diff options
Diffstat (limited to 'compiler/rustc_trait_selection')
3 files changed, 43 insertions, 15 deletions
diff --git a/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs b/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs index 4cfd8149b1e..d15c9afef3a 100644 --- a/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs +++ b/compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs @@ -86,10 +86,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> { // `Pointee` is automatically implemented for every type. candidates.vec.push(BuiltinCandidate { has_nested: false }); } else if tcx.is_lang_item(def_id, LangItem::Sized) { - // Sized is never implementable by end-users, it is - // always automatically computed. - let sized_conditions = self.sized_conditions(obligation); - self.assemble_builtin_bound_candidates(sized_conditions, &mut candidates); + self.assemble_builtin_sized_candidate(obligation, &mut candidates); } else if tcx.is_lang_item(def_id, LangItem::Unsize) { self.assemble_candidates_for_unsizing(obligation, &mut candidates); } else if tcx.is_lang_item(def_id, LangItem::Destruct) { @@ -1061,6 +1058,27 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> { /// Assembles the trait which are built-in to the language itself: /// `Copy`, `Clone` and `Sized`. #[instrument(level = "debug", skip(self, candidates))] + fn assemble_builtin_sized_candidate( + &mut self, + obligation: &PolyTraitObligation<'tcx>, + candidates: &mut SelectionCandidateSet<'tcx>, + ) { + match self.sized_conditions(obligation) { + BuiltinImplConditions::Where(nested) => { + candidates + .vec + .push(SizedCandidate { has_nested: !nested.skip_binder().is_empty() }); + } + BuiltinImplConditions::None => {} + BuiltinImplConditions::Ambiguous => { + candidates.ambiguous = true; + } + } + } + + /// Assembles the trait which are built-in to the language itself: + /// e.g. `Copy` and `Clone`. + #[instrument(level = "debug", skip(self, candidates))] fn assemble_builtin_bound_candidates( &mut self, conditions: BuiltinImplConditions<'tcx>, diff --git a/compiler/rustc_trait_selection/src/traits/select/confirmation.rs b/compiler/rustc_trait_selection/src/traits/select/confirmation.rs index a66c958c109..630241725fd 100644 --- a/compiler/rustc_trait_selection/src/traits/select/confirmation.rs +++ b/compiler/rustc_trait_selection/src/traits/select/confirmation.rs @@ -40,6 +40,11 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> { candidate: SelectionCandidate<'tcx>, ) -> Result<Selection<'tcx>, SelectionError<'tcx>> { let mut impl_src = match candidate { + SizedCandidate { has_nested } => { + let data = self.confirm_builtin_candidate(obligation, has_nested); + ImplSource::Builtin(BuiltinImplSource::Misc, data) + } + BuiltinCandidate { has_nested } => { let data = self.confirm_builtin_candidate(obligation, has_nested); ImplSource::Builtin(BuiltinImplSource::Misc, data) diff --git a/compiler/rustc_trait_selection/src/traits/select/mod.rs b/compiler/rustc_trait_selection/src/traits/select/mod.rs index e439df76cd4..0679dbf1296 100644 --- a/compiler/rustc_trait_selection/src/traits/select/mod.rs +++ b/compiler/rustc_trait_selection/src/traits/select/mod.rs @@ -1801,17 +1801,21 @@ impl<'tcx> SelectionContext<'_, 'tcx> { return Some(candidates.pop().unwrap().candidate); } - // We prefer trivial builtin candidates, i.e. builtin impls without any nested - // requirements, over all others. This is a fix for #53123 and prevents winnowing - // from accidentally extending the lifetime of a variable. - let mut trivial_builtin = candidates - .iter() - .filter(|c| matches!(c.candidate, BuiltinCandidate { has_nested: false })); - if let Some(_trivial) = trivial_builtin.next() { - // There should only ever be a single trivial builtin candidate + // We prefer `Sized` candidates over everything. + let mut sized_candidates = + candidates.iter().filter(|c| matches!(c.candidate, SizedCandidate { has_nested: _ })); + if let Some(sized_candidate) = sized_candidates.next() { + // There should only ever be a single sized candidate // as they would otherwise overlap. - debug_assert_eq!(trivial_builtin.next(), None); - return Some(BuiltinCandidate { has_nested: false }); + debug_assert_eq!(sized_candidates.next(), None); + // Only prefer the built-in `Sized` candidate if its nested goals are certain. + // Otherwise, we may encounter failure later on if inference causes this candidate + // to not hold, but a where clause would've applied instead. + if sized_candidate.evaluation.must_apply_modulo_regions() { + return Some(sized_candidate.candidate.clone()); + } else { + return None; + } } // Before we consider where-bounds, we have to deduplicate them here and also @@ -1940,7 +1944,8 @@ impl<'tcx> SelectionContext<'_, 'tcx> { // Don't use impl candidates which overlap with other candidates. // This should pretty much only ever happen with malformed impls. if candidates.iter().all(|c| match c.candidate { - BuiltinCandidate { has_nested: _ } + SizedCandidate { has_nested: _ } + | BuiltinCandidate { has_nested: _ } | TransmutabilityCandidate | AutoImplCandidate | ClosureCandidate { .. } |