diff options
| -rw-r--r-- | compiler/rustc_next_trait_solver/src/solve/assembly/mod.rs | 27 | ||||
| -rw-r--r-- | tests/ui/traits/next-solver/cycles/rayon-hang-1.rs | 32 | ||||
| -rw-r--r-- | tests/ui/traits/next-solver/cycles/rayon-hang-2.rs | 49 |
3 files changed, 105 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 => {} } diff --git a/tests/ui/traits/next-solver/cycles/rayon-hang-1.rs b/tests/ui/traits/next-solver/cycles/rayon-hang-1.rs new file mode 100644 index 00000000000..61e1f1b200f --- /dev/null +++ b/tests/ui/traits/next-solver/cycles/rayon-hang-1.rs @@ -0,0 +1,32 @@ +//@ compile-flags: -Znext-solver +//@ check-pass + +// A regression test for trait-system-refactor-initiative#109. + +trait ParallelIterator: Sized { + type Item; +} +trait IntoParallelIterator { + type Iter: ParallelIterator<Item = Self::Item>; + type Item; +} +impl<T: ParallelIterator> IntoParallelIterator for T { + type Iter = T; + type Item = T::Item; +} + +macro_rules! multizip_impls { + ($($T:ident),+) => { + fn foo<$( $T, )+>() where + $( + $T: IntoParallelIterator, + $T::Iter: ParallelIterator, + )+ + ($( $T, )+): IntoParallelIterator<Item = ($( $T::Item, )+)>, + {} + } +} + +multizip_impls! { A, B, C, D, E, F, G, H, I, J, K, L } + +fn main() {} diff --git a/tests/ui/traits/next-solver/cycles/rayon-hang-2.rs b/tests/ui/traits/next-solver/cycles/rayon-hang-2.rs new file mode 100644 index 00000000000..bb5d8335dd6 --- /dev/null +++ b/tests/ui/traits/next-solver/cycles/rayon-hang-2.rs @@ -0,0 +1,49 @@ +//@ compile-flags: -Znext-solver +//@ check-pass + +// A regression test for trait-system-refactor-initiative#109. +// Unlike `rayon-hang-1.rs` the cycles in this test are not +// unproductive, which causes the `AliasRelate` goal when trying +// to apply where-clauses to only error in the second iteration. +// +// This makes the exponential blowup to be significantly harder +// to avoid. + +trait ParallelIterator: Sized { + type Item; +} + +trait IntoParallelIteratorIndir { + type Iter: ParallelIterator<Item = Self::Item>; + type Item; +} +impl<I> IntoParallelIteratorIndir for I +where + Box<I>: IntoParallelIterator, +{ + type Iter = <Box<I> as IntoParallelIterator>::Iter; + type Item = <Box<I> as IntoParallelIterator>::Item; +} +trait IntoParallelIterator { + type Iter: ParallelIterator<Item = Self::Item>; + type Item; +} +impl<T: ParallelIterator> IntoParallelIterator for T { + type Iter = T; + type Item = T::Item; +} + +macro_rules! multizip_impls { + ($($T:ident),+) => { + fn foo<'a, $( $T, )+>() where + $( + $T: IntoParallelIteratorIndir, + $T::Iter: ParallelIterator, + )+ + {} + } +} + +multizip_impls! { A, B, C, D, E, F, G, H, I, J, K, L } + +fn main() {} |