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Correctly handle nested or-patterns in exhaustiveness #117398

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Oct 30, 2023
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Correctly handle nested or-patterns in exhaustiveness #117398

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2 changes: 1 addition & 1 deletion compiler/rustc_mir_build/src/thir/pattern/usefulness.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -931,7 +931,7 @@ impl<'p, 'tcx> PatternColumn<'p, 'tcx> {
let specialized = pat.specialize(pcx, &ctor);
for (subpat, column) in specialized.iter().zip(&mut specialized_columns) {
if subpat.is_or_pat() {
column.patterns.extend(subpat.iter_fields())
column.patterns.extend(subpat.flatten_or_pat())
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It's kind of a shame that this code has an invariant (right?) that the | patterns must be flattened, but nothing protecting us against that in the first place.

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It is a shame indeed. I can see how I could encode it in the type system...

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I prefer not to actually. There are a lot of invariants in this file, this one is not one I'd rather spend my complexity budget on

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You got me thinking that I should really write down more of these invariants

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That would be awesome 😺

} else {
column.patterns.push(subpat)
}
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6 changes: 6 additions & 0 deletions tests/ui/or-patterns/exhaustiveness-pass.rs
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Expand Up @@ -35,4 +35,10 @@ fn main() {
((0, 0) | (1, 0),) => {}
_ => {}
}

// This one caused ICE https://github.com/rust-lang/rust/issues/117378
match (0u8, 0) {
(x @ 0 | x @ (1 | 2), _) => {}
(3.., _) => {}
}
}
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