diff options
Diffstat (limited to 'compiler/rustc_trait_selection/src/traits/select/mod.rs')
| -rw-r--r-- | compiler/rustc_trait_selection/src/traits/select/mod.rs | 28 |
1 files changed, 11 insertions, 17 deletions
diff --git a/compiler/rustc_trait_selection/src/traits/select/mod.rs b/compiler/rustc_trait_selection/src/traits/select/mod.rs index 674ff30786b..956417b122c 100644 --- a/compiler/rustc_trait_selection/src/traits/select/mod.rs +++ b/compiler/rustc_trait_selection/src/traits/select/mod.rs @@ -1803,25 +1803,19 @@ impl<'tcx> SelectionContext<'_, 'tcx> { // 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() { + 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!(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. - 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 - // as they would otherwise overlap. - debug_assert_eq!(trivial_builtin.next(), None); - return Some(BuiltinCandidate { has_nested: false }); + // 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 @@ -1950,7 +1944,7 @@ 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 { - SizedCandidate + SizedCandidate { has_nested: _ } | BuiltinCandidate { has_nested: _ } | TransmutabilityCandidate | AutoImplCandidate |