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Rollup merge of #127707 - Zalathar:expand-until, r=Nadrieril

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match lowering: Use an iterator to find `expand_until`

A small cleanup that I noticed while looking at #127164.

This makes it easier to see that the split point is always the index after the found item, or the whole list if no stopping point was found.

r? `@Nadrieril`
This commit is contained in:
Matthias Krüger 2024-07-16 18:09:09 +02:00 committed by GitHub
commit 7409a5281d
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1 changed files with 19 additions and 14 deletions
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33
compiler/rustc_mir_build/src/build/matches/mod.rs
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@ -1547,10 +1547,13 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
start_block: BasicBlock,
candidates: &'b mut [&'c mut Candidate<'pat, 'tcx>],
) -> BlockAnd<&'b mut [&'c mut Candidate<'pat, 'tcx>]> {
// We can't expand or-patterns freely. The rule is: if the candidate has an
// or-pattern as its only remaining match pair, we can expand it freely. If it has
// other match pairs, we can expand it but we can't process more candidates after
// it.
// We can't expand or-patterns freely. The rule is:
// - If a candidate doesn't start with an or-pattern, we include it in
// the expansion list as-is (i.e. it "expands" to itself).
// - If a candidate has an or-pattern as its only remaining match pair,
// we can expand it.
// - If it starts with an or-pattern but also has other match pairs,
// we can expand it, but we can't process more candidates after it.
//
// If we didn't stop, the `otherwise` cases could get mixed up. E.g. in the
// following, or-pattern simplification (in `merge_trivial_subcandidates`) makes it
@ -1567,17 +1570,17 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
// }
// ```
//
// We therefore split the `candidates` slice in two, expand or-patterns in the first half,
// We therefore split the `candidates` slice in two, expand or-patterns in the first part,
// and process the rest separately.
let mut expand_until = 0;
for (i, candidate) in candidates.iter().enumerate() {
expand_until = i + 1;
if candidate.match_pairs.len() > 1 && candidate.starts_with_or_pattern() {
// The candidate has an or-pattern as well as more match pairs: we must
// split the candidates list here.
break;
}
}
let expand_until = candidates
.iter()
.position(|candidate| {
// If a candidate starts with an or-pattern and has more match pairs,
// we can expand it, but we must stop expanding _after_ it.
candidate.match_pairs.len() > 1 && candidate.starts_with_or_pattern()
})
.map(|pos| pos + 1) // Stop _after_ the found candidate
.unwrap_or(candidates.len()); // Otherwise, include all candidates
let (candidates_to_expand, remaining_candidates) = candidates.split_at_mut(expand_until);
// Expand one level of or-patterns for each candidate in `candidates_to_expand`.
@ -1592,6 +1595,8 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
expanded_candidates.push(subcandidate);
}
} else {
// A candidate that doesn't start with an or-pattern has nothing to
// expand, so it is included in the post-expansion list as-is.
expanded_candidates.push(candidate);
}
}