From 6c61db44073ce96176850ea5db5dc99624823d91 Mon Sep 17 00:00:00 2001 From: Ilya Yanok Date: Thu, 28 Oct 2021 12:49:46 +0000 Subject: [PATCH] Use `is_global` in `candidate_should_be_dropped_in_favor_of` This manifistated in #90195 with compiler being unable to keep one candidate for a trait impl, if where is a global impl and more than one trait bound in the where clause. Before #87280 `candidate_should_be_dropped_in_favor_of` was using `TypeFoldable::is_global()` that was enough to discard the two `ParamCandidate`s. But #87280 changed it to use `TypeFoldable::is_known_global()` instead, which is pessimistic, so now the compiler drops the global impl instead (because `is_known_global` is not sure) and then can't decide between the two `ParamCandidate`s. Switching it to use `is_global` again solves the issue. Fixes #90195. --- compiler/rustc_trait_selection/src/traits/select/mod.rs | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/compiler/rustc_trait_selection/src/traits/select/mod.rs b/compiler/rustc_trait_selection/src/traits/select/mod.rs index 1b26e38fe0e4..8bd842a5e062 100644 --- a/compiler/rustc_trait_selection/src/traits/select/mod.rs +++ b/compiler/rustc_trait_selection/src/traits/select/mod.rs @@ -1548,7 +1548,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> { // the param_env so that it can be given the lowest priority. See // #50825 for the motivation for this. let is_global = - |cand: &ty::PolyTraitRef<'_>| cand.is_known_global() && !cand.has_late_bound_regions(); + |cand: &ty::PolyTraitRef<'tcx>| cand.is_global(self.infcx.tcx) && !cand.has_late_bound_regions(); // (*) Prefer `BuiltinCandidate { has_nested: false }`, `PointeeCandidate`, // and `DiscriminantKindCandidate` to anything else.