add AliasEq to PredicateKind

compiler/rustc_trait_selection/src/solve/fulfill.rs

@@ -73,6 +73,11 @@ impl<'tcx> TraitEngine<'tcx> for FulfillmentCtxt<'tcx> {
                                         MismatchedProjectionTypes { err: TypeError::Mismatch },
                                     )
                                 }
+                                ty::PredicateKind::AliasEq(_, _) => {
+                                    FulfillmentErrorCode::CodeProjectionError(
+                                        MismatchedProjectionTypes { err: TypeError::Mismatch },
+                                    )
+                                }
                                 ty::PredicateKind::Subtype(pred) => {
                                     let (a, b) = infcx.instantiate_binder_with_placeholders(
                                         goal.predicate.kind().rebind((pred.a, pred.b)),

compiler/rustc_trait_selection/src/solve/mod.rs

@@ -302,6 +302,10 @@ impl<'a, 'tcx> EvalCtxt<'a, 'tcx> {
                 ty::PredicateKind::TypeWellFormedFromEnv(..) => {
                     bug!("TypeWellFormedFromEnv is only used for Chalk")
                 }
+                ty::PredicateKind::AliasEq(..) => {
+                    // FIXME(deferred_projection_equality)
+                    todo!()
+                }
             }
         } else {
             let kind = self.infcx.instantiate_binder_with_placeholders(kind);