rustc/vendor/regex-automata/tests/hybrid/api.rs

use std::error::Error;

use regex_automata::{
    hybrid::{
        dfa::{self, DFA},
        regex::Regex,
        OverlappingState,
    },
    nfa::thompson,
    HalfMatch, MatchError, MatchKind, MultiMatch,
};

use crate::util::{BunkPrefilter, SubstringPrefilter};

// Tests that too many cache resets cause the lazy DFA to quit.
//
// We only test this on 64-bit because the test is gingerly crafted based on
// implementation details of cache sizes. It's not a great test because of
// that, but it does check some interesting properties around how positions are
// reported when a search "gives up."
#[test]
#[cfg(target_pointer_width = "64")]
fn too_many_cache_resets_cause_quit() -> Result<(), Box<dyn Error>> {
    // This is a carefully chosen regex. The idea is to pick one that requires
    // some decent number of states (hence the bounded repetition). But we
    // specifically choose to create a class with an ASCII letter and a
    // non-ASCII letter so that we can check that no new states are created
    // once the cache is full. Namely, if we fill up the cache on a haystack
    // of 'a's, then in order to match one 'β', a new state will need to be
    // created since a 'β' is encoded with multiple bytes. Since there's no
    // room for this state, the search should quit at the very first position.
    let pattern = r"[aβ]{100}";
    let dfa = DFA::builder()
        .configure(
            // Configure it so that we have the minimum cache capacity
            // possible. And that if any resets occur, the search quits.
            DFA::config()
                .skip_cache_capacity_check(true)
                .cache_capacity(0)
                .minimum_cache_clear_count(Some(0)),
        )
        .build(pattern)?;
    let mut cache = dfa.create_cache();

    let haystack = "a".repeat(101).into_bytes();
    let err = MatchError::GaveUp { offset: 25 };
    assert_eq!(dfa.find_earliest_fwd(&mut cache, &haystack), Err(err.clone()));
    assert_eq!(dfa.find_leftmost_fwd(&mut cache, &haystack), Err(err.clone()));
    assert_eq!(
        dfa.find_overlapping_fwd(
            &mut cache,
            &haystack,
            &mut OverlappingState::start()
        ),
        Err(err.clone())
    );

    let haystack = "β".repeat(101).into_bytes();
    let err = MatchError::GaveUp { offset: 0 };
    assert_eq!(dfa.find_earliest_fwd(&mut cache, &haystack), Err(err));
    // no need to test that other find routines quit, since we did that above

    // OK, if we reset the cache, then we should be able to create more states
    // and make more progress with searching for betas.
    cache.reset(&dfa);
    let err = MatchError::GaveUp { offset: 26 };
    assert_eq!(dfa.find_earliest_fwd(&mut cache, &haystack), Err(err));

    // ... switching back to ASCII still makes progress since it just needs to
    // set transitions on existing states!
    let haystack = "a".repeat(101).into_bytes();
    let err = MatchError::GaveUp { offset: 13 };
    assert_eq!(dfa.find_earliest_fwd(&mut cache, &haystack), Err(err));

    Ok(())
}

// Tests that quit bytes in the forward direction work correctly.
#[test]
fn quit_fwd() -> Result<(), Box<dyn Error>> {
    let dfa = DFA::builder()
        .configure(DFA::config().quit(b'x', true))
        .build("[[:word:]]+$")?;
    let mut cache = dfa.create_cache();

    assert_eq!(
        dfa.find_earliest_fwd(&mut cache, b"abcxyz"),
        Err(MatchError::Quit { byte: b'x', offset: 3 })
    );
    assert_eq!(
        dfa.find_leftmost_fwd(&mut cache, b"abcxyz"),
        Err(MatchError::Quit { byte: b'x', offset: 3 })
    );
    assert_eq!(
        dfa.find_overlapping_fwd(
            &mut cache,
            b"abcxyz",
            &mut OverlappingState::start()
        ),
        Err(MatchError::Quit { byte: b'x', offset: 3 })
    );

    Ok(())
}

// Tests that quit bytes in the reverse direction work correctly.
#[test]
fn quit_rev() -> Result<(), Box<dyn Error>> {
    let dfa = DFA::builder()
        .configure(DFA::config().quit(b'x', true))
        .thompson(thompson::Config::new().reverse(true))
        .build("^[[:word:]]+")?;
    let mut cache = dfa.create_cache();

    assert_eq!(
        dfa.find_earliest_rev(&mut cache, b"abcxyz"),
        Err(MatchError::Quit { byte: b'x', offset: 3 })
    );
    assert_eq!(
        dfa.find_leftmost_rev(&mut cache, b"abcxyz"),
        Err(MatchError::Quit { byte: b'x', offset: 3 })
    );

    Ok(())
}

// Tests that if we heuristically enable Unicode word boundaries but then
// instruct that a non-ASCII byte should NOT be a quit byte, then the builder
// will panic.
#[test]
#[should_panic]
fn quit_panics() {
    DFA::config().unicode_word_boundary(true).quit(b'\xFF', false);
}

// This tests an intesting case where even if the Unicode word boundary option
// is disabled, setting all non-ASCII bytes to be quit bytes will cause Unicode
// word boundaries to be enabled.
#[test]
fn unicode_word_implicitly_works() -> Result<(), Box<dyn Error>> {
    let mut config = DFA::config();
    for b in 0x80..=0xFF {
        config = config.quit(b, true);
    }
    let dfa = DFA::builder().configure(config).build(r"\b")?;
    let mut cache = dfa.create_cache();
    let expected = HalfMatch::must(0, 1);
    assert_eq!(dfa.find_leftmost_fwd(&mut cache, b" a"), Ok(Some(expected)));
    Ok(())
}

// Tests that we can provide a prefilter to a Regex, and the search reports
// correct results.
#[test]
fn prefilter_works() -> Result<(), Box<dyn Error>> {
    let mut re = Regex::new(r"a[0-9]+").unwrap();
    re.set_prefilter(Some(Box::new(SubstringPrefilter::new("a"))));
    let mut cache = re.create_cache();

    let text = b"foo abc foo a1a2a3 foo a123 bar aa456";
    let matches: Vec<(usize, usize)> = re
        .find_leftmost_iter(&mut cache, text)
        .map(|m| (m.start(), m.end()))
        .collect();
    assert_eq!(
        matches,
        vec![(12, 14), (14, 16), (16, 18), (23, 27), (33, 37),]
    );
    Ok(())
}

// This test confirms that a prefilter is active by using a prefilter that
// reports false negatives.
#[test]
fn prefilter_is_active() -> Result<(), Box<dyn Error>> {
    let text = b"za123";
    let mut re = Regex::new(r"a[0-9]+").unwrap();
    let mut cache = re.create_cache();

    re.set_prefilter(Some(Box::new(SubstringPrefilter::new("a"))));
    assert_eq!(
        re.find_leftmost(&mut cache, b"za123"),
        Some(MultiMatch::must(0, 1, 5))
    );
    assert_eq!(
        re.find_leftmost(&mut cache, b"a123"),
        Some(MultiMatch::must(0, 0, 4))
    );
    re.set_prefilter(Some(Box::new(BunkPrefilter::new())));
    assert_eq!(re.find_leftmost(&mut cache, b"za123"), None);
    // This checks that the prefilter is used when first starting the search,
    // instead of waiting until at least one transition has occurred.
    assert_eq!(re.find_leftmost(&mut cache, b"a123"), None);
    Ok(())
}