diff options
| -rw-r--r-- | compiler/rustc_hir_typeck/src/pat.rs | 25 |
1 files changed, 13 insertions, 12 deletions
diff --git a/compiler/rustc_hir_typeck/src/pat.rs b/compiler/rustc_hir_typeck/src/pat.rs index 5e6cca51c92..391acce97bd 100644 --- a/compiler/rustc_hir_typeck/src/pat.rs +++ b/compiler/rustc_hir_typeck/src/pat.rs @@ -168,15 +168,16 @@ enum AdjustMode { Pass, } -/// `ref mut` patterns (explicit or match-ergonomics) -/// are not allowed behind an `&` reference. +/// `ref mut` bindings (explicit or match-ergonomics) are not allowed behind an `&` reference. +/// Normally, the borrow checker enforces this, but for (currently experimental) match ergonomics, +/// we track this when typing patterns for two purposes: /// -/// This includes explicit `ref mut` behind `&` patterns -/// that match against `&mut` references, -/// where the code would have compiled -/// had the pattern been written as `&mut`. -/// However, the borrow checker will not catch -/// this last case, so we need to throw an error ourselves. +/// - For RFC 3627's Rule 3, when this would prevent us from binding with `ref mut`, we limit the +/// default binding mode to be by shared `ref` when it would otherwise be `ref mut`. +/// +/// - For RFC 3627's Rule 5, we allow `&` patterns to match against `&mut` references, treating them +/// as if they were shared references. Since the scrutinee is mutable in this case, the borrow +/// checker won't catch if we bind with `ref mut`, so we need to throw an error ourselves. #[derive(Clone, Copy, Debug, PartialEq, Eq)] enum MutblCap { /// Mutability restricted to immutable. @@ -477,9 +478,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> { if features.ref_pat_eat_one_layer_2024() || features.ref_pat_eat_one_layer_2024_structural() { def_br = def_br.cap_ref_mutability(max_ref_mutbl.as_mutbl()); - if def_br == ByRef::Yes(Mutability::Not) { - max_ref_mutbl = MutblCap::Not; - } + } + if def_br == ByRef::Yes(Mutability::Not) { + max_ref_mutbl = MutblCap::Not; } if !pat_adjustments.is_empty() { @@ -2292,7 +2293,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> { if (no_ref_mut_behind_and && r_mutbl >= pat_mutbl) || r_mutbl == pat_mutbl => { - if no_ref_mut_behind_and && r_mutbl == Mutability::Not { + if r_mutbl == Mutability::Not { pat_info.max_ref_mutbl = MutblCap::Not; } |