only instantiate opaques with rigid types

compiler/rustc_borrowck/src/type_check/mod.rs

@@ -188,11 +188,7 @@ pub(crate) fn type_check<'mir, 'tcx>(
  &mut borrowck_context,
  );
 
- // FIXME(-Ztrait-solver=next): A bit dubious that we're only registering
- // predefined opaques in the typeck root.
- if infcx.next_trait_solver() && !infcx.tcx.is_typeck_child(body.source.def_id()) {
- checker.register_predefined_opaques_in_new_solver();
- }
+ checker.check_user_type_annotations();
 
  let mut verifier = TypeVerifier::new(&mut checker, promoted);
  verifier.visit_body(&body);
@@ -1021,7 +1017,11 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
  borrowck_context,
  reported_errors: Default::default(),
  };
- checker.check_user_type_annotations();
+ // FIXME(-Ztrait-solver=next): A bit dubious that we're only registering
+ // predefined opaques in the typeck root.
+ if infcx.next_trait_solver() && !infcx.tcx.is_typeck_child(body.source.def_id()) {
+ checker.register_predefined_opaques_in_new_solver();
+ }
  checker
  }
 

compiler/rustc_trait_selection/src/solve/project_goals/opaques.rs

@@ -53,6 +53,20 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
  return self.flounder(&matches);
  }
  }
+
+ let expected = match self.try_normalize_ty(goal.param_env, expected) {
+ Some(ty) => if ty.is_ty_var() {
+ return self.evaluate_added_goals_and_make_canonical_response(
+ Certainty::AMBIGUOUS,
+ )
+ } else {
+ ty
+ },
+ None => return self.evaluate_added_goals_and_make_canonical_response(
+ Certainty::OVERFLOW,
+ ),
+ };
+
  // Otherwise, define a new opaque type
  self.insert_hidden_type(opaque_type_key, goal.param_env, expected)?;
  self.add_item_bounds_for_hidden_type(