diff options
Diffstat (limited to 'compiler')
| -rw-r--r-- | compiler/rustc_trait_selection/src/traits/select/mod.rs | 76 |
1 files changed, 62 insertions, 14 deletions
diff --git a/compiler/rustc_trait_selection/src/traits/select/mod.rs b/compiler/rustc_trait_selection/src/traits/select/mod.rs index 3fbe8e39d1e..926044bd6a8 100644 --- a/compiler/rustc_trait_selection/src/traits/select/mod.rs +++ b/compiler/rustc_trait_selection/src/traits/select/mod.rs @@ -60,6 +60,20 @@ use rustc_middle::ty::print::with_no_trimmed_paths; mod candidate_assembly; mod confirmation; +/// Whether to consider the binder of higher ranked goals for the `leak_check` when +/// evaluating higher-ranked goals. See #119820 for more info. +/// +/// While this is a bit hacky, it is necessary to match the behavior of the new solver: +/// We eagerly instantiate binders in the new solver, outside of candidate selection, so +/// the leak check inside of candidates does not consider any bound vars from the higher +/// ranked goal. However, we do exit the binder once we're completely finished with a goal, +/// so the leak-check can be used in evaluate by causing nested higher-ranked goals to fail. +#[derive(Debug, Copy, Clone)] +enum LeakCheckHigherRankedGoal { + No, + Yes, +} + #[derive(Clone, Debug, Eq, PartialEq, Hash)] pub enum IntercrateAmbiguityCause<'tcx> { DownstreamCrate { trait_ref: ty::TraitRef<'tcx>, self_ty: Option<Ty<'tcx>> }, @@ -384,7 +398,10 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> { let mut no_candidates_apply = true; for c in candidate_set.vec.iter() { - if self.evaluate_candidate(stack, c)?.may_apply() { + if self + .evaluate_candidate(stack, c, LeakCheckHigherRankedGoal::No)? + .may_apply() + { no_candidates_apply = false; break; } @@ -455,7 +472,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> { // is needed for specialization. Propagate overflow if it occurs. let mut candidates = candidates .into_iter() - .map(|c| match self.evaluate_candidate(stack, &c) { + .map(|c| match self.evaluate_candidate(stack, &c, LeakCheckHigherRankedGoal::No) { Ok(eval) if eval.may_apply() => { Ok(Some(EvaluatedCandidate { candidate: c, evaluation: eval })) } @@ -545,7 +562,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> { obligation: &PredicateObligation<'tcx>, ) -> Result<EvaluationResult, OverflowError> { debug_assert!(!self.infcx.next_trait_solver()); - self.evaluation_probe(|this| { + self.evaluation_probe(|this, _outer_universe| { let goal = this.infcx.resolve_vars_if_possible((obligation.predicate, obligation.param_env)); let mut result = this.evaluate_predicate_recursively( @@ -561,13 +578,18 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> { }) } + /// Computes the evaluation result of `op`, discarding any constraints. + /// + /// This also runs for leak check to allow higher ranked region errors to impact + /// selection. By default it checks for leaks from all universes created inside of + /// `op`, but this can be overwritten if necessary. fn evaluation_probe( &mut self, - op: impl FnOnce(&mut Self) -> Result<EvaluationResult, OverflowError>, + op: impl FnOnce(&mut Self, &mut ty::UniverseIndex) -> Result<EvaluationResult, OverflowError>, ) -> Result<EvaluationResult, OverflowError> { self.infcx.probe(|snapshot| -> Result<EvaluationResult, OverflowError> { - let outer_universe = self.infcx.universe(); - let result = op(self)?; + let mut outer_universe = self.infcx.universe(); + let result = op(self, &mut outer_universe)?; match self.infcx.leak_check(outer_universe, Some(snapshot)) { Ok(()) => {} @@ -586,9 +608,10 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> { }) } - /// Evaluates the predicates in `predicates` recursively. Note that - /// this applies projections in the predicates, and therefore + /// Evaluates the predicates in `predicates` recursively. This may + /// guide inference. If this is not desired, run it inside of a /// is run within an inference probe. + /// `probe`. #[instrument(skip(self, stack), level = "debug")] fn evaluate_predicates_recursively<'o, I>( &mut self, @@ -1194,7 +1217,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> { } match self.candidate_from_obligation(stack) { - Ok(Some(c)) => self.evaluate_candidate(stack, &c), + Ok(Some(c)) => self.evaluate_candidate(stack, &c, LeakCheckHigherRankedGoal::Yes), Ok(None) => Ok(EvaluatedToAmbig), Err(Overflow(OverflowError::Canonical)) => Err(OverflowError::Canonical), Err(..) => Ok(EvaluatedToErr), @@ -1219,6 +1242,10 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> { /// Further evaluates `candidate` to decide whether all type parameters match and whether nested /// obligations are met. Returns whether `candidate` remains viable after this further /// scrutiny. + /// + /// Depending on the value of [LeakCheckHigherRankedGoal], we may ignore the binder of the goal + /// when eagerly detecting higher ranked region errors via the `leak_check`. See that enum for + /// more info. #[instrument( level = "debug", skip(self, stack), @@ -1229,10 +1256,25 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> { &mut self, stack: &TraitObligationStack<'o, 'tcx>, candidate: &SelectionCandidate<'tcx>, + leak_check_higher_ranked_goal: LeakCheckHigherRankedGoal, ) -> Result<EvaluationResult, OverflowError> { - let mut result = self.evaluation_probe(|this| { - let candidate = (*candidate).clone(); - match this.confirm_candidate(stack.obligation, candidate) { + let mut result = self.evaluation_probe(|this, outer_universe| { + // We eagerly instantiate higher ranked goals to prevent universe errors + // from impacting candidate selection. This matches the behavior of the new + // solver. This slightly weakens type inference. + // + // In case there are no unresolved type or const variables this + // should still not be necessary to select a unique impl as any overlap + // relying on a universe error from higher ranked goals should have resulted + // in an overlap error in coherence. + let p = self.infcx.enter_forall_and_leak_universe(stack.obligation.predicate); + let obligation = stack.obligation.with(this.tcx(), ty::Binder::dummy(p)); + match leak_check_higher_ranked_goal { + LeakCheckHigherRankedGoal::No => *outer_universe = self.infcx.universe(), + LeakCheckHigherRankedGoal::Yes => {} + } + + match this.confirm_candidate(&obligation, candidate.clone()) { Ok(selection) => { debug!(?selection); this.evaluate_predicates_recursively( @@ -1657,8 +1699,14 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> { stack: &TraitObligationStack<'o, 'tcx>, where_clause_trait_ref: ty::PolyTraitRef<'tcx>, ) -> Result<EvaluationResult, OverflowError> { - self.evaluation_probe(|this| { - match this.match_where_clause_trait_ref(stack.obligation, where_clause_trait_ref) { + self.evaluation_probe(|this, outer_universe| { + // Eagerly instantiate higher ranked goals. + // + // See the comment in `evaluate_candidate` to see why. + let p = self.infcx.enter_forall_and_leak_universe(stack.obligation.predicate); + let obligation = stack.obligation.with(this.tcx(), ty::Binder::dummy(p)); + *outer_universe = self.infcx.universe(); + match this.match_where_clause_trait_ref(&obligation, where_clause_trait_ref) { Ok(obligations) => this.evaluate_predicates_recursively(stack.list(), obligations), Err(()) => Ok(EvaluatedToErr), } |