diff options
Diffstat (limited to 'compiler')
| -rw-r--r-- | compiler/rustc_infer/src/infer/at.rs | 11 | ||||
| -rw-r--r-- | compiler/rustc_trait_selection/src/traits/coherence.rs | 8 |
2 files changed, 16 insertions, 3 deletions
diff --git a/compiler/rustc_infer/src/infer/at.rs b/compiler/rustc_infer/src/infer/at.rs index 2797d079761..c32c3aa6d29 100644 --- a/compiler/rustc_infer/src/infer/at.rs +++ b/compiler/rustc_infer/src/infer/at.rs @@ -65,8 +65,15 @@ impl<'tcx> InferCtxt<'tcx> { /// Forks the inference context, creating a new inference context with the same inference /// variables in the same state. This can be used to "branch off" many tests from the same - /// common state. Used in coherence. + /// common state. pub fn fork(&self) -> Self { + self.fork_with_intercrate(self.intercrate) + } + + /// Forks the inference context, creating a new inference context with the same inference + /// variables in the same state, except possibly changing the intercrate mode. This can be + /// used to "branch off" many tests from the same common state. Used in negative coherence. + pub fn fork_with_intercrate(&self, intercrate: bool) -> Self { Self { tcx: self.tcx, defining_use_anchor: self.defining_use_anchor, @@ -81,7 +88,7 @@ impl<'tcx> InferCtxt<'tcx> { tainted_by_errors: self.tainted_by_errors.clone(), err_count_on_creation: self.err_count_on_creation, universe: self.universe.clone(), - intercrate: self.intercrate, + intercrate, next_trait_solver: self.next_trait_solver, } } diff --git a/compiler/rustc_trait_selection/src/traits/coherence.rs b/compiler/rustc_trait_selection/src/traits/coherence.rs index b232f34fb19..c4c0428dcc1 100644 --- a/compiler/rustc_trait_selection/src/traits/coherence.rs +++ b/compiler/rustc_trait_selection/src/traits/coherence.rs @@ -397,6 +397,8 @@ fn impl_intersection_has_negative_obligation( ) -> bool { debug!("negative_impl(impl1_def_id={:?}, impl2_def_id={:?})", impl1_def_id, impl2_def_id); + // N.B. We need to unify impl headers *with* intercrate mode, even if proving negative predicates + // do not need intercrate mode enabled. let ref infcx = tcx.infer_ctxt().intercrate(true).with_next_trait_solver(true).build(); let root_universe = infcx.universe(); assert_eq!(root_universe, ty::UniverseIndex::ROOT); @@ -554,7 +556,11 @@ fn try_prove_negated_where_clause<'tcx>( return false; }; - let ref infcx = root_infcx.fork(); + // N.B. We don't need to use intercrate mode here because we're trying to prove + // the *existence* of a negative goal, not the non-existence of a positive goal. + // Without this, we over-eagerly register coherence ambiguity candidates when + // impl candidates do exist. + let ref infcx = root_infcx.fork_with_intercrate(false); let ocx = ObligationCtxt::new(infcx); ocx.register_obligation(Obligation::new( |