mirror of
https://git.proxmox.com/git/rustc
synced 2025-10-13 23:36:24 +00:00
2336 lines
99 KiB
Rust
2336 lines
99 KiB
Rust
use std::collections::VecDeque;
|
|
use std::rc::Rc;
|
|
|
|
use rustc_data_structures::binary_search_util;
|
|
use rustc_data_structures::frozen::Frozen;
|
|
use rustc_data_structures::fx::{FxIndexMap, FxIndexSet};
|
|
use rustc_data_structures::graph::scc::Sccs;
|
|
use rustc_errors::Diagnostic;
|
|
use rustc_hir::def_id::CRATE_DEF_ID;
|
|
use rustc_index::{IndexSlice, IndexVec};
|
|
use rustc_infer::infer::outlives::test_type_match;
|
|
use rustc_infer::infer::region_constraints::{GenericKind, VarInfos, VerifyBound, VerifyIfEq};
|
|
use rustc_infer::infer::{InferCtxt, NllRegionVariableOrigin, RegionVariableOrigin};
|
|
use rustc_middle::mir::{
|
|
BasicBlock, Body, ClosureOutlivesRequirement, ClosureOutlivesSubject, ClosureOutlivesSubjectTy,
|
|
ClosureRegionRequirements, ConstraintCategory, Local, Location, ReturnConstraint,
|
|
TerminatorKind,
|
|
};
|
|
use rustc_middle::traits::ObligationCause;
|
|
use rustc_middle::traits::ObligationCauseCode;
|
|
use rustc_middle::ty::{self, RegionVid, Ty, TyCtxt, TypeFoldable};
|
|
use rustc_mir_dataflow::points::DenseLocationMap;
|
|
use rustc_span::Span;
|
|
|
|
use crate::constraints::graph::{self, NormalConstraintGraph, RegionGraph};
|
|
use crate::dataflow::BorrowIndex;
|
|
use crate::{
|
|
constraints::{ConstraintSccIndex, OutlivesConstraint, OutlivesConstraintSet},
|
|
diagnostics::{RegionErrorKind, RegionErrors, UniverseInfo},
|
|
member_constraints::{MemberConstraintSet, NllMemberConstraintIndex},
|
|
nll::PoloniusOutput,
|
|
region_infer::reverse_sccs::ReverseSccGraph,
|
|
region_infer::values::{
|
|
LivenessValues, PlaceholderIndices, RegionElement, RegionValues, ToElementIndex,
|
|
},
|
|
type_check::{free_region_relations::UniversalRegionRelations, Locations},
|
|
universal_regions::UniversalRegions,
|
|
BorrowckInferCtxt,
|
|
};
|
|
|
|
mod dump_mir;
|
|
mod graphviz;
|
|
mod opaque_types;
|
|
mod reverse_sccs;
|
|
|
|
pub mod values;
|
|
|
|
pub struct RegionInferenceContext<'tcx> {
|
|
pub var_infos: VarInfos,
|
|
|
|
/// Contains the definition for every region variable. Region
|
|
/// variables are identified by their index (`RegionVid`). The
|
|
/// definition contains information about where the region came
|
|
/// from as well as its final inferred value.
|
|
definitions: IndexVec<RegionVid, RegionDefinition<'tcx>>,
|
|
|
|
/// The liveness constraints added to each region. For most
|
|
/// regions, these start out empty and steadily grow, though for
|
|
/// each universally quantified region R they start out containing
|
|
/// the entire CFG and `end(R)`.
|
|
liveness_constraints: LivenessValues,
|
|
|
|
/// The outlives constraints computed by the type-check.
|
|
constraints: Frozen<OutlivesConstraintSet<'tcx>>,
|
|
|
|
/// The constraint-set, but in graph form, making it easy to traverse
|
|
/// the constraints adjacent to a particular region. Used to construct
|
|
/// the SCC (see `constraint_sccs`) and for error reporting.
|
|
constraint_graph: Frozen<NormalConstraintGraph>,
|
|
|
|
/// The SCC computed from `constraints` and the constraint
|
|
/// graph. We have an edge from SCC A to SCC B if `A: B`. Used to
|
|
/// compute the values of each region.
|
|
constraint_sccs: Rc<Sccs<RegionVid, ConstraintSccIndex>>,
|
|
|
|
/// Reverse of the SCC constraint graph -- i.e., an edge `A -> B` exists if
|
|
/// `B: A`. This is used to compute the universal regions that are required
|
|
/// to outlive a given SCC. Computed lazily.
|
|
rev_scc_graph: Option<ReverseSccGraph>,
|
|
|
|
/// The "R0 member of [R1..Rn]" constraints, indexed by SCC.
|
|
member_constraints: Rc<MemberConstraintSet<'tcx, ConstraintSccIndex>>,
|
|
|
|
/// Records the member constraints that we applied to each scc.
|
|
/// This is useful for error reporting. Once constraint
|
|
/// propagation is done, this vector is sorted according to
|
|
/// `member_region_scc`.
|
|
member_constraints_applied: Vec<AppliedMemberConstraint>,
|
|
|
|
/// Map universe indexes to information on why we created it.
|
|
universe_causes: FxIndexMap<ty::UniverseIndex, UniverseInfo<'tcx>>,
|
|
|
|
/// Contains the minimum universe of any variable within the same
|
|
/// SCC. We will ensure that no SCC contains values that are not
|
|
/// visible from this index.
|
|
scc_universes: IndexVec<ConstraintSccIndex, ty::UniverseIndex>,
|
|
|
|
/// Contains a "representative" from each SCC. This will be the
|
|
/// minimal RegionVid belonging to that universe. It is used as a
|
|
/// kind of hacky way to manage checking outlives relationships,
|
|
/// since we can 'canonicalize' each region to the representative
|
|
/// of its SCC and be sure that -- if they have the same repr --
|
|
/// they *must* be equal (though not having the same repr does not
|
|
/// mean they are unequal).
|
|
scc_representatives: IndexVec<ConstraintSccIndex, ty::RegionVid>,
|
|
|
|
/// The final inferred values of the region variables; we compute
|
|
/// one value per SCC. To get the value for any given *region*,
|
|
/// you first find which scc it is a part of.
|
|
scc_values: RegionValues<ConstraintSccIndex>,
|
|
|
|
/// Type constraints that we check after solving.
|
|
type_tests: Vec<TypeTest<'tcx>>,
|
|
|
|
/// Information about the universally quantified regions in scope
|
|
/// on this function.
|
|
universal_regions: Rc<UniversalRegions<'tcx>>,
|
|
|
|
/// Information about how the universally quantified regions in
|
|
/// scope on this function relate to one another.
|
|
universal_region_relations: Frozen<UniversalRegionRelations<'tcx>>,
|
|
}
|
|
|
|
/// Each time that `apply_member_constraint` is successful, it appends
|
|
/// one of these structs to the `member_constraints_applied` field.
|
|
/// This is used in error reporting to trace out what happened.
|
|
///
|
|
/// The way that `apply_member_constraint` works is that it effectively
|
|
/// adds a new lower bound to the SCC it is analyzing: so you wind up
|
|
/// with `'R: 'O` where `'R` is the pick-region and `'O` is the
|
|
/// minimal viable option.
|
|
#[derive(Debug)]
|
|
pub(crate) struct AppliedMemberConstraint {
|
|
/// The SCC that was affected. (The "member region".)
|
|
///
|
|
/// The vector if `AppliedMemberConstraint` elements is kept sorted
|
|
/// by this field.
|
|
pub(crate) member_region_scc: ConstraintSccIndex,
|
|
|
|
/// The "best option" that `apply_member_constraint` found -- this was
|
|
/// added as an "ad-hoc" lower-bound to `member_region_scc`.
|
|
pub(crate) min_choice: ty::RegionVid,
|
|
|
|
/// The "member constraint index" -- we can find out details about
|
|
/// the constraint from
|
|
/// `set.member_constraints[member_constraint_index]`.
|
|
pub(crate) member_constraint_index: NllMemberConstraintIndex,
|
|
}
|
|
|
|
#[derive(Debug)]
|
|
pub(crate) struct RegionDefinition<'tcx> {
|
|
/// What kind of variable is this -- a free region? existential
|
|
/// variable? etc. (See the `NllRegionVariableOrigin` for more
|
|
/// info.)
|
|
pub(crate) origin: NllRegionVariableOrigin,
|
|
|
|
/// Which universe is this region variable defined in? This is
|
|
/// most often `ty::UniverseIndex::ROOT`, but when we encounter
|
|
/// forall-quantifiers like `for<'a> { 'a = 'b }`, we would create
|
|
/// the variable for `'a` in a fresh universe that extends ROOT.
|
|
pub(crate) universe: ty::UniverseIndex,
|
|
|
|
/// If this is 'static or an early-bound region, then this is
|
|
/// `Some(X)` where `X` is the name of the region.
|
|
pub(crate) external_name: Option<ty::Region<'tcx>>,
|
|
}
|
|
|
|
/// N.B., the variants in `Cause` are intentionally ordered. Lower
|
|
/// values are preferred when it comes to error messages. Do not
|
|
/// reorder willy nilly.
|
|
#[derive(Copy, Clone, Debug, PartialOrd, Ord, PartialEq, Eq)]
|
|
pub(crate) enum Cause {
|
|
/// point inserted because Local was live at the given Location
|
|
LiveVar(Local, Location),
|
|
|
|
/// point inserted because Local was dropped at the given Location
|
|
DropVar(Local, Location),
|
|
}
|
|
|
|
/// A "type test" corresponds to an outlives constraint between a type
|
|
/// and a lifetime, like `T: 'x` or `<T as Foo>::Bar: 'x`. They are
|
|
/// translated from the `Verify` region constraints in the ordinary
|
|
/// inference context.
|
|
///
|
|
/// These sorts of constraints are handled differently than ordinary
|
|
/// constraints, at least at present. During type checking, the
|
|
/// `InferCtxt::process_registered_region_obligations` method will
|
|
/// attempt to convert a type test like `T: 'x` into an ordinary
|
|
/// outlives constraint when possible (for example, `&'a T: 'b` will
|
|
/// be converted into `'a: 'b` and registered as a `Constraint`).
|
|
///
|
|
/// In some cases, however, there are outlives relationships that are
|
|
/// not converted into a region constraint, but rather into one of
|
|
/// these "type tests". The distinction is that a type test does not
|
|
/// influence the inference result, but instead just examines the
|
|
/// values that we ultimately inferred for each region variable and
|
|
/// checks that they meet certain extra criteria. If not, an error
|
|
/// can be issued.
|
|
///
|
|
/// One reason for this is that these type tests typically boil down
|
|
/// to a check like `'a: 'x` where `'a` is a universally quantified
|
|
/// region -- and therefore not one whose value is really meant to be
|
|
/// *inferred*, precisely (this is not always the case: one can have a
|
|
/// type test like `<Foo as Trait<'?0>>::Bar: 'x`, where `'?0` is an
|
|
/// inference variable). Another reason is that these type tests can
|
|
/// involve *disjunction* -- that is, they can be satisfied in more
|
|
/// than one way.
|
|
///
|
|
/// For more information about this translation, see
|
|
/// `InferCtxt::process_registered_region_obligations` and
|
|
/// `InferCtxt::type_must_outlive` in `rustc_infer::infer::InferCtxt`.
|
|
#[derive(Clone, Debug)]
|
|
pub struct TypeTest<'tcx> {
|
|
/// The type `T` that must outlive the region.
|
|
pub generic_kind: GenericKind<'tcx>,
|
|
|
|
/// The region `'x` that the type must outlive.
|
|
pub lower_bound: RegionVid,
|
|
|
|
/// The span to blame.
|
|
pub span: Span,
|
|
|
|
/// A test which, if met by the region `'x`, proves that this type
|
|
/// constraint is satisfied.
|
|
pub verify_bound: VerifyBound<'tcx>,
|
|
}
|
|
|
|
/// When we have an unmet lifetime constraint, we try to propagate it outward (e.g. to a closure
|
|
/// environment). If we can't, it is an error.
|
|
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
|
|
enum RegionRelationCheckResult {
|
|
Ok,
|
|
Propagated,
|
|
Error,
|
|
}
|
|
|
|
#[derive(Clone, PartialEq, Eq, Debug)]
|
|
enum Trace<'tcx> {
|
|
StartRegion,
|
|
FromOutlivesConstraint(OutlivesConstraint<'tcx>),
|
|
NotVisited,
|
|
}
|
|
|
|
#[derive(Clone, PartialEq, Eq, Debug)]
|
|
pub enum ExtraConstraintInfo {
|
|
PlaceholderFromPredicate(Span),
|
|
}
|
|
|
|
#[instrument(skip(infcx, sccs), level = "debug")]
|
|
fn sccs_info<'cx, 'tcx>(
|
|
infcx: &'cx BorrowckInferCtxt<'cx, 'tcx>,
|
|
sccs: Rc<Sccs<RegionVid, ConstraintSccIndex>>,
|
|
) {
|
|
use crate::renumber::RegionCtxt;
|
|
|
|
let var_to_origin = infcx.reg_var_to_origin.borrow();
|
|
|
|
let mut var_to_origin_sorted = var_to_origin.clone().into_iter().collect::<Vec<_>>();
|
|
var_to_origin_sorted.sort_by_key(|vto| vto.0);
|
|
|
|
let mut reg_vars_to_origins_str = "region variables to origins:\n".to_string();
|
|
for (reg_var, origin) in var_to_origin_sorted.into_iter() {
|
|
reg_vars_to_origins_str.push_str(&format!("{reg_var:?}: {origin:?}\n"));
|
|
}
|
|
debug!("{}", reg_vars_to_origins_str);
|
|
|
|
let num_components = sccs.scc_data().ranges().len();
|
|
let mut components = vec![FxIndexSet::default(); num_components];
|
|
|
|
for (reg_var_idx, scc_idx) in sccs.scc_indices().iter().enumerate() {
|
|
let reg_var = ty::RegionVid::from_usize(reg_var_idx);
|
|
let origin = var_to_origin.get(®_var).unwrap_or_else(|| &RegionCtxt::Unknown);
|
|
components[scc_idx.as_usize()].insert((reg_var, *origin));
|
|
}
|
|
|
|
let mut components_str = "strongly connected components:".to_string();
|
|
for (scc_idx, reg_vars_origins) in components.iter().enumerate() {
|
|
let regions_info = reg_vars_origins.clone().into_iter().collect::<Vec<_>>();
|
|
components_str.push_str(&format!(
|
|
"{:?}: {:?},\n)",
|
|
ConstraintSccIndex::from_usize(scc_idx),
|
|
regions_info,
|
|
))
|
|
}
|
|
debug!("{}", components_str);
|
|
|
|
// calculate the best representative for each component
|
|
let components_representatives = components
|
|
.into_iter()
|
|
.enumerate()
|
|
.map(|(scc_idx, region_ctxts)| {
|
|
let repr = region_ctxts
|
|
.into_iter()
|
|
.map(|reg_var_origin| reg_var_origin.1)
|
|
.max_by(|x, y| x.preference_value().cmp(&y.preference_value()))
|
|
.unwrap();
|
|
|
|
(ConstraintSccIndex::from_usize(scc_idx), repr)
|
|
})
|
|
.collect::<FxIndexMap<_, _>>();
|
|
|
|
let mut scc_node_to_edges = FxIndexMap::default();
|
|
for (scc_idx, repr) in components_representatives.iter() {
|
|
let edges_range = sccs.scc_data().ranges()[*scc_idx].clone();
|
|
let edges = &sccs.scc_data().all_successors()[edges_range];
|
|
let edge_representatives =
|
|
edges.iter().map(|scc_idx| components_representatives[scc_idx]).collect::<Vec<_>>();
|
|
scc_node_to_edges.insert((scc_idx, repr), edge_representatives);
|
|
}
|
|
|
|
debug!("SCC edges {:#?}", scc_node_to_edges);
|
|
}
|
|
|
|
impl<'tcx> RegionInferenceContext<'tcx> {
|
|
/// Creates a new region inference context with a total of
|
|
/// `num_region_variables` valid inference variables; the first N
|
|
/// of those will be constant regions representing the free
|
|
/// regions defined in `universal_regions`.
|
|
///
|
|
/// The `outlives_constraints` and `type_tests` are an initial set
|
|
/// of constraints produced by the MIR type check.
|
|
pub(crate) fn new<'cx>(
|
|
_infcx: &BorrowckInferCtxt<'cx, 'tcx>,
|
|
var_infos: VarInfos,
|
|
universal_regions: Rc<UniversalRegions<'tcx>>,
|
|
placeholder_indices: Rc<PlaceholderIndices>,
|
|
universal_region_relations: Frozen<UniversalRegionRelations<'tcx>>,
|
|
outlives_constraints: OutlivesConstraintSet<'tcx>,
|
|
member_constraints_in: MemberConstraintSet<'tcx, RegionVid>,
|
|
universe_causes: FxIndexMap<ty::UniverseIndex, UniverseInfo<'tcx>>,
|
|
type_tests: Vec<TypeTest<'tcx>>,
|
|
liveness_constraints: LivenessValues,
|
|
elements: &Rc<DenseLocationMap>,
|
|
) -> Self {
|
|
debug!("universal_regions: {:#?}", universal_regions);
|
|
debug!("outlives constraints: {:#?}", outlives_constraints);
|
|
debug!("placeholder_indices: {:#?}", placeholder_indices);
|
|
debug!("type tests: {:#?}", type_tests);
|
|
|
|
// Create a RegionDefinition for each inference variable.
|
|
let definitions: IndexVec<_, _> = var_infos
|
|
.iter()
|
|
.map(|info| RegionDefinition::new(info.universe, info.origin))
|
|
.collect();
|
|
|
|
let constraints = Frozen::freeze(outlives_constraints);
|
|
let constraint_graph = Frozen::freeze(constraints.graph(definitions.len()));
|
|
let fr_static = universal_regions.fr_static;
|
|
let constraint_sccs = Rc::new(constraints.compute_sccs(&constraint_graph, fr_static));
|
|
|
|
if cfg!(debug_assertions) {
|
|
sccs_info(_infcx, constraint_sccs.clone());
|
|
}
|
|
|
|
let mut scc_values =
|
|
RegionValues::new(elements, universal_regions.len(), &placeholder_indices);
|
|
|
|
for region in liveness_constraints.regions() {
|
|
let scc = constraint_sccs.scc(region);
|
|
scc_values.merge_liveness(scc, region, &liveness_constraints);
|
|
}
|
|
|
|
let scc_universes = Self::compute_scc_universes(&constraint_sccs, &definitions);
|
|
|
|
let scc_representatives = Self::compute_scc_representatives(&constraint_sccs, &definitions);
|
|
|
|
let member_constraints =
|
|
Rc::new(member_constraints_in.into_mapped(|r| constraint_sccs.scc(r)));
|
|
|
|
let mut result = Self {
|
|
var_infos,
|
|
definitions,
|
|
liveness_constraints,
|
|
constraints,
|
|
constraint_graph,
|
|
constraint_sccs,
|
|
rev_scc_graph: None,
|
|
member_constraints,
|
|
member_constraints_applied: Vec::new(),
|
|
universe_causes,
|
|
scc_universes,
|
|
scc_representatives,
|
|
scc_values,
|
|
type_tests,
|
|
universal_regions,
|
|
universal_region_relations,
|
|
};
|
|
|
|
result.init_free_and_bound_regions();
|
|
|
|
result
|
|
}
|
|
|
|
/// Each SCC is the combination of many region variables which
|
|
/// have been equated. Therefore, we can associate a universe with
|
|
/// each SCC which is minimum of all the universes of its
|
|
/// constituent regions -- this is because whatever value the SCC
|
|
/// takes on must be a value that each of the regions within the
|
|
/// SCC could have as well. This implies that the SCC must have
|
|
/// the minimum, or narrowest, universe.
|
|
fn compute_scc_universes(
|
|
constraint_sccs: &Sccs<RegionVid, ConstraintSccIndex>,
|
|
definitions: &IndexSlice<RegionVid, RegionDefinition<'tcx>>,
|
|
) -> IndexVec<ConstraintSccIndex, ty::UniverseIndex> {
|
|
let num_sccs = constraint_sccs.num_sccs();
|
|
let mut scc_universes = IndexVec::from_elem_n(ty::UniverseIndex::MAX, num_sccs);
|
|
|
|
debug!("compute_scc_universes()");
|
|
|
|
// For each region R in universe U, ensure that the universe for the SCC
|
|
// that contains R is "no bigger" than U. This effectively sets the universe
|
|
// for each SCC to be the minimum of the regions within.
|
|
for (region_vid, region_definition) in definitions.iter_enumerated() {
|
|
let scc = constraint_sccs.scc(region_vid);
|
|
let scc_universe = &mut scc_universes[scc];
|
|
let scc_min = std::cmp::min(region_definition.universe, *scc_universe);
|
|
if scc_min != *scc_universe {
|
|
*scc_universe = scc_min;
|
|
debug!(
|
|
"compute_scc_universes: lowered universe of {scc:?} to {scc_min:?} \
|
|
because it contains {region_vid:?} in {region_universe:?}",
|
|
scc = scc,
|
|
scc_min = scc_min,
|
|
region_vid = region_vid,
|
|
region_universe = region_definition.universe,
|
|
);
|
|
}
|
|
}
|
|
|
|
// Walk each SCC `A` and `B` such that `A: B`
|
|
// and ensure that universe(A) can see universe(B).
|
|
//
|
|
// This serves to enforce the 'empty/placeholder' hierarchy
|
|
// (described in more detail on `RegionKind`):
|
|
//
|
|
// ```
|
|
// static -----+
|
|
// | |
|
|
// empty(U0) placeholder(U1)
|
|
// | /
|
|
// empty(U1)
|
|
// ```
|
|
//
|
|
// In particular, imagine we have variables R0 in U0 and R1
|
|
// created in U1, and constraints like this;
|
|
//
|
|
// ```
|
|
// R1: !1 // R1 outlives the placeholder in U1
|
|
// R1: R0 // R1 outlives R0
|
|
// ```
|
|
//
|
|
// Here, we wish for R1 to be `'static`, because it
|
|
// cannot outlive `placeholder(U1)` and `empty(U0)` any other way.
|
|
//
|
|
// Thanks to this loop, what happens is that the `R1: R0`
|
|
// constraint lowers the universe of `R1` to `U0`, which in turn
|
|
// means that the `R1: !1` constraint will (later) cause
|
|
// `R1` to become `'static`.
|
|
for scc_a in constraint_sccs.all_sccs() {
|
|
for &scc_b in constraint_sccs.successors(scc_a) {
|
|
let scc_universe_a = scc_universes[scc_a];
|
|
let scc_universe_b = scc_universes[scc_b];
|
|
let scc_universe_min = std::cmp::min(scc_universe_a, scc_universe_b);
|
|
if scc_universe_a != scc_universe_min {
|
|
scc_universes[scc_a] = scc_universe_min;
|
|
|
|
debug!(
|
|
"compute_scc_universes: lowered universe of {scc_a:?} to {scc_universe_min:?} \
|
|
because {scc_a:?}: {scc_b:?} and {scc_b:?} is in universe {scc_universe_b:?}",
|
|
scc_a = scc_a,
|
|
scc_b = scc_b,
|
|
scc_universe_min = scc_universe_min,
|
|
scc_universe_b = scc_universe_b
|
|
);
|
|
}
|
|
}
|
|
}
|
|
|
|
debug!("compute_scc_universes: scc_universe = {:#?}", scc_universes);
|
|
|
|
scc_universes
|
|
}
|
|
|
|
/// For each SCC, we compute a unique `RegionVid` (in fact, the
|
|
/// minimal one that belongs to the SCC). See
|
|
/// `scc_representatives` field of `RegionInferenceContext` for
|
|
/// more details.
|
|
fn compute_scc_representatives(
|
|
constraints_scc: &Sccs<RegionVid, ConstraintSccIndex>,
|
|
definitions: &IndexSlice<RegionVid, RegionDefinition<'tcx>>,
|
|
) -> IndexVec<ConstraintSccIndex, ty::RegionVid> {
|
|
let num_sccs = constraints_scc.num_sccs();
|
|
let next_region_vid = definitions.next_index();
|
|
let mut scc_representatives = IndexVec::from_elem_n(next_region_vid, num_sccs);
|
|
|
|
for region_vid in definitions.indices() {
|
|
let scc = constraints_scc.scc(region_vid);
|
|
let prev_min = scc_representatives[scc];
|
|
scc_representatives[scc] = region_vid.min(prev_min);
|
|
}
|
|
|
|
scc_representatives
|
|
}
|
|
|
|
/// Initializes the region variables for each universally
|
|
/// quantified region (lifetime parameter). The first N variables
|
|
/// always correspond to the regions appearing in the function
|
|
/// signature (both named and anonymous) and where-clauses. This
|
|
/// function iterates over those regions and initializes them with
|
|
/// minimum values.
|
|
///
|
|
/// For example:
|
|
/// ```
|
|
/// fn foo<'a, 'b>( /* ... */ ) where 'a: 'b { /* ... */ }
|
|
/// ```
|
|
/// would initialize two variables like so:
|
|
/// ```ignore (illustrative)
|
|
/// R0 = { CFG, R0 } // 'a
|
|
/// R1 = { CFG, R0, R1 } // 'b
|
|
/// ```
|
|
/// Here, R0 represents `'a`, and it contains (a) the entire CFG
|
|
/// and (b) any universally quantified regions that it outlives,
|
|
/// which in this case is just itself. R1 (`'b`) in contrast also
|
|
/// outlives `'a` and hence contains R0 and R1.
|
|
fn init_free_and_bound_regions(&mut self) {
|
|
// Update the names (if any)
|
|
// This iterator has unstable order but we collect it all into an IndexVec
|
|
for (external_name, variable) in self.universal_regions.named_universal_regions() {
|
|
debug!(
|
|
"init_universal_regions: region {:?} has external name {:?}",
|
|
variable, external_name
|
|
);
|
|
self.definitions[variable].external_name = Some(external_name);
|
|
}
|
|
|
|
for variable in self.definitions.indices() {
|
|
let scc = self.constraint_sccs.scc(variable);
|
|
|
|
match self.definitions[variable].origin {
|
|
NllRegionVariableOrigin::FreeRegion => {
|
|
// For each free, universally quantified region X:
|
|
|
|
// Add all nodes in the CFG to liveness constraints
|
|
self.liveness_constraints.add_all_points(variable);
|
|
self.scc_values.add_all_points(scc);
|
|
|
|
// Add `end(X)` into the set for X.
|
|
self.scc_values.add_element(scc, variable);
|
|
}
|
|
|
|
NllRegionVariableOrigin::Placeholder(placeholder) => {
|
|
// Each placeholder region is only visible from
|
|
// its universe `ui` and its extensions. So we
|
|
// can't just add it into `scc` unless the
|
|
// universe of the scc can name this region.
|
|
let scc_universe = self.scc_universes[scc];
|
|
if scc_universe.can_name(placeholder.universe) {
|
|
self.scc_values.add_element(scc, placeholder);
|
|
} else {
|
|
debug!(
|
|
"init_free_and_bound_regions: placeholder {:?} is \
|
|
not compatible with universe {:?} of its SCC {:?}",
|
|
placeholder, scc_universe, scc,
|
|
);
|
|
self.add_incompatible_universe(scc);
|
|
}
|
|
}
|
|
|
|
NllRegionVariableOrigin::Existential { .. } => {
|
|
// For existential, regions, nothing to do.
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
/// Returns an iterator over all the region indices.
|
|
pub fn regions(&self) -> impl Iterator<Item = RegionVid> + 'tcx {
|
|
self.definitions.indices()
|
|
}
|
|
|
|
/// Given a universal region in scope on the MIR, returns the
|
|
/// corresponding index.
|
|
///
|
|
/// (Panics if `r` is not a registered universal region.)
|
|
pub fn to_region_vid(&self, r: ty::Region<'tcx>) -> RegionVid {
|
|
self.universal_regions.to_region_vid(r)
|
|
}
|
|
|
|
/// Returns an iterator over all the outlives constraints.
|
|
pub fn outlives_constraints(&self) -> impl Iterator<Item = OutlivesConstraint<'tcx>> + '_ {
|
|
self.constraints.outlives().iter().copied()
|
|
}
|
|
|
|
/// Adds annotations for `#[rustc_regions]`; see `UniversalRegions::annotate`.
|
|
pub(crate) fn annotate(&self, tcx: TyCtxt<'tcx>, err: &mut Diagnostic) {
|
|
self.universal_regions.annotate(tcx, err)
|
|
}
|
|
|
|
/// Returns `true` if the region `r` contains the point `p`.
|
|
///
|
|
/// Panics if called before `solve()` executes,
|
|
pub(crate) fn region_contains(&self, r: RegionVid, p: impl ToElementIndex) -> bool {
|
|
let scc = self.constraint_sccs.scc(r);
|
|
self.scc_values.contains(scc, p)
|
|
}
|
|
|
|
/// Returns the lowest statement index in `start..=end` which is not contained by `r`.
|
|
///
|
|
/// Panics if called before `solve()` executes.
|
|
pub(crate) fn first_non_contained_inclusive(
|
|
&self,
|
|
r: RegionVid,
|
|
block: BasicBlock,
|
|
start: usize,
|
|
end: usize,
|
|
) -> Option<usize> {
|
|
let scc = self.constraint_sccs.scc(r);
|
|
self.scc_values.first_non_contained_inclusive(scc, block, start, end)
|
|
}
|
|
|
|
/// Returns access to the value of `r` for debugging purposes.
|
|
pub(crate) fn region_value_str(&self, r: RegionVid) -> String {
|
|
let scc = self.constraint_sccs.scc(r);
|
|
self.scc_values.region_value_str(scc)
|
|
}
|
|
|
|
pub(crate) fn placeholders_contained_in<'a>(
|
|
&'a self,
|
|
r: RegionVid,
|
|
) -> impl Iterator<Item = ty::PlaceholderRegion> + 'a {
|
|
let scc = self.constraint_sccs.scc(r);
|
|
self.scc_values.placeholders_contained_in(scc)
|
|
}
|
|
|
|
/// Returns access to the value of `r` for debugging purposes.
|
|
pub(crate) fn region_universe(&self, r: RegionVid) -> ty::UniverseIndex {
|
|
let scc = self.constraint_sccs.scc(r);
|
|
self.scc_universes[scc]
|
|
}
|
|
|
|
/// Once region solving has completed, this function will return the member constraints that
|
|
/// were applied to the value of a given SCC `scc`. See `AppliedMemberConstraint`.
|
|
pub(crate) fn applied_member_constraints(
|
|
&self,
|
|
scc: ConstraintSccIndex,
|
|
) -> &[AppliedMemberConstraint] {
|
|
binary_search_util::binary_search_slice(
|
|
&self.member_constraints_applied,
|
|
|applied| applied.member_region_scc,
|
|
&scc,
|
|
)
|
|
}
|
|
|
|
/// Performs region inference and report errors if we see any
|
|
/// unsatisfiable constraints. If this is a closure, returns the
|
|
/// region requirements to propagate to our creator, if any.
|
|
#[instrument(skip(self, infcx, body, polonius_output), level = "debug")]
|
|
pub(super) fn solve(
|
|
&mut self,
|
|
infcx: &InferCtxt<'tcx>,
|
|
param_env: ty::ParamEnv<'tcx>,
|
|
body: &Body<'tcx>,
|
|
polonius_output: Option<Rc<PoloniusOutput>>,
|
|
) -> (Option<ClosureRegionRequirements<'tcx>>, RegionErrors<'tcx>) {
|
|
let mir_def_id = body.source.def_id();
|
|
self.propagate_constraints(body);
|
|
|
|
let mut errors_buffer = RegionErrors::new(infcx.tcx);
|
|
|
|
// If this is a closure, we can propagate unsatisfied
|
|
// `outlives_requirements` to our creator, so create a vector
|
|
// to store those. Otherwise, we'll pass in `None` to the
|
|
// functions below, which will trigger them to report errors
|
|
// eagerly.
|
|
let mut outlives_requirements = infcx.tcx.is_typeck_child(mir_def_id).then(Vec::new);
|
|
|
|
self.check_type_tests(infcx, body, outlives_requirements.as_mut(), &mut errors_buffer);
|
|
|
|
debug!(?errors_buffer);
|
|
debug!(?outlives_requirements);
|
|
|
|
// In Polonius mode, the errors about missing universal region relations are in the output
|
|
// and need to be emitted or propagated. Otherwise, we need to check whether the
|
|
// constraints were too strong, and if so, emit or propagate those errors.
|
|
if infcx.tcx.sess.opts.unstable_opts.polonius.is_legacy_enabled() {
|
|
self.check_polonius_subset_errors(
|
|
outlives_requirements.as_mut(),
|
|
&mut errors_buffer,
|
|
polonius_output.expect("Polonius output is unavailable despite `-Z polonius`"),
|
|
);
|
|
} else {
|
|
self.check_universal_regions(outlives_requirements.as_mut(), &mut errors_buffer);
|
|
}
|
|
|
|
debug!(?errors_buffer);
|
|
|
|
if errors_buffer.is_empty() {
|
|
self.check_member_constraints(infcx, &mut errors_buffer);
|
|
}
|
|
|
|
debug!(?errors_buffer);
|
|
|
|
let outlives_requirements = outlives_requirements.unwrap_or_default();
|
|
|
|
if outlives_requirements.is_empty() {
|
|
(None, errors_buffer)
|
|
} else {
|
|
let num_external_vids = self.universal_regions.num_global_and_external_regions();
|
|
(
|
|
Some(ClosureRegionRequirements { num_external_vids, outlives_requirements }),
|
|
errors_buffer,
|
|
)
|
|
}
|
|
}
|
|
|
|
/// Propagate the region constraints: this will grow the values
|
|
/// for each region variable until all the constraints are
|
|
/// satisfied. Note that some values may grow **too** large to be
|
|
/// feasible, but we check this later.
|
|
#[instrument(skip(self, _body), level = "debug")]
|
|
fn propagate_constraints(&mut self, _body: &Body<'tcx>) {
|
|
debug!("constraints={:#?}", {
|
|
let mut constraints: Vec<_> = self.outlives_constraints().collect();
|
|
constraints.sort_by_key(|c| (c.sup, c.sub));
|
|
constraints
|
|
.into_iter()
|
|
.map(|c| (c, self.constraint_sccs.scc(c.sup), self.constraint_sccs.scc(c.sub)))
|
|
.collect::<Vec<_>>()
|
|
});
|
|
|
|
// To propagate constraints, we walk the DAG induced by the
|
|
// SCC. For each SCC, we visit its successors and compute
|
|
// their values, then we union all those values to get our
|
|
// own.
|
|
let constraint_sccs = self.constraint_sccs.clone();
|
|
for scc in constraint_sccs.all_sccs() {
|
|
self.compute_value_for_scc(scc);
|
|
}
|
|
|
|
// Sort the applied member constraints so we can binary search
|
|
// through them later.
|
|
self.member_constraints_applied.sort_by_key(|applied| applied.member_region_scc);
|
|
}
|
|
|
|
/// Computes the value of the SCC `scc_a`, which has not yet been
|
|
/// computed, by unioning the values of its successors.
|
|
/// Assumes that all successors have been computed already
|
|
/// (which is assured by iterating over SCCs in dependency order).
|
|
#[instrument(skip(self), level = "debug")]
|
|
fn compute_value_for_scc(&mut self, scc_a: ConstraintSccIndex) {
|
|
let constraint_sccs = self.constraint_sccs.clone();
|
|
|
|
// Walk each SCC `B` such that `A: B`...
|
|
for &scc_b in constraint_sccs.successors(scc_a) {
|
|
debug!(?scc_b);
|
|
|
|
// ...and add elements from `B` into `A`. One complication
|
|
// arises because of universes: If `B` contains something
|
|
// that `A` cannot name, then `A` can only contain `B` if
|
|
// it outlives static.
|
|
if self.universe_compatible(scc_b, scc_a) {
|
|
// `A` can name everything that is in `B`, so just
|
|
// merge the bits.
|
|
self.scc_values.add_region(scc_a, scc_b);
|
|
} else {
|
|
self.add_incompatible_universe(scc_a);
|
|
}
|
|
}
|
|
|
|
// Now take member constraints into account.
|
|
let member_constraints = self.member_constraints.clone();
|
|
for m_c_i in member_constraints.indices(scc_a) {
|
|
self.apply_member_constraint(scc_a, m_c_i, member_constraints.choice_regions(m_c_i));
|
|
}
|
|
|
|
debug!(value = ?self.scc_values.region_value_str(scc_a));
|
|
}
|
|
|
|
/// Invoked for each `R0 member of [R1..Rn]` constraint.
|
|
///
|
|
/// `scc` is the SCC containing R0, and `choice_regions` are the
|
|
/// `R1..Rn` regions -- they are always known to be universal
|
|
/// regions (and if that's not true, we just don't attempt to
|
|
/// enforce the constraint).
|
|
///
|
|
/// The current value of `scc` at the time the method is invoked
|
|
/// is considered a *lower bound*. If possible, we will modify
|
|
/// the constraint to set it equal to one of the option regions.
|
|
/// If we make any changes, returns true, else false.
|
|
///
|
|
/// This function only adds the member constraints to the region graph,
|
|
/// it does not check them. They are later checked in
|
|
/// `check_member_constraints` after the region graph has been computed.
|
|
#[instrument(skip(self, member_constraint_index), level = "debug")]
|
|
fn apply_member_constraint(
|
|
&mut self,
|
|
scc: ConstraintSccIndex,
|
|
member_constraint_index: NllMemberConstraintIndex,
|
|
choice_regions: &[ty::RegionVid],
|
|
) {
|
|
// Lazily compute the reverse graph, we'll need it later.
|
|
self.compute_reverse_scc_graph();
|
|
|
|
// Create a mutable vector of the options. We'll try to winnow
|
|
// them down.
|
|
let mut choice_regions: Vec<ty::RegionVid> = choice_regions.to_vec();
|
|
|
|
// Convert to the SCC representative: sometimes we have inference
|
|
// variables in the member constraint that wind up equated with
|
|
// universal regions. The scc representative is the minimal numbered
|
|
// one from the corresponding scc so it will be the universal region
|
|
// if one exists.
|
|
for c_r in &mut choice_regions {
|
|
let scc = self.constraint_sccs.scc(*c_r);
|
|
*c_r = self.scc_representatives[scc];
|
|
}
|
|
|
|
// If the member region lives in a higher universe, we currently choose
|
|
// the most conservative option by leaving it unchanged.
|
|
if self.scc_universes[scc] != ty::UniverseIndex::ROOT {
|
|
return;
|
|
}
|
|
debug_assert!(
|
|
self.scc_values.placeholders_contained_in(scc).next().is_none(),
|
|
"scc {:?} in a member constraint has placeholder value: {:?}",
|
|
scc,
|
|
self.scc_values.region_value_str(scc),
|
|
);
|
|
|
|
// The existing value for `scc` is a lower-bound. This will
|
|
// consist of some set `{P} + {LB}` of points `{P}` and
|
|
// lower-bound free regions `{LB}`. As each choice region `O`
|
|
// is a free region, it will outlive the points. But we can
|
|
// only consider the option `O` if `O: LB`.
|
|
choice_regions.retain(|&o_r| {
|
|
self.scc_values
|
|
.universal_regions_outlived_by(scc)
|
|
.all(|lb| self.universal_region_relations.outlives(o_r, lb))
|
|
});
|
|
debug!(?choice_regions, "after lb");
|
|
|
|
// Now find all the *upper bounds* -- that is, each UB is a
|
|
// free region that must outlive the member region `R0` (`UB:
|
|
// R0`). Therefore, we need only keep an option `O` if `UB: O`
|
|
// for all UB.
|
|
let universal_region_relations = &self.universal_region_relations;
|
|
for ub in self.rev_scc_graph.as_ref().unwrap().upper_bounds(scc) {
|
|
debug!(?ub);
|
|
choice_regions.retain(|&o_r| universal_region_relations.outlives(ub, o_r));
|
|
}
|
|
debug!(?choice_regions, "after ub");
|
|
|
|
// At this point we can pick any member of `choice_regions`, but to avoid potential
|
|
// non-determinism we will pick the *unique minimum* choice.
|
|
//
|
|
// Because universal regions are only partially ordered (i.e, not every two regions are
|
|
// comparable), we will ignore any region that doesn't compare to all others when picking
|
|
// the minimum choice.
|
|
// For example, consider `choice_regions = ['static, 'a, 'b, 'c, 'd, 'e]`, where
|
|
// `'static: 'a, 'static: 'b, 'a: 'c, 'b: 'c, 'c: 'd, 'c: 'e`.
|
|
// `['d, 'e]` are ignored because they do not compare - the same goes for `['a, 'b]`.
|
|
let totally_ordered_subset = choice_regions.iter().copied().filter(|&r1| {
|
|
choice_regions.iter().all(|&r2| {
|
|
self.universal_region_relations.outlives(r1, r2)
|
|
|| self.universal_region_relations.outlives(r2, r1)
|
|
})
|
|
});
|
|
// Now we're left with `['static, 'c]`. Pick `'c` as the minimum!
|
|
let Some(min_choice) = totally_ordered_subset.reduce(|r1, r2| {
|
|
let r1_outlives_r2 = self.universal_region_relations.outlives(r1, r2);
|
|
let r2_outlives_r1 = self.universal_region_relations.outlives(r2, r1);
|
|
match (r1_outlives_r2, r2_outlives_r1) {
|
|
(true, true) => r1.min(r2),
|
|
(true, false) => r2,
|
|
(false, true) => r1,
|
|
(false, false) => bug!("incomparable regions in total order"),
|
|
}
|
|
}) else {
|
|
debug!("no unique minimum choice");
|
|
return;
|
|
};
|
|
|
|
let min_choice_scc = self.constraint_sccs.scc(min_choice);
|
|
debug!(?min_choice, ?min_choice_scc);
|
|
if self.scc_values.add_region(scc, min_choice_scc) {
|
|
self.member_constraints_applied.push(AppliedMemberConstraint {
|
|
member_region_scc: scc,
|
|
min_choice,
|
|
member_constraint_index,
|
|
});
|
|
}
|
|
}
|
|
|
|
/// Returns `true` if all the elements in the value of `scc_b` are nameable
|
|
/// in `scc_a`. Used during constraint propagation, and only once
|
|
/// the value of `scc_b` has been computed.
|
|
fn universe_compatible(&self, scc_b: ConstraintSccIndex, scc_a: ConstraintSccIndex) -> bool {
|
|
let universe_a = self.scc_universes[scc_a];
|
|
|
|
// Quick check: if scc_b's declared universe is a subset of
|
|
// scc_a's declared universe (typically, both are ROOT), then
|
|
// it cannot contain any problematic universe elements.
|
|
if universe_a.can_name(self.scc_universes[scc_b]) {
|
|
return true;
|
|
}
|
|
|
|
// Otherwise, we have to iterate over the universe elements in
|
|
// B's value, and check whether all of them are nameable
|
|
// from universe_a
|
|
self.scc_values.placeholders_contained_in(scc_b).all(|p| universe_a.can_name(p.universe))
|
|
}
|
|
|
|
/// Extend `scc` so that it can outlive some placeholder region
|
|
/// from a universe it can't name; at present, the only way for
|
|
/// this to be true is if `scc` outlives `'static`. This is
|
|
/// actually stricter than necessary: ideally, we'd support bounds
|
|
/// like `for<'a: 'b>` that might then allow us to approximate
|
|
/// `'a` with `'b` and not `'static`. But it will have to do for
|
|
/// now.
|
|
fn add_incompatible_universe(&mut self, scc: ConstraintSccIndex) {
|
|
debug!("add_incompatible_universe(scc={:?})", scc);
|
|
|
|
let fr_static = self.universal_regions.fr_static;
|
|
self.scc_values.add_all_points(scc);
|
|
self.scc_values.add_element(scc, fr_static);
|
|
}
|
|
|
|
/// Once regions have been propagated, this method is used to see
|
|
/// whether the "type tests" produced by typeck were satisfied;
|
|
/// type tests encode type-outlives relationships like `T:
|
|
/// 'a`. See `TypeTest` for more details.
|
|
fn check_type_tests(
|
|
&self,
|
|
infcx: &InferCtxt<'tcx>,
|
|
body: &Body<'tcx>,
|
|
mut propagated_outlives_requirements: Option<&mut Vec<ClosureOutlivesRequirement<'tcx>>>,
|
|
errors_buffer: &mut RegionErrors<'tcx>,
|
|
) {
|
|
let tcx = infcx.tcx;
|
|
|
|
// Sometimes we register equivalent type-tests that would
|
|
// result in basically the exact same error being reported to
|
|
// the user. Avoid that.
|
|
let mut deduplicate_errors = FxIndexSet::default();
|
|
|
|
for type_test in &self.type_tests {
|
|
debug!("check_type_test: {:?}", type_test);
|
|
|
|
let generic_ty = type_test.generic_kind.to_ty(tcx);
|
|
if self.eval_verify_bound(
|
|
infcx,
|
|
generic_ty,
|
|
type_test.lower_bound,
|
|
&type_test.verify_bound,
|
|
) {
|
|
continue;
|
|
}
|
|
|
|
if let Some(propagated_outlives_requirements) = &mut propagated_outlives_requirements {
|
|
if self.try_promote_type_test(
|
|
infcx,
|
|
body,
|
|
type_test,
|
|
propagated_outlives_requirements,
|
|
) {
|
|
continue;
|
|
}
|
|
}
|
|
|
|
// Type-test failed. Report the error.
|
|
let erased_generic_kind = infcx.tcx.erase_regions(type_test.generic_kind);
|
|
|
|
// Skip duplicate-ish errors.
|
|
if deduplicate_errors.insert((
|
|
erased_generic_kind,
|
|
type_test.lower_bound,
|
|
type_test.span,
|
|
)) {
|
|
debug!(
|
|
"check_type_test: reporting error for erased_generic_kind={:?}, \
|
|
lower_bound_region={:?}, \
|
|
type_test.span={:?}",
|
|
erased_generic_kind, type_test.lower_bound, type_test.span,
|
|
);
|
|
|
|
errors_buffer.push(RegionErrorKind::TypeTestError { type_test: type_test.clone() });
|
|
}
|
|
}
|
|
}
|
|
|
|
/// Invoked when we have some type-test (e.g., `T: 'X`) that we cannot
|
|
/// prove to be satisfied. If this is a closure, we will attempt to
|
|
/// "promote" this type-test into our `ClosureRegionRequirements` and
|
|
/// hence pass it up the creator. To do this, we have to phrase the
|
|
/// type-test in terms of external free regions, as local free
|
|
/// regions are not nameable by the closure's creator.
|
|
///
|
|
/// Promotion works as follows: we first check that the type `T`
|
|
/// contains only regions that the creator knows about. If this is
|
|
/// true, then -- as a consequence -- we know that all regions in
|
|
/// the type `T` are free regions that outlive the closure body. If
|
|
/// false, then promotion fails.
|
|
///
|
|
/// Once we've promoted T, we have to "promote" `'X` to some region
|
|
/// that is "external" to the closure. Generally speaking, a region
|
|
/// may be the union of some points in the closure body as well as
|
|
/// various free lifetimes. We can ignore the points in the closure
|
|
/// body: if the type T can be expressed in terms of external regions,
|
|
/// we know it outlives the points in the closure body. That
|
|
/// just leaves the free regions.
|
|
///
|
|
/// The idea then is to lower the `T: 'X` constraint into multiple
|
|
/// bounds -- e.g., if `'X` is the union of two free lifetimes,
|
|
/// `'1` and `'2`, then we would create `T: '1` and `T: '2`.
|
|
#[instrument(level = "debug", skip(self, infcx, propagated_outlives_requirements))]
|
|
fn try_promote_type_test(
|
|
&self,
|
|
infcx: &InferCtxt<'tcx>,
|
|
body: &Body<'tcx>,
|
|
type_test: &TypeTest<'tcx>,
|
|
propagated_outlives_requirements: &mut Vec<ClosureOutlivesRequirement<'tcx>>,
|
|
) -> bool {
|
|
let tcx = infcx.tcx;
|
|
|
|
let TypeTest { generic_kind, lower_bound, span: _, verify_bound: _ } = type_test;
|
|
|
|
let generic_ty = generic_kind.to_ty(tcx);
|
|
let Some(subject) = self.try_promote_type_test_subject(infcx, generic_ty) else {
|
|
return false;
|
|
};
|
|
|
|
debug!("subject = {:?}", subject);
|
|
|
|
let r_scc = self.constraint_sccs.scc(*lower_bound);
|
|
|
|
debug!(
|
|
"lower_bound = {:?} r_scc={:?} universe={:?}",
|
|
lower_bound, r_scc, self.scc_universes[r_scc]
|
|
);
|
|
|
|
// If the type test requires that `T: 'a` where `'a` is a
|
|
// placeholder from another universe, that effectively requires
|
|
// `T: 'static`, so we have to propagate that requirement.
|
|
//
|
|
// It doesn't matter *what* universe because the promoted `T` will
|
|
// always be in the root universe.
|
|
if let Some(p) = self.scc_values.placeholders_contained_in(r_scc).next() {
|
|
debug!("encountered placeholder in higher universe: {:?}, requiring 'static", p);
|
|
let static_r = self.universal_regions.fr_static;
|
|
propagated_outlives_requirements.push(ClosureOutlivesRequirement {
|
|
subject,
|
|
outlived_free_region: static_r,
|
|
blame_span: type_test.span,
|
|
category: ConstraintCategory::Boring,
|
|
});
|
|
|
|
// we can return here -- the code below might push add'l constraints
|
|
// but they would all be weaker than this one.
|
|
return true;
|
|
}
|
|
|
|
// For each region outlived by lower_bound find a non-local,
|
|
// universal region (it may be the same region) and add it to
|
|
// `ClosureOutlivesRequirement`.
|
|
for ur in self.scc_values.universal_regions_outlived_by(r_scc) {
|
|
debug!("universal_region_outlived_by ur={:?}", ur);
|
|
// Check whether we can already prove that the "subject" outlives `ur`.
|
|
// If so, we don't have to propagate this requirement to our caller.
|
|
//
|
|
// To continue the example from the function, if we are trying to promote
|
|
// a requirement that `T: 'X`, and we know that `'X = '1 + '2` (i.e., the union
|
|
// `'1` and `'2`), then in this loop `ur` will be `'1` (and `'2`). So here
|
|
// we check whether `T: '1` is something we *can* prove. If so, no need
|
|
// to propagate that requirement.
|
|
//
|
|
// This is needed because -- particularly in the case
|
|
// where `ur` is a local bound -- we are sometimes in a
|
|
// position to prove things that our caller cannot. See
|
|
// #53570 for an example.
|
|
if self.eval_verify_bound(infcx, generic_ty, ur, &type_test.verify_bound) {
|
|
continue;
|
|
}
|
|
|
|
let non_local_ub = self.universal_region_relations.non_local_upper_bounds(ur);
|
|
debug!("try_promote_type_test: non_local_ub={:?}", non_local_ub);
|
|
|
|
// This is slightly too conservative. To show T: '1, given `'2: '1`
|
|
// and `'3: '1` we only need to prove that T: '2 *or* T: '3, but to
|
|
// avoid potential non-determinism we approximate this by requiring
|
|
// T: '1 and T: '2.
|
|
for upper_bound in non_local_ub {
|
|
debug_assert!(self.universal_regions.is_universal_region(upper_bound));
|
|
debug_assert!(!self.universal_regions.is_local_free_region(upper_bound));
|
|
|
|
let requirement = ClosureOutlivesRequirement {
|
|
subject,
|
|
outlived_free_region: upper_bound,
|
|
blame_span: type_test.span,
|
|
category: ConstraintCategory::Boring,
|
|
};
|
|
debug!("try_promote_type_test: pushing {:#?}", requirement);
|
|
propagated_outlives_requirements.push(requirement);
|
|
}
|
|
}
|
|
true
|
|
}
|
|
|
|
/// When we promote a type test `T: 'r`, we have to replace all region
|
|
/// variables in the type `T` with an equal universal region from the
|
|
/// closure signature.
|
|
/// This is not always possible, so this is a fallible process.
|
|
#[instrument(level = "debug", skip(self, infcx))]
|
|
fn try_promote_type_test_subject(
|
|
&self,
|
|
infcx: &InferCtxt<'tcx>,
|
|
ty: Ty<'tcx>,
|
|
) -> Option<ClosureOutlivesSubject<'tcx>> {
|
|
let tcx = infcx.tcx;
|
|
|
|
// Opaque types' args may include useless lifetimes.
|
|
// We will replace them with ReStatic.
|
|
struct OpaqueFolder<'tcx> {
|
|
tcx: TyCtxt<'tcx>,
|
|
}
|
|
impl<'tcx> ty::TypeFolder<TyCtxt<'tcx>> for OpaqueFolder<'tcx> {
|
|
fn interner(&self) -> TyCtxt<'tcx> {
|
|
self.tcx
|
|
}
|
|
fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
|
|
use ty::TypeSuperFoldable as _;
|
|
let tcx = self.tcx;
|
|
let &ty::Alias(ty::Opaque, ty::AliasTy { args, def_id, .. }) = t.kind() else {
|
|
return t.super_fold_with(self);
|
|
};
|
|
let args = std::iter::zip(args, tcx.variances_of(def_id)).map(|(arg, v)| {
|
|
match (arg.unpack(), v) {
|
|
(ty::GenericArgKind::Lifetime(_), ty::Bivariant) => {
|
|
tcx.lifetimes.re_static.into()
|
|
}
|
|
_ => arg.fold_with(self),
|
|
}
|
|
});
|
|
Ty::new_opaque(tcx, def_id, tcx.mk_args_from_iter(args))
|
|
}
|
|
}
|
|
|
|
let ty = ty.fold_with(&mut OpaqueFolder { tcx });
|
|
let mut failed = false;
|
|
|
|
let ty = tcx.fold_regions(ty, |r, _depth| {
|
|
let r_vid = self.to_region_vid(r);
|
|
let r_scc = self.constraint_sccs.scc(r_vid);
|
|
|
|
// The challenge is this. We have some region variable `r`
|
|
// whose value is a set of CFG points and universal
|
|
// regions. We want to find if that set is *equivalent* to
|
|
// any of the named regions found in the closure.
|
|
// To do so, we simply check every candidate `u_r` for equality.
|
|
self.scc_values
|
|
.universal_regions_outlived_by(r_scc)
|
|
.filter(|&u_r| !self.universal_regions.is_local_free_region(u_r))
|
|
.find(|&u_r| self.eval_equal(u_r, r_vid))
|
|
.map(|u_r| ty::Region::new_var(tcx, u_r))
|
|
// In case we could not find a named region to map to,
|
|
// we will return `None` below.
|
|
.unwrap_or_else(|| {
|
|
failed = true;
|
|
r
|
|
})
|
|
});
|
|
|
|
debug!("try_promote_type_test_subject: folded ty = {:?}", ty);
|
|
|
|
// This will be true if we failed to promote some region.
|
|
if failed {
|
|
return None;
|
|
}
|
|
|
|
Some(ClosureOutlivesSubject::Ty(ClosureOutlivesSubjectTy::bind(tcx, ty)))
|
|
}
|
|
|
|
/// Returns a universally quantified region that outlives the
|
|
/// value of `r` (`r` may be existentially or universally
|
|
/// quantified).
|
|
///
|
|
/// Since `r` is (potentially) an existential region, it has some
|
|
/// value which may include (a) any number of points in the CFG
|
|
/// and (b) any number of `end('x)` elements of universally
|
|
/// quantified regions. To convert this into a single universal
|
|
/// region we do as follows:
|
|
///
|
|
/// - Ignore the CFG points in `'r`. All universally quantified regions
|
|
/// include the CFG anyhow.
|
|
/// - For each `end('x)` element in `'r`, compute the mutual LUB, yielding
|
|
/// a result `'y`.
|
|
#[instrument(skip(self), level = "debug", ret)]
|
|
pub(crate) fn universal_upper_bound(&self, r: RegionVid) -> RegionVid {
|
|
debug!(r = %self.region_value_str(r));
|
|
|
|
// Find the smallest universal region that contains all other
|
|
// universal regions within `region`.
|
|
let mut lub = self.universal_regions.fr_fn_body;
|
|
let r_scc = self.constraint_sccs.scc(r);
|
|
for ur in self.scc_values.universal_regions_outlived_by(r_scc) {
|
|
lub = self.universal_region_relations.postdom_upper_bound(lub, ur);
|
|
}
|
|
|
|
lub
|
|
}
|
|
|
|
/// Like `universal_upper_bound`, but returns an approximation more suitable
|
|
/// for diagnostics. If `r` contains multiple disjoint universal regions
|
|
/// (e.g. 'a and 'b in `fn foo<'a, 'b> { ... }`, we pick the lower-numbered region.
|
|
/// This corresponds to picking named regions over unnamed regions
|
|
/// (e.g. picking early-bound regions over a closure late-bound region).
|
|
///
|
|
/// This means that the returned value may not be a true upper bound, since
|
|
/// only 'static is known to outlive disjoint universal regions.
|
|
/// Therefore, this method should only be used in diagnostic code,
|
|
/// where displaying *some* named universal region is better than
|
|
/// falling back to 'static.
|
|
#[instrument(level = "debug", skip(self))]
|
|
pub(crate) fn approx_universal_upper_bound(&self, r: RegionVid) -> RegionVid {
|
|
debug!("{}", self.region_value_str(r));
|
|
|
|
// Find the smallest universal region that contains all other
|
|
// universal regions within `region`.
|
|
let mut lub = self.universal_regions.fr_fn_body;
|
|
let r_scc = self.constraint_sccs.scc(r);
|
|
let static_r = self.universal_regions.fr_static;
|
|
for ur in self.scc_values.universal_regions_outlived_by(r_scc) {
|
|
let new_lub = self.universal_region_relations.postdom_upper_bound(lub, ur);
|
|
debug!(?ur, ?lub, ?new_lub);
|
|
// The upper bound of two non-static regions is static: this
|
|
// means we know nothing about the relationship between these
|
|
// two regions. Pick a 'better' one to use when constructing
|
|
// a diagnostic
|
|
if ur != static_r && lub != static_r && new_lub == static_r {
|
|
// Prefer the region with an `external_name` - this
|
|
// indicates that the region is early-bound, so working with
|
|
// it can produce a nicer error.
|
|
if self.region_definition(ur).external_name.is_some() {
|
|
lub = ur;
|
|
} else if self.region_definition(lub).external_name.is_some() {
|
|
// Leave lub unchanged
|
|
} else {
|
|
// If we get here, we don't have any reason to prefer
|
|
// one region over the other. Just pick the
|
|
// one with the lower index for now.
|
|
lub = std::cmp::min(ur, lub);
|
|
}
|
|
} else {
|
|
lub = new_lub;
|
|
}
|
|
}
|
|
|
|
debug!(?r, ?lub);
|
|
|
|
lub
|
|
}
|
|
|
|
/// Tests if `test` is true when applied to `lower_bound` at
|
|
/// `point`.
|
|
fn eval_verify_bound(
|
|
&self,
|
|
infcx: &InferCtxt<'tcx>,
|
|
generic_ty: Ty<'tcx>,
|
|
lower_bound: RegionVid,
|
|
verify_bound: &VerifyBound<'tcx>,
|
|
) -> bool {
|
|
debug!("eval_verify_bound(lower_bound={:?}, verify_bound={:?})", lower_bound, verify_bound);
|
|
|
|
match verify_bound {
|
|
VerifyBound::IfEq(verify_if_eq_b) => {
|
|
self.eval_if_eq(infcx, generic_ty, lower_bound, *verify_if_eq_b)
|
|
}
|
|
|
|
VerifyBound::IsEmpty => {
|
|
let lower_bound_scc = self.constraint_sccs.scc(lower_bound);
|
|
self.scc_values.elements_contained_in(lower_bound_scc).next().is_none()
|
|
}
|
|
|
|
VerifyBound::OutlivedBy(r) => {
|
|
let r_vid = self.to_region_vid(*r);
|
|
self.eval_outlives(r_vid, lower_bound)
|
|
}
|
|
|
|
VerifyBound::AnyBound(verify_bounds) => verify_bounds.iter().any(|verify_bound| {
|
|
self.eval_verify_bound(infcx, generic_ty, lower_bound, verify_bound)
|
|
}),
|
|
|
|
VerifyBound::AllBounds(verify_bounds) => verify_bounds.iter().all(|verify_bound| {
|
|
self.eval_verify_bound(infcx, generic_ty, lower_bound, verify_bound)
|
|
}),
|
|
}
|
|
}
|
|
|
|
fn eval_if_eq(
|
|
&self,
|
|
infcx: &InferCtxt<'tcx>,
|
|
generic_ty: Ty<'tcx>,
|
|
lower_bound: RegionVid,
|
|
verify_if_eq_b: ty::Binder<'tcx, VerifyIfEq<'tcx>>,
|
|
) -> bool {
|
|
let generic_ty = self.normalize_to_scc_representatives(infcx.tcx, generic_ty);
|
|
let verify_if_eq_b = self.normalize_to_scc_representatives(infcx.tcx, verify_if_eq_b);
|
|
match test_type_match::extract_verify_if_eq(infcx.tcx, &verify_if_eq_b, generic_ty) {
|
|
Some(r) => {
|
|
let r_vid = self.to_region_vid(r);
|
|
self.eval_outlives(r_vid, lower_bound)
|
|
}
|
|
None => false,
|
|
}
|
|
}
|
|
|
|
/// This is a conservative normalization procedure. It takes every
|
|
/// free region in `value` and replaces it with the
|
|
/// "representative" of its SCC (see `scc_representatives` field).
|
|
/// We are guaranteed that if two values normalize to the same
|
|
/// thing, then they are equal; this is a conservative check in
|
|
/// that they could still be equal even if they normalize to
|
|
/// different results. (For example, there might be two regions
|
|
/// with the same value that are not in the same SCC).
|
|
///
|
|
/// N.B., this is not an ideal approach and I would like to revisit
|
|
/// it. However, it works pretty well in practice. In particular,
|
|
/// this is needed to deal with projection outlives bounds like
|
|
///
|
|
/// ```text
|
|
/// <T as Foo<'0>>::Item: '1
|
|
/// ```
|
|
///
|
|
/// In particular, this routine winds up being important when
|
|
/// there are bounds like `where <T as Foo<'a>>::Item: 'b` in the
|
|
/// environment. In this case, if we can show that `'0 == 'a`,
|
|
/// and that `'b: '1`, then we know that the clause is
|
|
/// satisfied. In such cases, particularly due to limitations of
|
|
/// the trait solver =), we usually wind up with a where-clause like
|
|
/// `T: Foo<'a>` in scope, which thus forces `'0 == 'a` to be added as
|
|
/// a constraint, and thus ensures that they are in the same SCC.
|
|
///
|
|
/// So why can't we do a more correct routine? Well, we could
|
|
/// *almost* use the `relate_tys` code, but the way it is
|
|
/// currently setup it creates inference variables to deal with
|
|
/// higher-ranked things and so forth, and right now the inference
|
|
/// context is not permitted to make more inference variables. So
|
|
/// we use this kind of hacky solution.
|
|
fn normalize_to_scc_representatives<T>(&self, tcx: TyCtxt<'tcx>, value: T) -> T
|
|
where
|
|
T: TypeFoldable<TyCtxt<'tcx>>,
|
|
{
|
|
tcx.fold_regions(value, |r, _db| {
|
|
let vid = self.to_region_vid(r);
|
|
let scc = self.constraint_sccs.scc(vid);
|
|
let repr = self.scc_representatives[scc];
|
|
ty::Region::new_var(tcx, repr)
|
|
})
|
|
}
|
|
|
|
// Evaluate whether `sup_region == sub_region`.
|
|
fn eval_equal(&self, r1: RegionVid, r2: RegionVid) -> bool {
|
|
self.eval_outlives(r1, r2) && self.eval_outlives(r2, r1)
|
|
}
|
|
|
|
// Evaluate whether `sup_region: sub_region`.
|
|
#[instrument(skip(self), level = "debug", ret)]
|
|
fn eval_outlives(&self, sup_region: RegionVid, sub_region: RegionVid) -> bool {
|
|
debug!(
|
|
"sup_region's value = {:?} universal={:?}",
|
|
self.region_value_str(sup_region),
|
|
self.universal_regions.is_universal_region(sup_region),
|
|
);
|
|
debug!(
|
|
"sub_region's value = {:?} universal={:?}",
|
|
self.region_value_str(sub_region),
|
|
self.universal_regions.is_universal_region(sub_region),
|
|
);
|
|
|
|
let sub_region_scc = self.constraint_sccs.scc(sub_region);
|
|
let sup_region_scc = self.constraint_sccs.scc(sup_region);
|
|
|
|
// If we are checking that `'sup: 'sub`, and `'sub` contains
|
|
// some placeholder that `'sup` cannot name, then this is only
|
|
// true if `'sup` outlives static.
|
|
if !self.universe_compatible(sub_region_scc, sup_region_scc) {
|
|
debug!(
|
|
"sub universe `{sub_region_scc:?}` is not nameable \
|
|
by super `{sup_region_scc:?}`, promoting to static",
|
|
);
|
|
|
|
return self.eval_outlives(sup_region, self.universal_regions.fr_static);
|
|
}
|
|
|
|
// Both the `sub_region` and `sup_region` consist of the union
|
|
// of some number of universal regions (along with the union
|
|
// of various points in the CFG; ignore those points for
|
|
// now). Therefore, the sup-region outlives the sub-region if,
|
|
// for each universal region R1 in the sub-region, there
|
|
// exists some region R2 in the sup-region that outlives R1.
|
|
let universal_outlives =
|
|
self.scc_values.universal_regions_outlived_by(sub_region_scc).all(|r1| {
|
|
self.scc_values
|
|
.universal_regions_outlived_by(sup_region_scc)
|
|
.any(|r2| self.universal_region_relations.outlives(r2, r1))
|
|
});
|
|
|
|
if !universal_outlives {
|
|
debug!("sub region contains a universal region not present in super");
|
|
return false;
|
|
}
|
|
|
|
// Now we have to compare all the points in the sub region and make
|
|
// sure they exist in the sup region.
|
|
|
|
if self.universal_regions.is_universal_region(sup_region) {
|
|
// Micro-opt: universal regions contain all points.
|
|
debug!("super is universal and hence contains all points");
|
|
return true;
|
|
}
|
|
|
|
debug!("comparison between points in sup/sub");
|
|
|
|
self.scc_values.contains_points(sup_region_scc, sub_region_scc)
|
|
}
|
|
|
|
/// Once regions have been propagated, this method is used to see
|
|
/// whether any of the constraints were too strong. In particular,
|
|
/// we want to check for a case where a universally quantified
|
|
/// region exceeded its bounds. Consider:
|
|
/// ```compile_fail
|
|
/// fn foo<'a, 'b>(x: &'a u32) -> &'b u32 { x }
|
|
/// ```
|
|
/// In this case, returning `x` requires `&'a u32 <: &'b u32`
|
|
/// and hence we establish (transitively) a constraint that
|
|
/// `'a: 'b`. The `propagate_constraints` code above will
|
|
/// therefore add `end('a)` into the region for `'b` -- but we
|
|
/// have no evidence that `'b` outlives `'a`, so we want to report
|
|
/// an error.
|
|
///
|
|
/// If `propagated_outlives_requirements` is `Some`, then we will
|
|
/// push unsatisfied obligations into there. Otherwise, we'll
|
|
/// report them as errors.
|
|
fn check_universal_regions(
|
|
&self,
|
|
mut propagated_outlives_requirements: Option<&mut Vec<ClosureOutlivesRequirement<'tcx>>>,
|
|
errors_buffer: &mut RegionErrors<'tcx>,
|
|
) {
|
|
for (fr, fr_definition) in self.definitions.iter_enumerated() {
|
|
debug!(?fr, ?fr_definition);
|
|
match fr_definition.origin {
|
|
NllRegionVariableOrigin::FreeRegion => {
|
|
// Go through each of the universal regions `fr` and check that
|
|
// they did not grow too large, accumulating any requirements
|
|
// for our caller into the `outlives_requirements` vector.
|
|
self.check_universal_region(
|
|
fr,
|
|
&mut propagated_outlives_requirements,
|
|
errors_buffer,
|
|
);
|
|
}
|
|
|
|
NllRegionVariableOrigin::Placeholder(placeholder) => {
|
|
self.check_bound_universal_region(fr, placeholder, errors_buffer);
|
|
}
|
|
|
|
NllRegionVariableOrigin::Existential { .. } => {
|
|
// nothing to check here
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
/// Checks if Polonius has found any unexpected free region relations.
|
|
///
|
|
/// In Polonius terms, a "subset error" (or "illegal subset relation error") is the equivalent
|
|
/// of NLL's "checking if any region constraints were too strong": a placeholder origin `'a`
|
|
/// was unexpectedly found to be a subset of another placeholder origin `'b`, and means in NLL
|
|
/// terms that the "longer free region" `'a` outlived the "shorter free region" `'b`.
|
|
///
|
|
/// More details can be found in this blog post by Niko:
|
|
/// <https://smallcultfollowing.com/babysteps/blog/2019/01/17/polonius-and-region-errors/>
|
|
///
|
|
/// In the canonical example
|
|
/// ```compile_fail
|
|
/// fn foo<'a, 'b>(x: &'a u32) -> &'b u32 { x }
|
|
/// ```
|
|
/// returning `x` requires `&'a u32 <: &'b u32` and hence we establish (transitively) a
|
|
/// constraint that `'a: 'b`. It is an error that we have no evidence that this
|
|
/// constraint holds.
|
|
///
|
|
/// If `propagated_outlives_requirements` is `Some`, then we will
|
|
/// push unsatisfied obligations into there. Otherwise, we'll
|
|
/// report them as errors.
|
|
fn check_polonius_subset_errors(
|
|
&self,
|
|
mut propagated_outlives_requirements: Option<&mut Vec<ClosureOutlivesRequirement<'tcx>>>,
|
|
errors_buffer: &mut RegionErrors<'tcx>,
|
|
polonius_output: Rc<PoloniusOutput>,
|
|
) {
|
|
debug!(
|
|
"check_polonius_subset_errors: {} subset_errors",
|
|
polonius_output.subset_errors.len()
|
|
);
|
|
|
|
// Similarly to `check_universal_regions`: a free region relation, which was not explicitly
|
|
// declared ("known") was found by Polonius, so emit an error, or propagate the
|
|
// requirements for our caller into the `propagated_outlives_requirements` vector.
|
|
//
|
|
// Polonius doesn't model regions ("origins") as CFG-subsets or durations, but the
|
|
// `longer_fr` and `shorter_fr` terminology will still be used here, for consistency with
|
|
// the rest of the NLL infrastructure. The "subset origin" is the "longer free region",
|
|
// and the "superset origin" is the outlived "shorter free region".
|
|
//
|
|
// Note: Polonius will produce a subset error at every point where the unexpected
|
|
// `longer_fr`'s "placeholder loan" is contained in the `shorter_fr`. This can be helpful
|
|
// for diagnostics in the future, e.g. to point more precisely at the key locations
|
|
// requiring this constraint to hold. However, the error and diagnostics code downstream
|
|
// expects that these errors are not duplicated (and that they are in a certain order).
|
|
// Otherwise, diagnostics messages such as the ones giving names like `'1` to elided or
|
|
// anonymous lifetimes for example, could give these names differently, while others like
|
|
// the outlives suggestions or the debug output from `#[rustc_regions]` would be
|
|
// duplicated. The polonius subset errors are deduplicated here, while keeping the
|
|
// CFG-location ordering.
|
|
// We can iterate the HashMap here because the result is sorted afterwards.
|
|
#[allow(rustc::potential_query_instability)]
|
|
let mut subset_errors: Vec<_> = polonius_output
|
|
.subset_errors
|
|
.iter()
|
|
.flat_map(|(_location, subset_errors)| subset_errors.iter())
|
|
.collect();
|
|
subset_errors.sort();
|
|
subset_errors.dedup();
|
|
|
|
for (longer_fr, shorter_fr) in subset_errors.into_iter() {
|
|
debug!(
|
|
"check_polonius_subset_errors: subset_error longer_fr={:?},\
|
|
shorter_fr={:?}",
|
|
longer_fr, shorter_fr
|
|
);
|
|
|
|
let propagated = self.try_propagate_universal_region_error(
|
|
*longer_fr,
|
|
*shorter_fr,
|
|
&mut propagated_outlives_requirements,
|
|
);
|
|
if propagated == RegionRelationCheckResult::Error {
|
|
errors_buffer.push(RegionErrorKind::RegionError {
|
|
longer_fr: *longer_fr,
|
|
shorter_fr: *shorter_fr,
|
|
fr_origin: NllRegionVariableOrigin::FreeRegion,
|
|
is_reported: true,
|
|
});
|
|
}
|
|
}
|
|
|
|
// Handle the placeholder errors as usual, until the chalk-rustc-polonius triumvirate has
|
|
// a more complete picture on how to separate this responsibility.
|
|
for (fr, fr_definition) in self.definitions.iter_enumerated() {
|
|
match fr_definition.origin {
|
|
NllRegionVariableOrigin::FreeRegion => {
|
|
// handled by polonius above
|
|
}
|
|
|
|
NllRegionVariableOrigin::Placeholder(placeholder) => {
|
|
self.check_bound_universal_region(fr, placeholder, errors_buffer);
|
|
}
|
|
|
|
NllRegionVariableOrigin::Existential { .. } => {
|
|
// nothing to check here
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
/// Checks the final value for the free region `fr` to see if it
|
|
/// grew too large. In particular, examine what `end(X)` points
|
|
/// wound up in `fr`'s final value; for each `end(X)` where `X !=
|
|
/// fr`, we want to check that `fr: X`. If not, that's either an
|
|
/// error, or something we have to propagate to our creator.
|
|
///
|
|
/// Things that are to be propagated are accumulated into the
|
|
/// `outlives_requirements` vector.
|
|
#[instrument(skip(self, propagated_outlives_requirements, errors_buffer), level = "debug")]
|
|
fn check_universal_region(
|
|
&self,
|
|
longer_fr: RegionVid,
|
|
propagated_outlives_requirements: &mut Option<&mut Vec<ClosureOutlivesRequirement<'tcx>>>,
|
|
errors_buffer: &mut RegionErrors<'tcx>,
|
|
) {
|
|
let longer_fr_scc = self.constraint_sccs.scc(longer_fr);
|
|
|
|
// Because this free region must be in the ROOT universe, we
|
|
// know it cannot contain any bound universes.
|
|
assert!(self.scc_universes[longer_fr_scc] == ty::UniverseIndex::ROOT);
|
|
debug_assert!(self.scc_values.placeholders_contained_in(longer_fr_scc).next().is_none());
|
|
|
|
// Only check all of the relations for the main representative of each
|
|
// SCC, otherwise just check that we outlive said representative. This
|
|
// reduces the number of redundant relations propagated out of
|
|
// closures.
|
|
// Note that the representative will be a universal region if there is
|
|
// one in this SCC, so we will always check the representative here.
|
|
let representative = self.scc_representatives[longer_fr_scc];
|
|
if representative != longer_fr {
|
|
if let RegionRelationCheckResult::Error = self.check_universal_region_relation(
|
|
longer_fr,
|
|
representative,
|
|
propagated_outlives_requirements,
|
|
) {
|
|
errors_buffer.push(RegionErrorKind::RegionError {
|
|
longer_fr,
|
|
shorter_fr: representative,
|
|
fr_origin: NllRegionVariableOrigin::FreeRegion,
|
|
is_reported: true,
|
|
});
|
|
}
|
|
return;
|
|
}
|
|
|
|
// Find every region `o` such that `fr: o`
|
|
// (because `fr` includes `end(o)`).
|
|
let mut error_reported = false;
|
|
for shorter_fr in self.scc_values.universal_regions_outlived_by(longer_fr_scc) {
|
|
if let RegionRelationCheckResult::Error = self.check_universal_region_relation(
|
|
longer_fr,
|
|
shorter_fr,
|
|
propagated_outlives_requirements,
|
|
) {
|
|
// We only report the first region error. Subsequent errors are hidden so as
|
|
// not to overwhelm the user, but we do record them so as to potentially print
|
|
// better diagnostics elsewhere...
|
|
errors_buffer.push(RegionErrorKind::RegionError {
|
|
longer_fr,
|
|
shorter_fr,
|
|
fr_origin: NllRegionVariableOrigin::FreeRegion,
|
|
is_reported: !error_reported,
|
|
});
|
|
|
|
error_reported = true;
|
|
}
|
|
}
|
|
}
|
|
|
|
/// Checks that we can prove that `longer_fr: shorter_fr`. If we can't we attempt to propagate
|
|
/// the constraint outward (e.g. to a closure environment), but if that fails, there is an
|
|
/// error.
|
|
fn check_universal_region_relation(
|
|
&self,
|
|
longer_fr: RegionVid,
|
|
shorter_fr: RegionVid,
|
|
propagated_outlives_requirements: &mut Option<&mut Vec<ClosureOutlivesRequirement<'tcx>>>,
|
|
) -> RegionRelationCheckResult {
|
|
// If it is known that `fr: o`, carry on.
|
|
if self.universal_region_relations.outlives(longer_fr, shorter_fr) {
|
|
RegionRelationCheckResult::Ok
|
|
} else {
|
|
// If we are not in a context where we can't propagate errors, or we
|
|
// could not shrink `fr` to something smaller, then just report an
|
|
// error.
|
|
//
|
|
// Note: in this case, we use the unapproximated regions to report the
|
|
// error. This gives better error messages in some cases.
|
|
self.try_propagate_universal_region_error(
|
|
longer_fr,
|
|
shorter_fr,
|
|
propagated_outlives_requirements,
|
|
)
|
|
}
|
|
}
|
|
|
|
/// Attempt to propagate a region error (e.g. `'a: 'b`) that is not met to a closure's
|
|
/// creator. If we cannot, then the caller should report an error to the user.
|
|
fn try_propagate_universal_region_error(
|
|
&self,
|
|
longer_fr: RegionVid,
|
|
shorter_fr: RegionVid,
|
|
propagated_outlives_requirements: &mut Option<&mut Vec<ClosureOutlivesRequirement<'tcx>>>,
|
|
) -> RegionRelationCheckResult {
|
|
if let Some(propagated_outlives_requirements) = propagated_outlives_requirements {
|
|
// Shrink `longer_fr` until we find a non-local region (if we do).
|
|
// We'll call it `fr-` -- it's ever so slightly smaller than
|
|
// `longer_fr`.
|
|
if let Some(fr_minus) = self.universal_region_relations.non_local_lower_bound(longer_fr)
|
|
{
|
|
debug!("try_propagate_universal_region_error: fr_minus={:?}", fr_minus);
|
|
|
|
let blame_span_category = self.find_outlives_blame_span(
|
|
longer_fr,
|
|
NllRegionVariableOrigin::FreeRegion,
|
|
shorter_fr,
|
|
);
|
|
|
|
// Grow `shorter_fr` until we find some non-local regions. (We
|
|
// always will.) We'll call them `shorter_fr+` -- they're ever
|
|
// so slightly larger than `shorter_fr`.
|
|
let shorter_fr_plus =
|
|
self.universal_region_relations.non_local_upper_bounds(shorter_fr);
|
|
debug!(
|
|
"try_propagate_universal_region_error: shorter_fr_plus={:?}",
|
|
shorter_fr_plus
|
|
);
|
|
for fr in shorter_fr_plus {
|
|
// Push the constraint `fr-: shorter_fr+`
|
|
propagated_outlives_requirements.push(ClosureOutlivesRequirement {
|
|
subject: ClosureOutlivesSubject::Region(fr_minus),
|
|
outlived_free_region: fr,
|
|
blame_span: blame_span_category.1.span,
|
|
category: blame_span_category.0,
|
|
});
|
|
}
|
|
return RegionRelationCheckResult::Propagated;
|
|
}
|
|
}
|
|
|
|
RegionRelationCheckResult::Error
|
|
}
|
|
|
|
fn check_bound_universal_region(
|
|
&self,
|
|
longer_fr: RegionVid,
|
|
placeholder: ty::PlaceholderRegion,
|
|
errors_buffer: &mut RegionErrors<'tcx>,
|
|
) {
|
|
debug!("check_bound_universal_region(fr={:?}, placeholder={:?})", longer_fr, placeholder,);
|
|
|
|
let longer_fr_scc = self.constraint_sccs.scc(longer_fr);
|
|
debug!("check_bound_universal_region: longer_fr_scc={:?}", longer_fr_scc,);
|
|
|
|
for error_element in self.scc_values.elements_contained_in(longer_fr_scc) {
|
|
match error_element {
|
|
RegionElement::Location(_) | RegionElement::RootUniversalRegion(_) => {}
|
|
// If we have some bound universal region `'a`, then the only
|
|
// elements it can contain is itself -- we don't know anything
|
|
// else about it!
|
|
RegionElement::PlaceholderRegion(placeholder1) => {
|
|
if placeholder == placeholder1 {
|
|
continue;
|
|
}
|
|
}
|
|
}
|
|
|
|
errors_buffer.push(RegionErrorKind::BoundUniversalRegionError {
|
|
longer_fr,
|
|
error_element,
|
|
placeholder,
|
|
});
|
|
|
|
// Stop after the first error, it gets too noisy otherwise, and does not provide more information.
|
|
break;
|
|
}
|
|
debug!("check_bound_universal_region: all bounds satisfied");
|
|
}
|
|
|
|
#[instrument(level = "debug", skip(self, infcx, errors_buffer))]
|
|
fn check_member_constraints(
|
|
&self,
|
|
infcx: &InferCtxt<'tcx>,
|
|
errors_buffer: &mut RegionErrors<'tcx>,
|
|
) {
|
|
let member_constraints = self.member_constraints.clone();
|
|
for m_c_i in member_constraints.all_indices() {
|
|
debug!(?m_c_i);
|
|
let m_c = &member_constraints[m_c_i];
|
|
let member_region_vid = m_c.member_region_vid;
|
|
debug!(
|
|
?member_region_vid,
|
|
value = ?self.region_value_str(member_region_vid),
|
|
);
|
|
let choice_regions = member_constraints.choice_regions(m_c_i);
|
|
debug!(?choice_regions);
|
|
|
|
// Did the member region wind up equal to any of the option regions?
|
|
if let Some(o) =
|
|
choice_regions.iter().find(|&&o_r| self.eval_equal(o_r, m_c.member_region_vid))
|
|
{
|
|
debug!("evaluated as equal to {:?}", o);
|
|
continue;
|
|
}
|
|
|
|
// If not, report an error.
|
|
let member_region = ty::Region::new_var(infcx.tcx, member_region_vid);
|
|
errors_buffer.push(RegionErrorKind::UnexpectedHiddenRegion {
|
|
span: m_c.definition_span,
|
|
hidden_ty: m_c.hidden_ty,
|
|
key: m_c.key,
|
|
member_region,
|
|
});
|
|
}
|
|
}
|
|
|
|
/// We have a constraint `fr1: fr2` that is not satisfied, where
|
|
/// `fr2` represents some universal region. Here, `r` is some
|
|
/// region where we know that `fr1: r` and this function has the
|
|
/// job of determining whether `r` is "to blame" for the fact that
|
|
/// `fr1: fr2` is required.
|
|
///
|
|
/// This is true under two conditions:
|
|
///
|
|
/// - `r == fr2`
|
|
/// - `fr2` is `'static` and `r` is some placeholder in a universe
|
|
/// that cannot be named by `fr1`; in that case, we will require
|
|
/// that `fr1: 'static` because it is the only way to `fr1: r` to
|
|
/// be satisfied. (See `add_incompatible_universe`.)
|
|
pub(crate) fn provides_universal_region(
|
|
&self,
|
|
r: RegionVid,
|
|
fr1: RegionVid,
|
|
fr2: RegionVid,
|
|
) -> bool {
|
|
debug!("provides_universal_region(r={:?}, fr1={:?}, fr2={:?})", r, fr1, fr2);
|
|
let result = {
|
|
r == fr2 || {
|
|
fr2 == self.universal_regions.fr_static && self.cannot_name_placeholder(fr1, r)
|
|
}
|
|
};
|
|
debug!("provides_universal_region: result = {:?}", result);
|
|
result
|
|
}
|
|
|
|
/// If `r2` represents a placeholder region, then this returns
|
|
/// `true` if `r1` cannot name that placeholder in its
|
|
/// value; otherwise, returns `false`.
|
|
pub(crate) fn cannot_name_placeholder(&self, r1: RegionVid, r2: RegionVid) -> bool {
|
|
debug!("cannot_name_value_of(r1={:?}, r2={:?})", r1, r2);
|
|
|
|
match self.definitions[r2].origin {
|
|
NllRegionVariableOrigin::Placeholder(placeholder) => {
|
|
let universe1 = self.definitions[r1].universe;
|
|
debug!(
|
|
"cannot_name_value_of: universe1={:?} placeholder={:?}",
|
|
universe1, placeholder
|
|
);
|
|
universe1.cannot_name(placeholder.universe)
|
|
}
|
|
|
|
NllRegionVariableOrigin::FreeRegion | NllRegionVariableOrigin::Existential { .. } => {
|
|
false
|
|
}
|
|
}
|
|
}
|
|
|
|
/// Finds a good `ObligationCause` to blame for the fact that `fr1` outlives `fr2`.
|
|
pub(crate) fn find_outlives_blame_span(
|
|
&self,
|
|
fr1: RegionVid,
|
|
fr1_origin: NllRegionVariableOrigin,
|
|
fr2: RegionVid,
|
|
) -> (ConstraintCategory<'tcx>, ObligationCause<'tcx>) {
|
|
let BlameConstraint { category, cause, .. } = self
|
|
.best_blame_constraint(fr1, fr1_origin, |r| self.provides_universal_region(r, fr1, fr2))
|
|
.0;
|
|
(category, cause)
|
|
}
|
|
|
|
/// Walks the graph of constraints (where `'a: 'b` is considered
|
|
/// an edge `'a -> 'b`) to find all paths from `from_region` to
|
|
/// `to_region`. The paths are accumulated into the vector
|
|
/// `results`. The paths are stored as a series of
|
|
/// `ConstraintIndex` values -- in other words, a list of *edges*.
|
|
///
|
|
/// Returns: a series of constraints as well as the region `R`
|
|
/// that passed the target test.
|
|
pub(crate) fn find_constraint_paths_between_regions(
|
|
&self,
|
|
from_region: RegionVid,
|
|
target_test: impl Fn(RegionVid) -> bool,
|
|
) -> Option<(Vec<OutlivesConstraint<'tcx>>, RegionVid)> {
|
|
let mut context = IndexVec::from_elem(Trace::NotVisited, &self.definitions);
|
|
context[from_region] = Trace::StartRegion;
|
|
|
|
// Use a deque so that we do a breadth-first search. We will
|
|
// stop at the first match, which ought to be the shortest
|
|
// path (fewest constraints).
|
|
let mut deque = VecDeque::new();
|
|
deque.push_back(from_region);
|
|
|
|
while let Some(r) = deque.pop_front() {
|
|
debug!(
|
|
"find_constraint_paths_between_regions: from_region={:?} r={:?} value={}",
|
|
from_region,
|
|
r,
|
|
self.region_value_str(r),
|
|
);
|
|
|
|
// Check if we reached the region we were looking for. If so,
|
|
// we can reconstruct the path that led to it and return it.
|
|
if target_test(r) {
|
|
let mut result = vec![];
|
|
let mut p = r;
|
|
loop {
|
|
match context[p].clone() {
|
|
Trace::NotVisited => {
|
|
bug!("found unvisited region {:?} on path to {:?}", p, r)
|
|
}
|
|
|
|
Trace::FromOutlivesConstraint(c) => {
|
|
p = c.sup;
|
|
result.push(c);
|
|
}
|
|
|
|
Trace::StartRegion => {
|
|
result.reverse();
|
|
return Some((result, r));
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
// Otherwise, walk over the outgoing constraints and
|
|
// enqueue any regions we find, keeping track of how we
|
|
// reached them.
|
|
|
|
// A constraint like `'r: 'x` can come from our constraint
|
|
// graph.
|
|
let fr_static = self.universal_regions.fr_static;
|
|
let outgoing_edges_from_graph =
|
|
self.constraint_graph.outgoing_edges(r, &self.constraints, fr_static);
|
|
|
|
// Always inline this closure because it can be hot.
|
|
let mut handle_constraint = #[inline(always)]
|
|
|constraint: OutlivesConstraint<'tcx>| {
|
|
debug_assert_eq!(constraint.sup, r);
|
|
let sub_region = constraint.sub;
|
|
if let Trace::NotVisited = context[sub_region] {
|
|
context[sub_region] = Trace::FromOutlivesConstraint(constraint);
|
|
deque.push_back(sub_region);
|
|
}
|
|
};
|
|
|
|
// This loop can be hot.
|
|
for constraint in outgoing_edges_from_graph {
|
|
handle_constraint(constraint);
|
|
}
|
|
|
|
// Member constraints can also give rise to `'r: 'x` edges that
|
|
// were not part of the graph initially, so watch out for those.
|
|
// (But they are extremely rare; this loop is very cold.)
|
|
for constraint in self.applied_member_constraints(self.constraint_sccs.scc(r)) {
|
|
let p_c = &self.member_constraints[constraint.member_constraint_index];
|
|
let constraint = OutlivesConstraint {
|
|
sup: r,
|
|
sub: constraint.min_choice,
|
|
locations: Locations::All(p_c.definition_span),
|
|
span: p_c.definition_span,
|
|
category: ConstraintCategory::OpaqueType,
|
|
variance_info: ty::VarianceDiagInfo::default(),
|
|
from_closure: false,
|
|
};
|
|
handle_constraint(constraint);
|
|
}
|
|
}
|
|
|
|
None
|
|
}
|
|
|
|
/// Finds some region R such that `fr1: R` and `R` is live at `location`.
|
|
#[instrument(skip(self), level = "trace", ret)]
|
|
pub(crate) fn find_sub_region_live_at(&self, fr1: RegionVid, location: Location) -> RegionVid {
|
|
trace!(scc = ?self.constraint_sccs.scc(fr1));
|
|
trace!(universe = ?self.scc_universes[self.constraint_sccs.scc(fr1)]);
|
|
self.find_constraint_paths_between_regions(fr1, |r| {
|
|
// First look for some `r` such that `fr1: r` and `r` is live at `location`
|
|
trace!(?r, liveness_constraints=?self.liveness_constraints.pretty_print_live_points(r));
|
|
self.liveness_constraints.is_live_at(r, location)
|
|
})
|
|
.or_else(|| {
|
|
// If we fail to find that, we may find some `r` such that
|
|
// `fr1: r` and `r` is a placeholder from some universe
|
|
// `fr1` cannot name. This would force `fr1` to be
|
|
// `'static`.
|
|
self.find_constraint_paths_between_regions(fr1, |r| {
|
|
self.cannot_name_placeholder(fr1, r)
|
|
})
|
|
})
|
|
.or_else(|| {
|
|
// If we fail to find THAT, it may be that `fr1` is a
|
|
// placeholder that cannot "fit" into its SCC. In that
|
|
// case, there should be some `r` where `fr1: r` and `fr1` is a
|
|
// placeholder that `r` cannot name. We can blame that
|
|
// edge.
|
|
//
|
|
// Remember that if `R1: R2`, then the universe of R1
|
|
// must be able to name the universe of R2, because R2 will
|
|
// be at least `'empty(Universe(R2))`, and `R1` must be at
|
|
// larger than that.
|
|
self.find_constraint_paths_between_regions(fr1, |r| {
|
|
self.cannot_name_placeholder(r, fr1)
|
|
})
|
|
})
|
|
.map(|(_path, r)| r)
|
|
.unwrap()
|
|
}
|
|
|
|
/// Get the region outlived by `longer_fr` and live at `element`.
|
|
pub(crate) fn region_from_element(
|
|
&self,
|
|
longer_fr: RegionVid,
|
|
element: &RegionElement,
|
|
) -> RegionVid {
|
|
match *element {
|
|
RegionElement::Location(l) => self.find_sub_region_live_at(longer_fr, l),
|
|
RegionElement::RootUniversalRegion(r) => r,
|
|
RegionElement::PlaceholderRegion(error_placeholder) => self
|
|
.definitions
|
|
.iter_enumerated()
|
|
.find_map(|(r, definition)| match definition.origin {
|
|
NllRegionVariableOrigin::Placeholder(p) if p == error_placeholder => Some(r),
|
|
_ => None,
|
|
})
|
|
.unwrap(),
|
|
}
|
|
}
|
|
|
|
/// Get the region definition of `r`.
|
|
pub(crate) fn region_definition(&self, r: RegionVid) -> &RegionDefinition<'tcx> {
|
|
&self.definitions[r]
|
|
}
|
|
|
|
/// Check if the SCC of `r` contains `upper`.
|
|
pub(crate) fn upper_bound_in_region_scc(&self, r: RegionVid, upper: RegionVid) -> bool {
|
|
let r_scc = self.constraint_sccs.scc(r);
|
|
self.scc_values.contains(r_scc, upper)
|
|
}
|
|
|
|
pub(crate) fn universal_regions(&self) -> &UniversalRegions<'tcx> {
|
|
self.universal_regions.as_ref()
|
|
}
|
|
|
|
/// Tries to find the best constraint to blame for the fact that
|
|
/// `R: from_region`, where `R` is some region that meets
|
|
/// `target_test`. This works by following the constraint graph,
|
|
/// creating a constraint path that forces `R` to outlive
|
|
/// `from_region`, and then finding the best choices within that
|
|
/// path to blame.
|
|
#[instrument(level = "debug", skip(self, target_test))]
|
|
pub(crate) fn best_blame_constraint(
|
|
&self,
|
|
from_region: RegionVid,
|
|
from_region_origin: NllRegionVariableOrigin,
|
|
target_test: impl Fn(RegionVid) -> bool,
|
|
) -> (BlameConstraint<'tcx>, Vec<ExtraConstraintInfo>) {
|
|
// Find all paths
|
|
let (path, target_region) =
|
|
self.find_constraint_paths_between_regions(from_region, target_test).unwrap();
|
|
debug!(
|
|
"path={:#?}",
|
|
path.iter()
|
|
.map(|c| format!(
|
|
"{:?} ({:?}: {:?})",
|
|
c,
|
|
self.constraint_sccs.scc(c.sup),
|
|
self.constraint_sccs.scc(c.sub),
|
|
))
|
|
.collect::<Vec<_>>()
|
|
);
|
|
|
|
let mut extra_info = vec![];
|
|
for constraint in path.iter() {
|
|
let outlived = constraint.sub;
|
|
let Some(origin) = self.var_infos.get(outlived) else {
|
|
continue;
|
|
};
|
|
let RegionVariableOrigin::Nll(NllRegionVariableOrigin::Placeholder(p)) = origin.origin
|
|
else {
|
|
continue;
|
|
};
|
|
debug!(?constraint, ?p);
|
|
let ConstraintCategory::Predicate(span) = constraint.category else {
|
|
continue;
|
|
};
|
|
extra_info.push(ExtraConstraintInfo::PlaceholderFromPredicate(span));
|
|
// We only want to point to one
|
|
break;
|
|
}
|
|
|
|
// We try to avoid reporting a `ConstraintCategory::Predicate` as our best constraint.
|
|
// Instead, we use it to produce an improved `ObligationCauseCode`.
|
|
// FIXME - determine what we should do if we encounter multiple `ConstraintCategory::Predicate`
|
|
// constraints. Currently, we just pick the first one.
|
|
let cause_code = path
|
|
.iter()
|
|
.find_map(|constraint| {
|
|
if let ConstraintCategory::Predicate(predicate_span) = constraint.category {
|
|
// We currently do not store the `DefId` in the `ConstraintCategory`
|
|
// for performances reasons. The error reporting code used by NLL only
|
|
// uses the span, so this doesn't cause any problems at the moment.
|
|
Some(ObligationCauseCode::BindingObligation(
|
|
CRATE_DEF_ID.to_def_id(),
|
|
predicate_span,
|
|
))
|
|
} else {
|
|
None
|
|
}
|
|
})
|
|
.unwrap_or_else(|| ObligationCauseCode::MiscObligation);
|
|
|
|
// Classify each of the constraints along the path.
|
|
let mut categorized_path: Vec<BlameConstraint<'tcx>> = path
|
|
.iter()
|
|
.map(|constraint| BlameConstraint {
|
|
category: constraint.category,
|
|
from_closure: constraint.from_closure,
|
|
cause: ObligationCause::new(constraint.span, CRATE_DEF_ID, cause_code.clone()),
|
|
variance_info: constraint.variance_info,
|
|
outlives_constraint: *constraint,
|
|
})
|
|
.collect();
|
|
debug!("categorized_path={:#?}", categorized_path);
|
|
|
|
// To find the best span to cite, we first try to look for the
|
|
// final constraint that is interesting and where the `sup` is
|
|
// not unified with the ultimate target region. The reason
|
|
// for this is that we have a chain of constraints that lead
|
|
// from the source to the target region, something like:
|
|
//
|
|
// '0: '1 ('0 is the source)
|
|
// '1: '2
|
|
// '2: '3
|
|
// '3: '4
|
|
// '4: '5
|
|
// '5: '6 ('6 is the target)
|
|
//
|
|
// Some of those regions are unified with `'6` (in the same
|
|
// SCC). We want to screen those out. After that point, the
|
|
// "closest" constraint we have to the end is going to be the
|
|
// most likely to be the point where the value escapes -- but
|
|
// we still want to screen for an "interesting" point to
|
|
// highlight (e.g., a call site or something).
|
|
let target_scc = self.constraint_sccs.scc(target_region);
|
|
let mut range = 0..path.len();
|
|
|
|
// As noted above, when reporting an error, there is typically a chain of constraints
|
|
// leading from some "source" region which must outlive some "target" region.
|
|
// In most cases, we prefer to "blame" the constraints closer to the target --
|
|
// but there is one exception. When constraints arise from higher-ranked subtyping,
|
|
// we generally prefer to blame the source value,
|
|
// as the "target" in this case tends to be some type annotation that the user gave.
|
|
// Therefore, if we find that the region origin is some instantiation
|
|
// of a higher-ranked region, we start our search from the "source" point
|
|
// rather than the "target", and we also tweak a few other things.
|
|
//
|
|
// An example might be this bit of Rust code:
|
|
//
|
|
// ```rust
|
|
// let x: fn(&'static ()) = |_| {};
|
|
// let y: for<'a> fn(&'a ()) = x;
|
|
// ```
|
|
//
|
|
// In MIR, this will be converted into a combination of assignments and type ascriptions.
|
|
// In particular, the 'static is imposed through a type ascription:
|
|
//
|
|
// ```rust
|
|
// x = ...;
|
|
// AscribeUserType(x, fn(&'static ())
|
|
// y = x;
|
|
// ```
|
|
//
|
|
// We wind up ultimately with constraints like
|
|
//
|
|
// ```rust
|
|
// !a: 'temp1 // from the `y = x` statement
|
|
// 'temp1: 'temp2
|
|
// 'temp2: 'static // from the AscribeUserType
|
|
// ```
|
|
//
|
|
// and here we prefer to blame the source (the y = x statement).
|
|
let blame_source = match from_region_origin {
|
|
NllRegionVariableOrigin::FreeRegion
|
|
| NllRegionVariableOrigin::Existential { from_forall: false } => true,
|
|
NllRegionVariableOrigin::Placeholder(_)
|
|
| NllRegionVariableOrigin::Existential { from_forall: true } => false,
|
|
};
|
|
|
|
let find_region = |i: &usize| {
|
|
let constraint = &path[*i];
|
|
|
|
let constraint_sup_scc = self.constraint_sccs.scc(constraint.sup);
|
|
|
|
if blame_source {
|
|
match categorized_path[*i].category {
|
|
ConstraintCategory::OpaqueType
|
|
| ConstraintCategory::Boring
|
|
| ConstraintCategory::BoringNoLocation
|
|
| ConstraintCategory::Internal
|
|
| ConstraintCategory::Predicate(_) => false,
|
|
ConstraintCategory::TypeAnnotation
|
|
| ConstraintCategory::Return(_)
|
|
| ConstraintCategory::Yield => true,
|
|
_ => constraint_sup_scc != target_scc,
|
|
}
|
|
} else {
|
|
!matches!(
|
|
categorized_path[*i].category,
|
|
ConstraintCategory::OpaqueType
|
|
| ConstraintCategory::Boring
|
|
| ConstraintCategory::BoringNoLocation
|
|
| ConstraintCategory::Internal
|
|
| ConstraintCategory::Predicate(_)
|
|
)
|
|
}
|
|
};
|
|
|
|
let best_choice =
|
|
if blame_source { range.rev().find(find_region) } else { range.find(find_region) };
|
|
|
|
debug!(?best_choice, ?blame_source, ?extra_info);
|
|
|
|
if let Some(i) = best_choice {
|
|
if let Some(next) = categorized_path.get(i + 1) {
|
|
if matches!(categorized_path[i].category, ConstraintCategory::Return(_))
|
|
&& next.category == ConstraintCategory::OpaqueType
|
|
{
|
|
// The return expression is being influenced by the return type being
|
|
// impl Trait, point at the return type and not the return expr.
|
|
return (next.clone(), extra_info);
|
|
}
|
|
}
|
|
|
|
if categorized_path[i].category == ConstraintCategory::Return(ReturnConstraint::Normal)
|
|
{
|
|
let field = categorized_path.iter().find_map(|p| {
|
|
if let ConstraintCategory::ClosureUpvar(f) = p.category {
|
|
Some(f)
|
|
} else {
|
|
None
|
|
}
|
|
});
|
|
|
|
if let Some(field) = field {
|
|
categorized_path[i].category =
|
|
ConstraintCategory::Return(ReturnConstraint::ClosureUpvar(field));
|
|
}
|
|
}
|
|
|
|
return (categorized_path[i].clone(), extra_info);
|
|
}
|
|
|
|
// If that search fails, that is.. unusual. Maybe everything
|
|
// is in the same SCC or something. In that case, find what
|
|
// appears to be the most interesting point to report to the
|
|
// user via an even more ad-hoc guess.
|
|
categorized_path.sort_by_key(|p| p.category);
|
|
debug!("sorted_path={:#?}", categorized_path);
|
|
|
|
(categorized_path.remove(0), extra_info)
|
|
}
|
|
|
|
pub(crate) fn universe_info(&self, universe: ty::UniverseIndex) -> UniverseInfo<'tcx> {
|
|
// Query canonicalization can create local superuniverses (for example in
|
|
// `InferCtx::query_response_instantiation_guess`), but they don't have an associated
|
|
// `UniverseInfo` explaining why they were created.
|
|
// This can cause ICEs if these causes are accessed in diagnostics, for example in issue
|
|
// #114907 where this happens via liveness and dropck outlives results.
|
|
// Therefore, we return a default value in case that happens, which should at worst emit a
|
|
// suboptimal error, instead of the ICE.
|
|
self.universe_causes.get(&universe).cloned().unwrap_or_else(|| UniverseInfo::other())
|
|
}
|
|
|
|
/// Tries to find the terminator of the loop in which the region 'r' resides.
|
|
/// Returns the location of the terminator if found.
|
|
pub(crate) fn find_loop_terminator_location(
|
|
&self,
|
|
r: RegionVid,
|
|
body: &Body<'_>,
|
|
) -> Option<Location> {
|
|
let scc = self.constraint_sccs.scc(r);
|
|
let locations = self.scc_values.locations_outlived_by(scc);
|
|
for location in locations {
|
|
let bb = &body[location.block];
|
|
if let Some(terminator) = &bb.terminator {
|
|
// terminator of a loop should be TerminatorKind::FalseUnwind
|
|
if let TerminatorKind::FalseUnwind { .. } = terminator.kind {
|
|
return Some(location);
|
|
}
|
|
}
|
|
}
|
|
None
|
|
}
|
|
|
|
/// Access to the SCC constraint graph.
|
|
pub(crate) fn constraint_sccs(&self) -> &Sccs<RegionVid, ConstraintSccIndex> {
|
|
self.constraint_sccs.as_ref()
|
|
}
|
|
|
|
/// Access to the region graph, built from the outlives constraints.
|
|
pub(crate) fn region_graph(&self) -> RegionGraph<'_, 'tcx, graph::Normal> {
|
|
self.constraint_graph.region_graph(&self.constraints, self.universal_regions.fr_static)
|
|
}
|
|
|
|
/// Returns whether the given region is considered live at all points: whether it is a
|
|
/// placeholder or a free region.
|
|
pub(crate) fn is_region_live_at_all_points(&self, region: RegionVid) -> bool {
|
|
// FIXME: there must be a cleaner way to find this information. At least, when
|
|
// higher-ranked subtyping is abstracted away from the borrowck main path, we'll only
|
|
// need to check whether this is a universal region.
|
|
let origin = self.region_definition(region).origin;
|
|
let live_at_all_points = matches!(
|
|
origin,
|
|
NllRegionVariableOrigin::Placeholder(_) | NllRegionVariableOrigin::FreeRegion
|
|
);
|
|
live_at_all_points
|
|
}
|
|
|
|
/// Returns whether the `loan_idx` is live at the given `location`: whether its issuing
|
|
/// region is contained within the type of a variable that is live at this point.
|
|
/// Note: for now, the sets of live loans is only available when using `-Zpolonius=next`.
|
|
pub(crate) fn is_loan_live_at(&self, loan_idx: BorrowIndex, location: Location) -> bool {
|
|
let point = self.liveness_constraints.point_from_location(location);
|
|
self.liveness_constraints.is_loan_live_at(loan_idx, point)
|
|
}
|
|
}
|
|
|
|
impl<'tcx> RegionDefinition<'tcx> {
|
|
fn new(universe: ty::UniverseIndex, rv_origin: RegionVariableOrigin) -> Self {
|
|
// Create a new region definition. Note that, for free
|
|
// regions, the `external_name` field gets updated later in
|
|
// `init_universal_regions`.
|
|
|
|
let origin = match rv_origin {
|
|
RegionVariableOrigin::Nll(origin) => origin,
|
|
_ => NllRegionVariableOrigin::Existential { from_forall: false },
|
|
};
|
|
|
|
Self { origin, universe, external_name: None }
|
|
}
|
|
}
|
|
|
|
#[derive(Clone, Debug)]
|
|
pub struct BlameConstraint<'tcx> {
|
|
pub category: ConstraintCategory<'tcx>,
|
|
pub from_closure: bool,
|
|
pub cause: ObligationCause<'tcx>,
|
|
pub variance_info: ty::VarianceDiagInfo<'tcx>,
|
|
pub outlives_constraint: OutlivesConstraint<'tcx>,
|
|
}
|