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always peel &mut, to allow matching on &mut str

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dianne
2025-05-05 03:40:37 -07:00
parent fe98130e0f
commit 17bb4bbc86
8 changed files with 153 additions and 6 deletions
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13
compiler/rustc_hir_typeck/src/pat.rs
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@@ -740,10 +740,17 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
);
// If the pattern has as many or more layers of reference as the expected type, we can match
// without peeling more, *unless* we find a smart pointer that we also need to peel.
// TODO: always peel `&mut`
// without peeling more, unless we find a smart pointer or `&mut` that we also need to peel.
// We don't treat `&` and `&mut` as interchangeable, but by peeling `&mut`s before matching,
// we can still, e.g., match on a `&mut str` with a string literal pattern. This is because
// string literal patterns may be used where `str` is expected.
let mut expected_ref_layers = 0;
while let ty::Ref(_, inner_ty, _) = *expected.kind() {
while let ty::Ref(_, inner_ty, mutbl) = *expected.kind() {
if mutbl.is_mut() {
// Mutable references can't be in the final value of constants, thus they can't be
// at the head of their types, thus we should always peel `&mut`.
return true;
}
expected_ref_layers += 1;
expected = inner_ty;
}