diff options
Diffstat (limited to 'compiler')
4 files changed, 58 insertions, 39 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 83b2465d05a..ecb57cc0ad7 100644 --- a/compiler/rustc_next_trait_solver/src/solve/assembly/mod.rs +++ b/compiler/rustc_next_trait_solver/src/solve/assembly/mod.rs @@ -288,6 +288,21 @@ where ) -> Vec<Candidate<I>>; } +/// Allows callers of `assemble_and_evaluate_candidates` to choose whether to limit +/// candidate assembly to param-env and alias-bound candidates. +/// +/// On top of being a micro-optimization, as it avoids doing unnecessary work when +/// a param-env trait bound candidate shadows impls for normalization, this is also +/// required to prevent query cycles due to RPITIT inference. See the issue at: +/// <https://github.com/rust-lang/trait-system-refactor-initiative/issues/173>. +pub(super) enum AssembleCandidatesFrom { + All, + /// Only assemble candidates from the environment and alias bounds, ignoring + /// user-written and built-in impls. We only expect `ParamEnv` and `AliasBound` + /// candidates to be assembled. + EnvAndBounds, +} + impl<D, I> EvalCtxt<'_, D> where D: SolverDelegate<Interner = I>, @@ -296,6 +311,7 @@ where pub(super) fn assemble_and_evaluate_candidates<G: GoalKind<D>>( &mut self, goal: Goal<I, G>, + assemble_from: AssembleCandidatesFrom, ) -> Vec<Candidate<I>> { let Ok(normalized_self_ty) = self.structurally_normalize_ty(goal.param_env, goal.predicate.self_ty()) @@ -322,16 +338,18 @@ where } } - self.assemble_impl_candidates(goal, &mut candidates); - - self.assemble_builtin_impl_candidates(goal, &mut candidates); - self.assemble_alias_bound_candidates(goal, &mut candidates); - - self.assemble_object_bound_candidates(goal, &mut candidates); - self.assemble_param_env_candidates(goal, &mut candidates); + 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); + } + AssembleCandidatesFrom::EnvAndBounds => {} + } + candidates } @@ -754,6 +772,9 @@ where }) } + /// Assemble and merge candidates for goals which are related to an underlying trait + /// goal. Right now, this is normalizes-to and host effect goals. + /// /// We sadly can't simply take all possible candidates for normalization goals /// and check whether they result in the same constraints. We want to make sure /// that trying to normalize an alias doesn't result in constraints which aren't @@ -782,47 +803,44 @@ where /// /// See trait-system-refactor-initiative#124 for more details. #[instrument(level = "debug", skip(self, inject_normalize_to_rigid_candidate), ret)] - pub(super) fn merge_candidates( + pub(super) fn assemble_and_merge_candidates<G: GoalKind<D>>( &mut self, proven_via: Option<TraitGoalProvenVia>, - candidates: Vec<Candidate<I>>, + goal: Goal<I, G>, inject_normalize_to_rigid_candidate: impl FnOnce(&mut EvalCtxt<'_, D>) -> QueryResult<I>, ) -> QueryResult<I> { let Some(proven_via) = proven_via else { // We don't care about overflow. If proving the trait goal overflowed, then // it's enough to report an overflow error for that, we don't also have to // overflow during normalization. - return Ok(self.make_ambiguous_response_no_constraints(MaybeCause::Ambiguity)); + // + // We use `forced_ambiguity` here over `make_ambiguous_response_no_constraints` + // because the former will also record a built-in candidate in the inspector. + return self.forced_ambiguity(MaybeCause::Ambiguity).map(|cand| cand.result); }; match proven_via { TraitGoalProvenVia::ParamEnv | TraitGoalProvenVia::AliasBound => { - let mut considered_candidates = Vec::new(); - considered_candidates.extend( - candidates - .iter() - .filter(|c| matches!(c.source, CandidateSource::ParamEnv(_))) - .map(|c| c.result), - ); - // Even when a trait bound has been proven using a where-bound, we // still need to consider alias-bounds for normalization, see - // tests/ui/next-solver/alias-bound-shadowed-by-env.rs. - // + // `tests/ui/next-solver/alias-bound-shadowed-by-env.rs`. + let candidates_from_env_and_bounds: Vec<_> = self + .assemble_and_evaluate_candidates(goal, AssembleCandidatesFrom::EnvAndBounds); + // We still need to prefer where-bounds over alias-bounds however. - // See tests/ui/winnowing/norm-where-bound-gt-alias-bound.rs. - // - // FIXME(const_trait_impl): should this behavior also be used by - // constness checking. Doing so is *at least theoretically* breaking, - // see github.com/rust-lang/rust/issues/133044#issuecomment-2500709754 - if considered_candidates.is_empty() { - considered_candidates.extend( - candidates - .iter() - .filter(|c| matches!(c.source, CandidateSource::AliasBound)) - .map(|c| c.result), - ); - } + // See `tests/ui/winnowing/norm-where-bound-gt-alias-bound.rs`. + let mut considered_candidates: Vec<_> = if candidates_from_env_and_bounds + .iter() + .any(|c| matches!(c.source, CandidateSource::ParamEnv(_))) + { + candidates_from_env_and_bounds + .into_iter() + .filter(|c| matches!(c.source, CandidateSource::ParamEnv(_))) + .map(|c| c.result) + .collect() + } else { + candidates_from_env_and_bounds.into_iter().map(|c| c.result).collect() + }; // If the trait goal has been proven by using the environment, we want to treat // aliases as rigid if there are no applicable projection bounds in the environment. @@ -839,6 +857,9 @@ where } } TraitGoalProvenVia::Misc => { + let candidates = + self.assemble_and_evaluate_candidates(goal, AssembleCandidatesFrom::All); + // Prefer "orphaned" param-env normalization predicates, which are used // (for example, and ideally only) when proving item bounds for an impl. let candidates_from_env: Vec<_> = candidates diff --git a/compiler/rustc_next_trait_solver/src/solve/effect_goals.rs b/compiler/rustc_next_trait_solver/src/solve/effect_goals.rs index 0b61c368d8e..7752a705cd1 100644 --- a/compiler/rustc_next_trait_solver/src/solve/effect_goals.rs +++ b/compiler/rustc_next_trait_solver/src/solve/effect_goals.rs @@ -399,12 +399,11 @@ where &mut self, goal: Goal<I, ty::HostEffectPredicate<I>>, ) -> QueryResult<I> { - let candidates = self.assemble_and_evaluate_candidates(goal); let (_, proven_via) = self.probe(|_| ProbeKind::ShadowedEnvProbing).enter(|ecx| { let trait_goal: Goal<I, ty::TraitPredicate<I>> = goal.with(ecx.cx(), goal.predicate.trait_ref); ecx.compute_trait_goal(trait_goal) })?; - self.merge_candidates(proven_via, candidates, |_ecx| Err(NoSolution)) + self.assemble_and_merge_candidates(proven_via, goal, |_ecx| Err(NoSolution)) } } diff --git a/compiler/rustc_next_trait_solver/src/solve/normalizes_to/mod.rs b/compiler/rustc_next_trait_solver/src/solve/normalizes_to/mod.rs index fdeb276a58e..9466901683e 100644 --- a/compiler/rustc_next_trait_solver/src/solve/normalizes_to/mod.rs +++ b/compiler/rustc_next_trait_solver/src/solve/normalizes_to/mod.rs @@ -32,14 +32,13 @@ where let cx = self.cx(); match goal.predicate.alias.kind(cx) { ty::AliasTermKind::ProjectionTy | ty::AliasTermKind::ProjectionConst => { - let candidates = self.assemble_and_evaluate_candidates(goal); let trait_ref = goal.predicate.alias.trait_ref(cx); let (_, proven_via) = self.probe(|_| ProbeKind::ShadowedEnvProbing).enter(|ecx| { let trait_goal: Goal<I, ty::TraitPredicate<I>> = goal.with(cx, trait_ref); ecx.compute_trait_goal(trait_goal) })?; - self.merge_candidates(proven_via, candidates, |ecx| { + self.assemble_and_merge_candidates(proven_via, goal, |ecx| { ecx.probe(|&result| ProbeKind::RigidAlias { result }).enter(|this| { this.structurally_instantiate_normalizes_to_term( goal, diff --git a/compiler/rustc_next_trait_solver/src/solve/trait_goals.rs b/compiler/rustc_next_trait_solver/src/solve/trait_goals.rs index 409af8568d7..7bd1300f34e 100644 --- a/compiler/rustc_next_trait_solver/src/solve/trait_goals.rs +++ b/compiler/rustc_next_trait_solver/src/solve/trait_goals.rs @@ -13,7 +13,7 @@ use tracing::{instrument, trace}; use crate::delegate::SolverDelegate; use crate::solve::assembly::structural_traits::{self, AsyncCallableRelevantTypes}; -use crate::solve::assembly::{self, Candidate}; +use crate::solve::assembly::{self, AssembleCandidatesFrom, Candidate}; use crate::solve::inspect::ProbeKind; use crate::solve::{ BuiltinImplSource, CandidateSource, Certainty, EvalCtxt, Goal, GoalSource, MaybeCause, @@ -1365,7 +1365,7 @@ where &mut self, goal: Goal<I, TraitPredicate<I>>, ) -> Result<(CanonicalResponse<I>, Option<TraitGoalProvenVia>), NoSolution> { - let candidates = self.assemble_and_evaluate_candidates(goal); + let candidates = self.assemble_and_evaluate_candidates(goal, AssembleCandidatesFrom::All); self.merge_trait_candidates(goal, candidates) } } |