allow inference vars in type_implements_trait

1 files changed, 14 insertions, 1 deletions

diff --git a/compiler/rustc_middle/src/query/mod.rs b/compiler/rustc_middle/src/query/mod.rs
index 23ee0e05062..0986a465729 100644
--- a/compiler/rustc_middle/src/query/mod.rs
+++ b/compiler/rustc_middle/src/query/mod.rs
@@ -1559,9 +1559,22 @@ rustc_queries! {
         desc { "evaluating trait selection obligation `{}`", goal.value }
     }
 
+    /// Evaluates whether the given type implements the given trait
+    /// in the given environment.
+    ///
+    /// The inputs are:
+    ///
+    /// - the def-id of the trait
+    /// - the self type
+    /// - the *other* type parameters of the trait, excluding the self-type
+    /// - the parameter environment
+    ///
+    /// FIXME. If the type, trait, or environment has inference variables,
+    /// this yields `EvaluatedToUnknown`. It should be refactored
+    /// to use canonicalization, really.
     query type_implements_trait(
         key: (DefId, Ty<'tcx>, SubstsRef<'tcx>, ty::ParamEnv<'tcx>, )
-    ) -> bool {
+    ) -> traits::EvaluationResult {
         desc { "evaluating `type_implements_trait` `{:?}`", key }
     }