make WF(?T: Foo) flounder

Author: nikomatsakis

chalk-solve/src/clauses.rs

@@ -301,6 +301,10 @@ fn program_clauses_that_could_match<I: Interner>(
                 .to_program_clauses(builder),
         },
         DomainGoal::WellFormed(WellFormed::Trait(trait_predicate)) => {
+            let self_ty = trait_predicate.self_type_parameter(interner);
+            if self_ty.bound(interner).is_some() || self_ty.inference_var(interner).is_some() {
+                return Err(Floundered);
+            }
             db.trait_datum(trait_predicate.trait_id)
                 .to_program_clauses(builder);
         }