diff options
Diffstat (limited to 'compiler')
| -rw-r--r-- | compiler/rustc_hir_typeck/src/pat.rs | 89 |
1 files changed, 67 insertions, 22 deletions
diff --git a/compiler/rustc_hir_typeck/src/pat.rs b/compiler/rustc_hir_typeck/src/pat.rs index ea335c7a4a7..c96ad0749a1 100644 --- a/compiler/rustc_hir_typeck/src/pat.rs +++ b/compiler/rustc_hir_typeck/src/pat.rs @@ -177,16 +177,20 @@ enum PeelKind { /// Only peel reference types. This is used for explicit `deref!(_)` patterns, which dereference /// any number of `&`/`&mut` references, plus a single smart pointer. ExplicitDerefPat, - /// Implicitly peel any number of references, and if `deref_patterns` is enabled, smart pointer - /// ADTs. In order to peel only as much as necessary for the pattern to match, the `until_adt` - /// field contains the ADT def that the pattern is a constructor for, if applicable, so that we - /// don't peel it. See [`ResolvedPat`] for more information. - Implicit { until_adt: Option<DefId> }, + /// Implicitly peel references, and if `deref_patterns` is enabled, smart pointer ADTs. + Implicit { + /// The ADT the pattern is a constructor for, if applicable, so that we don't peel it. See + /// [`ResolvedPat`] for more information. + until_adt: Option<DefId>, + /// The number of references at the head of the pattern's type, so we can leave that many + /// untouched. This is `1` for string literals, and `0` for most patterns. + pat_ref_layers: usize, + }, } impl AdjustMode { const fn peel_until_adt(opt_adt_def: Option<DefId>) -> AdjustMode { - AdjustMode::Peel { kind: PeelKind::Implicit { until_adt: opt_adt_def } } + AdjustMode::Peel { kind: PeelKind::Implicit { until_adt: opt_adt_def, pat_ref_layers: 0 } } } const fn peel_all() -> AdjustMode { AdjustMode::peel_until_adt(None) @@ -488,9 +492,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> { match pat.kind { // Peel off a `&` or `&mut` from the scrutinee type. See the examples in // `tests/ui/rfcs/rfc-2005-default-binding-mode`. - _ if let AdjustMode::Peel { .. } = adjust_mode + _ if let AdjustMode::Peel { kind: peel_kind } = adjust_mode && pat.default_binding_modes - && let ty::Ref(_, inner_ty, inner_mutability) = *expected.kind() => + && let ty::Ref(_, inner_ty, inner_mutability) = *expected.kind() + && self.should_peel_ref(peel_kind, expected) => { debug!("inspecting {:?}", expected); @@ -665,21 +670,32 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> { // String and byte-string literals result in types `&str` and `&[u8]` respectively. // All other literals result in non-reference types. - // As a result, we allow `if let 0 = &&0 {}` but not `if let "foo" = &&"foo" {}`. - // - // Call `resolve_vars_if_possible` here for inline const blocks. - PatKind::Expr(lt) => match self.resolve_vars_if_possible(self.check_pat_expr_unadjusted(lt)).kind() { - ty::Ref(..) => AdjustMode::Pass, - _ => { - // Path patterns have already been handled, and inline const blocks currently - // aren't possible to write, so any handling for them would be untested. - if cfg!(debug_assertions) - && self.tcx.features().deref_patterns() - && !matches!(lt.kind, PatExprKind::Lit { .. }) - { - span_bug!(lt.span, "FIXME(deref_patterns): adjust mode unimplemented for {:?}", lt.kind); + // As a result, we allow `if let 0 = &&0 {}` but not `if let "foo" = &&"foo" {}` unless + // `deref_patterns` is enabled. + PatKind::Expr(lt) => { + // Path patterns have already been handled, and inline const blocks currently + // aren't possible to write, so any handling for them would be untested. + if cfg!(debug_assertions) + && self.tcx.features().deref_patterns() + && !matches!(lt.kind, PatExprKind::Lit { .. }) + { + span_bug!(lt.span, "FIXME(deref_patterns): adjust mode unimplemented for {:?}", lt.kind); + } + // Call `resolve_vars_if_possible` here for inline const blocks. + let lit_ty = self.resolve_vars_if_possible(self.check_pat_expr_unadjusted(lt)); + // If `deref_patterns` is enabled, allow `if let "foo" = &&"foo" {}`. + if self.tcx.features().deref_patterns() { + let mut peeled_ty = lit_ty; + let mut pat_ref_layers = 0; + while let ty::Ref(_, inner_ty, mutbl) = *peeled_ty.kind() { + // We rely on references at the head of constants being immutable. + debug_assert!(mutbl.is_not()); + pat_ref_layers += 1; + peeled_ty = inner_ty; } - AdjustMode::peel_all() + AdjustMode::Peel { kind: PeelKind::Implicit { until_adt: None, pat_ref_layers } } + } else { + if lit_ty.is_ref() { AdjustMode::Pass } else { AdjustMode::peel_all() } } }, @@ -705,6 +721,35 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> { } } + /// Assuming `expected` is a reference type, determine whether to peel it before matching. + fn should_peel_ref(&self, peel_kind: PeelKind, mut expected: Ty<'tcx>) -> bool { + debug_assert!(expected.is_ref()); + let pat_ref_layers = match peel_kind { + PeelKind::ExplicitDerefPat => 0, + PeelKind::Implicit { pat_ref_layers, .. } => pat_ref_layers, + }; + + // Most patterns don't have reference types, so we'll want to peel all references from the + // scrutinee before matching. To optimize for the common case, return early. + if pat_ref_layers == 0 { + return true; + } + debug_assert!( + self.tcx.features().deref_patterns(), + "Peeling for patterns with reference types is gated by `deref_patterns`." + ); + + // 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` + let mut expected_ref_layers = 0; + while let ty::Ref(_, inner_ty, _) = *expected.kind() { + expected_ref_layers += 1; + expected = inner_ty; + } + pat_ref_layers < expected_ref_layers || self.should_peel_smart_pointer(peel_kind, expected) + } + /// Determine whether `expected` is a smart pointer type that should be peeled before matching. fn should_peel_smart_pointer(&self, peel_kind: PeelKind, expected: Ty<'tcx>) -> bool { // Explicit `deref!(_)` patterns match against smart pointers; don't peel in that case. |