diff options
| -rw-r--r-- | compiler/rustc_mir_build/src/build/matches/simplify.rs | 63 |
1 files changed, 41 insertions, 22 deletions
diff --git a/compiler/rustc_mir_build/src/build/matches/simplify.rs b/compiler/rustc_mir_build/src/build/matches/simplify.rs index c2e44a06321..8563c2d6dfb 100644 --- a/compiler/rustc_mir_build/src/build/matches/simplify.rs +++ b/compiler/rustc_mir_build/src/build/matches/simplify.rs @@ -38,16 +38,13 @@ impl<'a, 'tcx> Builder<'a, 'tcx> { &mut self, candidate: &mut Candidate<'pat, 'tcx>, ) -> bool { - // repeatedly simplify match pairs until fixed point is reached debug!("{candidate:#?}"); - - // existing_bindings and new_bindings exists to keep the semantics in order. + // `original_bindings` and `new_bindings` exist to keep the semantics in order. // Reversing the binding order for bindings after `@` changes the binding order in places - // it shouldn't be changed, for example `let (Some(a), Some(b)) = (x, y)` + // where it shouldn't be changed, for example `let (Some(a), Some(b)) = (x, y)`. // // To avoid this, the binding occurs in the following manner: - // * the bindings for one iteration of the following loop occurs in order (i.e. left to - // right) + // * the bindings for one iteration of the loop occurs in order (i.e. left to right) // * the bindings from the previous iteration of the loop is prepended to the bindings from // the current iteration (in the implementation this is done by mem::swap and extend) // * after all iterations, these new bindings are then appended to the bindings that were @@ -59,8 +56,40 @@ impl<'a, 'tcx> Builder<'a, 'tcx> { // binding in iter 2: [6, 7] // // final binding: [1, 2, 3, 6, 7, 4, 5] - let mut existing_bindings = mem::take(&mut candidate.bindings); + // + // This is because we treat refutable and irrefutable bindings differently. The binding + // order should be right-to-left if there are more _irrefutable_ bindings after `@` to + // please the borrow checker (#69971) + // Ex + // struct NonCopyStruct { + // copy_field: u32, + // } + // + // fn foo1(x: NonCopyStruct) { + // let y @ NonCopyStruct { copy_field: z } = x; + // // the above should turn into + // let z = x.copy_field; + // let y = x; + // } + // + // If however the bindings are refutable, i.e. under a test, then we keep the bindings + // left-to-right. + // Ex + // enum NonCopyEnum { + // Variant { copy_field: u32 }, + // None, + // } + // + // fn foo2(x: NonCopyEnum) { + // let y @ NonCopyEnum::Variant { copy_field: z } = x else { return }; + // // turns into + // let y = x; + // let z = (x as Variant).copy_field; + // // and raises an error + // } + let mut original_bindings = mem::take(&mut candidate.bindings); let mut new_bindings = Vec::new(); + // Repeatedly simplify match pairs until fixed point is reached loop { let mut changed = false; for match_pair in mem::take(&mut candidate.match_pairs) { @@ -74,19 +103,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> { } } - // Avoid issue #69971: the binding order should be right to left if there are more - // bindings after `@` to please the borrow checker - // Ex - // struct NonCopyStruct { - // copy_field: u32, - // } - // - // fn foo1(x: NonCopyStruct) { - // let y @ NonCopyStruct { copy_field: z } = x; - // // the above should turn into - // let z = x.copy_field; - // let y = x; - // } + // This does: new_bindings = candidate.bindings.take() ++ new_bindings candidate.bindings.extend_from_slice(&new_bindings); mem::swap(&mut candidate.bindings, &mut new_bindings); candidate.bindings.clear(); @@ -97,8 +114,10 @@ impl<'a, 'tcx> Builder<'a, 'tcx> { } } - existing_bindings.extend_from_slice(&new_bindings); - mem::swap(&mut candidate.bindings, &mut existing_bindings); + // Restore original bindings and append the new ones. + // This does: candidate.bindings = original_bindings ++ new_bindings + mem::swap(&mut candidate.bindings, &mut original_bindings); + candidate.bindings.extend_from_slice(&new_bindings); let did_expand_or = if let [MatchPair { pattern: Pat { kind: PatKind::Or { pats }, .. }, place }] = |