diff options
4 files changed, 41 insertions, 6 deletions
diff --git a/compiler/rustc_middle/src/traits/select.rs b/compiler/rustc_middle/src/traits/select.rs index 811bd8fb458..749f3c31bf8 100644 --- a/compiler/rustc_middle/src/traits/select.rs +++ b/compiler/rustc_middle/src/traits/select.rs @@ -95,10 +95,13 @@ pub type EvaluationCache<'tcx, ENV> = Cache<(ENV, ty::PolyTraitPredicate<'tcx>), /// parameter environment. #[derive(PartialEq, Eq, Debug, Clone, TypeVisitable)] pub enum SelectionCandidate<'tcx> { + /// UwU + SizedCandidate, + /// A builtin implementation for some specific traits, used in cases /// where we cannot rely an ordinary library implementations. /// - /// The most notable examples are `sized`, `Copy` and `Clone`. This is also + /// The most notable examples are `Copy` and `Clone`. This is also /// used for the `DiscriminantKind` and `Pointee` trait, both of which have /// an associated type. BuiltinCandidate { 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 a8d8003ead6..9c0efec2e6c 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) { @@ -1059,6 +1056,25 @@ 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(_) => { + candidates.vec.push(SizedCandidate); + } + 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 4cd6781ab89..349eab2cbe3 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 => { + let data = self.confirm_builtin_candidate(obligation, true); + 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 e1adabbeaa6..674ff30786b 100644 --- a/compiler/rustc_trait_selection/src/traits/select/mod.rs +++ b/compiler/rustc_trait_selection/src/traits/select/mod.rs @@ -1801,6 +1801,16 @@ impl<'tcx> SelectionContext<'_, 'tcx> { return Some(candidates.pop().unwrap().candidate); } + // We prefer `Sized` candidates over everything. + let mut sized_candidates = + candidates.iter().filter(|c| matches!(c.candidate, SizedCandidate)); + 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!(sized_candidates.next(), None); + return Some(SizedCandidate); + } + // 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. @@ -1940,7 +1950,8 @@ 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 + | BuiltinCandidate { has_nested: _ } | TransmutabilityCandidate | AutoImplCandidate | ClosureCandidate { .. } |