diff options
Diffstat (limited to 'compiler/rustc_next_trait_solver/src')
| -rw-r--r-- | compiler/rustc_next_trait_solver/src/solve/assembly/mod.rs | 27 |
1 files changed, 24 insertions, 3 deletions
diff --git a/compiler/rustc_next_trait_solver/src/solve/assembly/mod.rs b/compiler/rustc_next_trait_solver/src/solve/assembly/mod.rs index b2d40146348..b75da23cdac 100644 --- a/compiler/rustc_next_trait_solver/src/solve/assembly/mod.rs +++ b/compiler/rustc_next_trait_solver/src/solve/assembly/mod.rs @@ -21,7 +21,7 @@ use crate::delegate::SolverDelegate; use crate::solve::inspect::ProbeKind; use crate::solve::{ BuiltinImplSource, CandidateSource, CanonicalResponse, Certainty, EvalCtxt, Goal, GoalSource, - MaybeCause, NoSolution, ParamEnvSource, QueryResult, + MaybeCause, NoSolution, ParamEnvSource, QueryResult, has_no_inference_or_external_constraints, }; enum AliasBoundKind { @@ -395,9 +395,30 @@ where match assemble_from { AssembleCandidatesFrom::All => { - self.assemble_impl_candidates(goal, &mut candidates); self.assemble_builtin_impl_candidates(goal, &mut candidates); - self.assemble_object_bound_candidates(goal, &mut candidates); + // For performance we only assemble impls if there are no candidates + // which would shadow them. This is necessary to avoid hangs in rayon, + // see trait-system-refactor-initiative#109 for more details. + // + // We always assemble builtin impls as trivial builtin impls have a higher + // priority than where-clauses. + // + // We only do this if any such candidate applies without any constraints + // as we may want to weaken inference guidance in the future and don't want + // to worry about causing major performance regressions when doing so. + // See trait-system-refactor-initiative#226 for some ideas here. + if TypingMode::Coherence == self.typing_mode() + || !candidates.iter().any(|c| { + matches!( + c.source, + CandidateSource::ParamEnv(ParamEnvSource::NonGlobal) + | CandidateSource::AliasBound + ) && has_no_inference_or_external_constraints(c.result) + }) + { + self.assemble_impl_candidates(goal, &mut candidates); + self.assemble_object_bound_candidates(goal, &mut candidates); + } } AssembleCandidatesFrom::EnvAndBounds => {} } |