
+    drop(a);
+    drop(c);
+    drop(d);
+}
+
+#[test]
+fn show_arc() {
+    let a = Arc::new(5);
+    assert_eq!(format!("{:?}", a), "5");
+}
+
+// Make sure deriving works with Arc<T>
+#[derive(Eq, Ord, PartialEq, PartialOrd, Clone, Debug, Default)]
+struct Foo {
+    inner: Arc<i32>,
+}
+
+#[test]
+fn test_unsized() {
+    let x: Arc<[i32]> = Arc::new([1, 2, 3]);
+    assert_eq!(format!("{:?}", x), "[1, 2, 3]");
+    let y = Arc::downgrade(&x.clone());
+    drop(x);
+    assert!(y.upgrade().is_none());
+}
+
+#[test]
+fn test_from_owned() {
+    let foo = 123;
+    let foo_arc = Arc::from(foo);
+    assert!(123 == *foo_arc);
+}
+
+#[test]
+fn test_new_weak() {
+    let foo: Weak<usize> = Weak::new();
+    assert!(foo.upgrade().is_none());
+}
+
+#[test]
+fn test_ptr_eq() {
+    let five = Arc::new(5);
+    let same_five = five.clone();
+    let other_five = Arc::new(5);
+
+    assert!(Arc::ptr_eq(&five, &same_five));
+    assert!(!Arc::ptr_eq(&five, &other_five));
+}
+
+#[test]
+#[cfg_attr(target_os = "emscripten", ignore)]
+fn test_weak_count_locked() {
+    let mut a = Arc::new(atomic::AtomicBool::new(false));
+    let a2 = a.clone();
+    let t = thread::spawn(move || {
+        // Miri is too slow
+        let count = if cfg!(miri) { 1000 } else { 1000000 };
+        for _i in 0..count {
+            Arc::get_mut(&mut a);
+        }
+        a.store(true, SeqCst);
+    });
+
+    while !a2.load(SeqCst) {
+        let n = Arc::weak_count(&a2);
+        assert!(n < 2, "bad weak count: {}", n);
+        #[cfg(miri)] // Miri's scheduler does not guarantee liveness, and thus needs this hint.
+        atomic::spin_loop_hint();
+    }
+    t.join().unwrap();
+}
+
+#[test]
+fn test_from_str() {
+    let r: Arc<str> = Arc::from("foo");
+
+    assert_eq!(&r[..], "foo");
+}
+
+#[test]
+fn test_copy_from_slice() {
+    let s: &[u32] = &[1, 2, 3];
+    let r: Arc<[u32]> = Arc::from(s);
+
+    assert_eq!(&r[..], [1, 2, 3]);
+}
+
+#[test]
+fn test_clone_from_slice() {
+    #[derive(Clone, Debug, Eq, PartialEq)]
+    struct X(u32);
+
+    let s: &[X] = &[X(1), X(2), X(3)];
+    let r: Arc<[X]> = Arc::from(s);
+
+    assert_eq!(&r[..], s);
+}
+
+#[test]
+#[should_panic]
+fn test_clone_from_slice_panic() {
+    use std::string::{String, ToString};
+
+    struct Fail(u32, String);
+
+    impl Clone for Fail {
+        fn clone(&self) -> Fail {
+            if self.0 == 2 {
+                panic!();
+            }
+            Fail(self.0, self.1.clone())
+        }
+    }
+
+    let s: &[Fail] =
+        &[Fail(0, "foo".to_string()), Fail(1, "bar".to_string()), Fail(2, "baz".to_string())];
+
+    // Should panic, but not cause memory corruption
+    let _r: Arc<[Fail]> = Arc::from(s);
+}
+
+#[test]
+fn test_from_box() {
+    let b: Box<u32> = box 123;
+    let r: Arc<u32> = Arc::from(b);
+
+    assert_eq!(*r, 123);
+}
+
+#[test]
+fn test_from_box_str() {
+    use std::string::String;
+
+    let s = String::from("foo").into_boxed_str();
+    let r: Arc<str> = Arc::from(s);
+
+    assert_eq!(&r[..], "foo");
+}
+
+#[test]
+fn test_from_box_slice() {
+    let s = vec![1, 2, 3].into_boxed_slice();
+    let r: Arc<[u32]> = Arc::from(s);
+
+    assert_eq!(&r[..], [1, 2, 3]);
+}
+
+#[test]
+fn test_from_box_trait() {
+    use std::fmt::Display;
+    use std::string::ToString;
+
+    let b: Box<dyn Display> = box 123;
+    let r: Arc<dyn Display> = Arc::from(b);
+
+    assert_eq!(r.to_string(), "123");
+}
+
+#[test]
+fn test_from_box_trait_zero_sized() {
+    use std::fmt::Debug;
+
+    let b: Box<dyn Debug> = box ();
+    let r: Arc<dyn Debug> = Arc::from(b);
+
+    assert_eq!(format!("{:?}", r), "()");
+}
+
+#[test]
+fn test_from_vec() {
+    let v = vec![1, 2, 3];
+    let r: Arc<[u32]> = Arc::from(v);
+
+    assert_eq!(&r[..], [1, 2, 3]);
+}
+
+#[test]
+fn test_downcast() {
+    use std::any::Any;
+
+    let r1: Arc<dyn Any + Send + Sync> = Arc::new(i32::MAX);
+    let r2: Arc<dyn Any + Send + Sync> = Arc::new("abc");
+
+    assert!(r1.clone().downcast::<u32>().is_err());
+
+    let r1i32 = r1.downcast::<i32>();
+    assert!(r1i32.is_ok());
+    assert_eq!(r1i32.unwrap(), Arc::new(i32::MAX));
+
+    assert!(r2.clone().downcast::<i32>().is_err());
+
+    let r2str = r2.downcast::<&'static str>();
+    assert!(r2str.is_ok());
+    assert_eq!(r2str.unwrap(), Arc::new("abc"));
+}
+
+#[test]
+fn test_array_from_slice() {
+    let v = vec![1, 2, 3];
+    let r: Arc<[u32]> = Arc::from(v);
+
+    let a: Result<Arc<[u32; 3]>, _> = r.clone().try_into();
+    assert!(a.is_ok());
+
+    let a: Result<Arc<[u32; 2]>, _> = r.clone().try_into();
+    assert!(a.is_err());
+}
+
+#[test]
+fn test_arc_cyclic_with_zero_refs() {
+    struct ZeroRefs {
+        inner: Weak<ZeroRefs>,
+    }
+    let zero_refs = Arc::new_cyclic(|inner| {
+        assert_eq!(inner.strong_count(), 0);
+        assert!(inner.upgrade().is_none());
+        ZeroRefs { inner: Weak::new() }
+    });
+
+    assert_eq!(Arc::strong_count(&zero_refs), 1);
+    assert_eq!(Arc::weak_count(&zero_refs), 0);
+    assert_eq!(zero_refs.inner.strong_count(), 0);
+    assert_eq!(zero_refs.inner.weak_count(), 0);
+}
+
+#[test]
+fn test_arc_new_cyclic_one_ref() {
+    struct OneRef {
+        inner: Weak<OneRef>,
+    }
+    let one_ref = Arc::new_cyclic(|inner| {
+        assert_eq!(inner.strong_count(), 0);
+        assert!(inner.upgrade().is_none());
+        OneRef { inner: inner.clone() }
+    });
+
+    assert_eq!(Arc::strong_count(&one_ref), 1);
+    assert_eq!(Arc::weak_count(&one_ref), 1);
+
+    let one_ref2 = Weak::upgrade(&one_ref.inner).unwrap();
+    assert!(Arc::ptr_eq(&one_ref, &one_ref2));
+
+    assert_eq!(Arc::strong_count(&one_ref), 2);
+    assert_eq!(Arc::weak_count(&one_ref), 1);
+}
+
+#[test]
+fn test_arc_cyclic_two_refs() {
+    struct TwoRefs {
+        inner1: Weak<TwoRefs>,
+        inner2: Weak<TwoRefs>,
+    }
+    let two_refs = Arc::new_cyclic(|inner| {
+        assert_eq!(inner.strong_count(), 0);
+        assert!(inner.upgrade().is_none());
+
+        let inner1 = inner.clone();
+        let inner2 = inner1.clone();
+
+        TwoRefs { inner1, inner2 }
+    });
+
+    assert_eq!(Arc::strong_count(&two_refs), 1);
+    assert_eq!(Arc::weak_count(&two_refs), 2);
+
+    let two_refs1 = Weak::upgrade(&two_refs.inner1).unwrap();
+    assert!(Arc::ptr_eq(&two_refs, &two_refs1));
+
+    let two_refs2 = Weak::upgrade(&two_refs.inner2).unwrap();
+    assert!(Arc::ptr_eq(&two_refs, &two_refs2));
+
+    assert_eq!(Arc::strong_count(&two_refs), 3);
+    assert_eq!(Arc::weak_count(&two_refs), 2);
+}

library/alloc/src/task.rs

@@ -13,11 +13,9 @@ use crate::sync::Arc;
 ///
 /// This trait is a memory-safe and ergonomic alternative to constructing a
 /// [`RawWaker`]. It supports the common executor design in which the data used
-/// to wake up a task is stored in an [`Arc`][arc]. Some executors (especially
+/// to wake up a task is stored in an [`Arc`]. Some executors (especially
 /// those for embedded systems) cannot use this API, which is why [`RawWaker`]
 /// exists as an alternative for those systems.
-///
-/// [arc]: ../../std/sync/struct.Arc.html
 #[unstable(feature = "wake_trait", issue = "69912")]
 pub trait Wake {
     /// Wake this task.
@@ -69,14 +67,13 @@ fn raw_waker<W: Wake + Send + Sync + 'static>(waker: Arc<W>) -> RawWaker {
 
     // Wake by value, moving the Arc into the Wake::wake function
     unsafe fn wake<W: Wake + Send + Sync + 'static>(waker: *const ()) {
-        let waker: Arc<W> = unsafe { Arc::from_raw(waker as *const W) };
+        let waker = unsafe { Arc::from_raw(waker as *const W) };
         <W as Wake>::wake(waker);
     }
 
     // Wake by reference, wrap the waker in ManuallyDrop to avoid dropping it
     unsafe fn wake_by_ref<W: Wake + Send + Sync + 'static>(waker: *const ()) {
-        let waker: ManuallyDrop<Arc<W>> =
+        let waker = unsafe { ManuallyDrop::new(Arc::from_raw(waker as *const W)) };
-            unsafe { ManuallyDrop::new(Arc::from_raw(waker as *const W)) };
         <W as Wake>::wake_by_ref(&waker);
     }
 

library/alloc/tests/boxed.rs

@@ -0,0 +1,51 @@
+use std::mem::MaybeUninit;
+use std::ptr::NonNull;
+
+#[test]
+fn unitialized_zero_size_box() {
+    assert_eq!(
+        &*Box::<()>::new_uninit() as *const _,
+        NonNull::<MaybeUninit<()>>::dangling().as_ptr(),
+    );
+    assert_eq!(
+        Box::<[()]>::new_uninit_slice(4).as_ptr(),
+        NonNull::<MaybeUninit<()>>::dangling().as_ptr(),
+    );
+    assert_eq!(
+        Box::<[String]>::new_uninit_slice(0).as_ptr(),
+        NonNull::<MaybeUninit<String>>::dangling().as_ptr(),
+    );
+}
+
+#[derive(Clone, PartialEq, Eq, Debug)]
+struct Dummy {
+    _data: u8,
+}
+
+#[test]
+fn box_clone_and_clone_from_equivalence() {
+    for size in (0..8).map(|i| 2usize.pow(i)) {
+        let control = vec![Dummy { _data: 42 }; size].into_boxed_slice();
+        let clone = control.clone();
+        let mut copy = vec![Dummy { _data: 84 }; size].into_boxed_slice();
+        copy.clone_from(&control);
+        assert_eq!(control, clone);
+        assert_eq!(control, copy);
+    }
+}
+
+/// This test might give a false positive in case the box realocates, but the alocator keeps the
+/// original pointer.
+///
+/// On the other hand it won't give a false negative, if it fails than the memory was definitely not
+/// reused
+#[test]
+fn box_clone_from_ptr_stability() {
+    for size in (0..8).map(|i| 2usize.pow(i)) {
+        let control = vec![Dummy { _data: 42 }; size].into_boxed_slice();
+        let mut copy = vec![Dummy { _data: 84 }; size].into_boxed_slice();
+        let copy_raw = copy.as_ptr() as usize;
+        copy.clone_from(&control);
+        assert_eq!(copy.as_ptr() as usize, copy_raw);
+    }
+}

library/alloc/tests/btree_set_hash.rs

@@ -0,0 +1,19 @@
+use std::collections::BTreeSet;
+
+#[test]
+fn test_hash() {
+    use crate::hash;
+
+    let mut x = BTreeSet::new();
+    let mut y = BTreeSet::new();
+
+    x.insert(1);
+    x.insert(2);
+    x.insert(3);
+
+    y.insert(3);
+    y.insert(2);
+    y.insert(1);
+
+    assert_eq!(hash(&x), hash(&y));
+}

library/alloc/tests/heap.rs

@@ -0,0 +1,44 @@
+use std::alloc::{AllocRef, Global, Layout, System};
+
+/// Issue #45955 and #62251.
+#[test]
+fn alloc_system_overaligned_request() {
+    check_overalign_requests(System)
+}
+
+#[test]
+fn std_heap_overaligned_request() {
+    check_overalign_requests(Global)
+}
+
+fn check_overalign_requests<T: AllocRef>(mut allocator: T) {
+    for &align in &[4, 8, 16, 32] {
+        // less than and bigger than `MIN_ALIGN`
+        for &size in &[align / 2, align - 1] {
+            // size less than alignment
+            let iterations = 128;
+            unsafe {
+                let pointers: Vec<_> = (0..iterations)
+                    .map(|_| {
+                        allocator.alloc(Layout::from_size_align(size, align).unwrap()).unwrap()
+                    })
+                    .collect();
+                for &ptr in &pointers {
+                    assert_eq!(
+                        (ptr.as_non_null_ptr().as_ptr() as usize) % align,
+                        0,
+                        "Got a pointer less aligned than requested"
+                    )
+                }
+
+                // Clean up
+                for &ptr in &pointers {
+                    allocator.dealloc(
+                        ptr.as_non_null_ptr(),
+                        Layout::from_size_align(size, align).unwrap(),
+                    )
+                }
+            }
+        }
+    }
+}

library/alloc/tests/lib.rs

@@ -0,0 +1,57 @@
+#![feature(allocator_api)]
+#![feature(box_syntax)]
+#![feature(drain_filter)]
+#![feature(exact_size_is_empty)]
+#![feature(new_uninit)]
+#![feature(pattern)]
+#![feature(str_split_once)]
+#![feature(trusted_len)]
+#![feature(try_reserve)]
+#![feature(unboxed_closures)]
+#![feature(associated_type_bounds)]
+#![feature(binary_heap_into_iter_sorted)]
+#![feature(binary_heap_drain_sorted)]
+#![feature(slice_ptr_get)]
+#![feature(split_inclusive)]
+#![feature(binary_heap_retain)]
+
+use std::collections::hash_map::DefaultHasher;
+use std::hash::{Hash, Hasher};
+
+mod arc;
+mod binary_heap;
+mod borrow;
+mod boxed;
+mod btree_set_hash;
+mod cow_str;
+mod fmt;
+mod heap;
+mod linked_list;
+mod rc;
+mod slice;
+mod str;
+mod string;
+mod vec;
+mod vec_deque;
+
+fn hash<T: Hash>(t: &T) -> u64 {
+    let mut s = DefaultHasher::new();
+    t.hash(&mut s);
+    s.finish()
+}
+
+// FIXME: Instantiated functions with i128 in the signature is not supported in Emscripten.
+// See https://github.com/kripken/emscripten-fastcomp/issues/169
+#[cfg(not(target_os = "emscripten"))]
+#[test]
+fn test_boxed_hasher() {
+    let ordinary_hash = hash(&5u32);
+
+    let mut hasher_1 = Box::new(DefaultHasher::new());
+    5u32.hash(&mut hasher_1);
+    assert_eq!(ordinary_hash, hasher_1.finish());
+
+    let mut hasher_2 = Box::new(DefaultHasher::new()) as Box<dyn Hasher>;
+    5u32.hash(&mut hasher_2);
+    assert_eq!(ordinary_hash, hasher_2.finish());
+}

library/backtrace/.github/workflows/main.yml

@@ -0,0 +1,194 @@
+name: CI
+
+on:
+  push:
+    branches:
+    - master
+  pull_request:
+    branches:
+    - master
+
+jobs:
+  test:
+    name: Test
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix:
+        thing: [stable, beta, nightly, macos, windows-msvc64, windows-msvc32, windows-gnu64, windows-gnu32]
+        include:
+          - thing: stable
+            os: ubuntu-latest
+            rust: stable
+          - thing: beta
+            os: ubuntu-latest
+            rust: beta
+          - thing: nightly
+            os: ubuntu-latest
+            rust: nightly
+          - thing: macos
+            os: macos-latest
+            rust: stable
+          # Note that these are on nightly due to rust-lang/rust#63700 not being
+          # on stable yet
+          - thing: windows-msvc64
+            os: windows-latest
+            rust: stable-x86_64-msvc
+          - thing: windows-msvc32
+            os: windows-latest
+            rust: stable-i686-msvc
+          - thing: windows-gnu64
+            os: windows-latest
+            rust: stable-x86_64-gnu
+          - thing: windows-gnu32
+            os: windows-latest
+            rust: stable-i686-gnu
+    steps:
+    - uses: actions/checkout@v1
+      with:
+        submodules: true
+    - name: Install Rust (rustup)
+      run: rustup update ${{ matrix.rust }} --no-self-update && rustup default ${{ matrix.rust }}
+      shell: bash
+    # full fidelity of backtraces on 32-bit msvc requires frame pointers, so
+    # enable that for our tests
+    - name: Force frame pointers
+      run: echo "##[set-env name=RUSTFLAGS]-Cforce-frame-pointers"
+      shell: bash
+      if: matrix.thing == 'windows-msvc32'
+    - run: cargo build --manifest-path crates/backtrace-sys/Cargo.toml
+    - run: cargo build
+    - run: cargo test
+    - run: cargo test --features "gimli-symbolize"
+    - run: cargo test --features "libbacktrace"
+    - run: cargo test --features "libbacktrace gimli-symbolize"
+    - run: cargo test --features "serialize-rustc"
+    - run: cargo test --features "serialize-serde"
+    - run: cargo test --features "verify-winapi"
+    - run: cargo test --features "cpp_demangle"
+    - run: cargo test --no-default-features
+    - run: cargo test --no-default-features --features "libbacktrace"
+    - run: cargo test --no-default-features --features "gimli-symbolize"
+    - run: cargo test --no-default-features --features "gimli-symbolize libbacktrace"
+    - run: cargo test --no-default-features --features "libbacktrace std"
+    - run: cargo test --no-default-features --features "gimli-symbolize std"
+    - run: cargo test --no-default-features --features "std"
+    - run: cargo test --manifest-path crates/cpp_smoke_test/Cargo.toml
+    - run: cargo test --manifest-path crates/macos_frames_test/Cargo.toml
+    - run: cargo test --features libbacktrace --manifest-path crates/without_debuginfo/Cargo.toml
+    - run: cargo test --features gimli-symbolize --manifest-path crates/without_debuginfo/Cargo.toml
+    - run: cargo test --manifest-path crates/line-tables-only/Cargo.toml --features libbacktrace
+    - run: cargo test --manifest-path crates/line-tables-only/Cargo.toml --features gimli-symbolize
+    - run: RUSTFLAGS="-C link-arg=-Wl,--compress-debug-sections=zlib-gabi" cargo test --features gimli-symbolize
+      if: contains(matrix.os, 'ubuntu')
+    - run: RUSTFLAGS="-C link-arg=-Wl,--compress-debug-sections=zlib-gnu" cargo test --features gimli-symbolize
+      if: contains(matrix.os, 'ubuntu')
+    - run: cargo build --manifest-path crates/as-if-std/Cargo.toml
+
+  windows_arm64:
+    name: Windows AArch64
+    runs-on: windows-latest
+    steps:
+    - uses: actions/checkout@v1
+      with:
+        submodules: true
+    - name: Install Rust
+      run: rustup update stable --no-self-update && rustup default stable
+      shell: bash
+    - run: rustup target add aarch64-pc-windows-msvc
+    - run: cargo test --no-run --target aarch64-pc-windows-msvc
+    - run: cargo test --no-run --target aarch64-pc-windows-msvc --features verify-winapi
+
+  ios:
+    name: iOS
+    runs-on: macos-latest
+    strategy:
+      matrix:
+        target:
+        - aarch64-apple-ios
+        - x86_64-apple-ios
+        include:
+        - target: aarch64-apple-ios
+          sdk: iphoneos
+        - target: x86_64-apple-ios
+          sdk: iphonesimulator
+    steps:
+    - uses: actions/checkout@v1
+      with:
+        submodules: true
+    - name: Install Rust (
+      run: |
+        curl https://sh.rustup.rs | sh -s -- -y
+        echo "##[add-path]$HOME/.cargo/bin"
+    - run: rustup target add ${{ matrix.target }}
+    - run: |
+        export SDK_PATH=`xcrun --show-sdk-path --sdk ${{ matrix.sdk }}`
+        export RUSTFLAGS="-C link-arg=-isysroot -C link-arg=$SDK_PATH"
+        cargo test --no-run --target ${{ matrix.target }}
+      name: Build tests
+
+  docker:
+    name: Docker
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        target:
+        - aarch64-unknown-linux-gnu
+        - arm-unknown-linux-gnueabihf
+        - armv7-unknown-linux-gnueabihf
+        - i586-unknown-linux-gnu
+        - i686-unknown-linux-gnu
+        - powerpc64-unknown-linux-gnu
+        - x86_64-pc-windows-gnu
+        - x86_64-unknown-linux-gnu
+        - x86_64-unknown-linux-musl
+        - arm-linux-androideabi
+        - armv7-linux-androideabi
+        - aarch64-linux-android
+        - i686-linux-android
+        - x86_64-linux-android
+    steps:
+    - uses: actions/checkout@v1
+      with:
+        submodules: true
+    - name: Install Rust
+      run: rustup update stable && rustup default stable
+    - run: rustup target add ${{ matrix.target }}
+    - run: cargo generate-lockfile
+    - run: ./ci/run-docker.sh ${{ matrix.target }}
+
+  rustfmt:
+    name: Rustfmt
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v1
+      with:
+        submodules: true
+    - name: Install Rust
+      run: rustup update stable && rustup default stable && rustup component add rustfmt
+    - run: cargo fmt --all -- --check
+
+  build:
+    name: Build Targets
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        target: [wasm32-unknown-unknown, wasm32-wasi, x86_64-fuchsia, x86_64-fortanix-unknown-sgx]
+    steps:
+    - uses: actions/checkout@v1
+      with:
+        submodules: true
+    - name: Install Rust
+      run: rustup update nightly && rustup default nightly
+    - run: rustup target add ${{ matrix.target }}
+    - run: cargo build --target ${{ matrix.target }}
+
+  msrv:
+    name: MSRV
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v1
+      with:
+        submodules: true
+    - name: Install Rust
+      run: rustup update 1.40.0 && rustup default 1.40.0
+    - run: cargo build

library/backtrace/Cargo.toml

@@ -0,0 +1,135 @@
+[package]
+name = "backtrace"
+version = "0.3.50"
+authors = ["The Rust Project Developers"]
+license = "MIT/Apache-2.0"
+readme = "README.md"
+repository = "https://github.com/rust-lang/backtrace-rs"
+homepage = "https://github.com/rust-lang/backtrace-rs"
+documentation = "https://docs.rs/backtrace"
+description = """
+A library to acquire a stack trace (backtrace) at runtime in a Rust program.
+"""
+autoexamples = true
+autotests = true
+edition = "2018"
+
+[workspace]
+members = ['crates/cpp_smoke_test', 'crates/as-if-std']
+exclude = ['crates/without_debuginfo', 'crates/macos_frames_test', 'crates/line-tables-only']
+
+[dependencies]
+cfg-if = "0.1.10"
+rustc-demangle = "0.1.4"
+backtrace-sys = { path = "crates/backtrace-sys", version = "0.1.35", optional = true, default_features = false }
+libc = { version = "0.2.45", default-features = false }
+
+# Optionally enable the ability to serialize a `Backtrace`, controlled through
+# the `serialize-*` features below.
+serde = { version = "1.0", optional = true, features = ['derive'] }
+rustc-serialize = { version = "0.3", optional = true }
+
+# Optionally demangle C++ frames' symbols in backtraces.
+cpp_demangle = { default-features = false, version = "0.3.0", optional = true }
+
+
+# Optional dependencies enabled through the `gimli-symbolize` feature, do not
+# use these features directly.
+addr2line = { version = "0.13.0", optional = true, default-features = false }
+miniz_oxide = { version = "0.4.0", optional = true, default-features = false }
+[dependencies.object]
+version = "0.20.0"
+optional = true
+default-features = false
+features = ['read_core', 'elf', 'macho', 'pe', 'unaligned']
+
+[target.'cfg(windows)'.dependencies]
+winapi = { version = "0.3.3", optional = true }
+
+[dev-dependencies]
+dylib-dep = { path = "crates/dylib-dep" }
+libloading = "0.6"
+
+[features]
+# By default libstd support and gimli-symbolize is used to symbolize addresses.
+default = ["std", "gimli-symbolize"]
+
+# Include std support. This enables types like `Backtrace`.
+std = []
+
+#=======================================
+# Methods of resolving symbols
+#
+# - gimli-symbolize: use the `gimli-rs/addr2line` crate to symbolicate
+#   addresses into file, line, and name using DWARF debug information.
+# - libbacktrace: this feature activates the `backtrace-sys` dependency,
+#   building the libbacktrace library found in gcc repos.
+#
+# Note that MSVC unconditionally uses the dbghelp library to symbolize and won't
+# be affected by feature selection here. Also note that it's highly unlikely you
+# want to configure this. If you're having trouble getting backtraces it's
+# likely best to open an issue.
+gimli-symbolize = ["addr2line", "miniz_oxide", "object"]
+libbacktrace = ["backtrace-sys/backtrace-sys"]
+
+#=======================================
+# Methods of serialization
+#
+# Various features used for enabling rustc-serialize or syntex codegen.
+serialize-rustc = ["rustc-serialize"]
+serialize-serde = ["serde"]
+
+#=======================================
+# Deprecated/internal features
+#
+# Only here for backwards compatibility purposes or for internal testing
+# purposes. New code should use none of these features.
+coresymbolication = []
+dladdr = []
+kernel32 = []
+unix-backtrace = []
+libunwind = []
+dbghelp = []
+verify-winapi = [
+  'winapi/dbghelp',
+  'winapi/handleapi',
+  'winapi/libloaderapi',
+  'winapi/memoryapi',
+  'winapi/minwindef',
+  'winapi/processthreadsapi',
+  'winapi/synchapi',
+  'winapi/tlhelp32',
+  'winapi/winbase',
+  'winapi/winnt',
+]
+
+[[example]]
+name = "backtrace"
+required-features = ["std"]
+
+[[example]]
+name = "raw"
+required-features = ["std"]
+
+[[test]]
+name = "skip_inner_frames"
+required-features = ["std"]
+
+[[test]]
+name = "long_fn_name"
+required-features = ["std"]
+
+[[test]]
+name = "smoke"
+required-features = ["std"]
+edition = '2018'
+
+[[test]]
+name = "accuracy"
+required-features = ["std", "gimli-symbolize"]
+edition = '2018'
+
+[[test]]
+name = "concurrent-panics"
+required-features = ["std"]
+harness = false

library/backtrace/ci/run.sh

@@ -0,0 +1,6 @@
+#!/bin/sh
+
+set -ex
+
+cargo test --target $TARGET
+cargo build --target $TARGET --manifest-path crates/as-if-std/Cargo.toml

library/backtrace/crates/as-if-std/Cargo.toml

@@ -0,0 +1,28 @@
+[package]
+name = "as-if-std"
+version = "0.1.0"
+authors = ["Alex Crichton <alex@alexcrichton.com>"]
+edition = "2018"
+publish = false
+
+[lib]
+test = false
+doc = false
+doctest = false
+bench = false
+
+[dependencies]
+cfg-if = "0.1.10"
+rustc-demangle = "0.1.4"
+libc = { version = "0.2.45", default-features = false }
+addr2line = { version = "0.12.0", default-features = false }
+miniz_oxide = { version = "0.4.0", default-features = false }
+
+[dependencies.object]
+version = "0.20.0"
+default-features = false
+features = ['read_core', 'elf', 'macho', 'pe', 'unaligned']
+
+[features]
+default = ['gimli-symbolize']
+gimli-symbolize = []

library/backtrace/crates/as-if-std/build.rs

@@ -0,0 +1,3 @@
+fn main() {
+    println!("cargo:rustc-cfg=backtrace_in_libstd");
+}

library/backtrace/crates/as-if-std/src/lib.rs

@@ -0,0 +1,21 @@
+// A crate which builds the `backtrace` crate as-if it's included as a
+// submodule into the standard library. We try to set this crate up similarly
+// to the standard library itself to minimize the likelihood of issues when
+// updating the `backtrace` crate.
+
+#![no_std]
+
+extern crate alloc;
+
+// We want to `pub use std::*` in the root but we don't want `std` available in
+// the root namespace, so do this in a funky inner module.
+mod __internal {
+    extern crate std;
+    pub use std::*;
+}
+
+pub use __internal::*;
+
+// This is the magical part which we hope works.
+#[path = "../../../src/lib.rs"]
+mod the_backtrace_crate;

library/backtrace/crates/backtrace-sys/Cargo.toml

@@ -0,0 +1,27 @@
+[package]
+name = "backtrace-sys"
+version = "0.1.37"
+authors = ["Alex Crichton <alex@alexcrichton.com>"]
+build = "build.rs"
+license = "MIT/Apache-2.0"
+repository = "https://github.com/alexcrichton/backtrace-rs"
+homepage = "https://github.com/alexcrichton/backtrace-rs"
+documentation = "http://alexcrichton.com/backtrace-rs"
+description = """
+Bindings to the libbacktrace gcc library
+"""
+
+[dependencies]
+libc = { version = "0.2", default-features = false }
+core = { version = '1.0.0', optional = true, package = 'rustc-std-workspace-core' }
+compiler_builtins = { version = '0.1.2', optional = true }
+
+[build-dependencies]
+cc = "1.0.37"
+
+[features]
+default = ["backtrace-sys"]
+
+# Without this feature, this crate does nothing.
+backtrace-sys = []
+rustc-dep-of-std = ['core', 'compiler_builtins']