eagerly compute `sub_relations` again

1 files changed, 9 insertions, 5 deletions

diff --git a/compiler/rustc_next_trait_solver/src/solve/mod.rs b/compiler/rustc_next_trait_solver/src/solve/mod.rs
index 85f9d852d95..a2db21796a2 100644
--- a/compiler/rustc_next_trait_solver/src/solve/mod.rs
+++ b/compiler/rustc_next_trait_solver/src/solve/mod.rs
@@ -119,11 +119,15 @@ where
 
     #[instrument(level = "trace", skip(self))]
     fn compute_subtype_goal(&mut self, goal: Goal<I, ty::SubtypePredicate<I>>) -> QueryResult<I> {
-        if goal.predicate.a.is_ty_var() && goal.predicate.b.is_ty_var() {
-            self.evaluate_added_goals_and_make_canonical_response(Certainty::AMBIGUOUS)
-        } else {
-            self.sub(goal.param_env, goal.predicate.a, goal.predicate.b)?;
-            self.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
+        match (goal.predicate.a.kind(), goal.predicate.b.kind()) {
+            (ty::Infer(ty::TyVar(a_vid)), ty::Infer(ty::TyVar(b_vid))) => {
+                self.sub_ty_vids_raw(a_vid, b_vid);
+                self.evaluate_added_goals_and_make_canonical_response(Certainty::AMBIGUOUS)
+            }
+            _ => {
+                self.sub(goal.param_env, goal.predicate.a, goal.predicate.b)?;
+                self.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
+            }
         }
     }