fix ice with trait obj dummy self

Author: mark-i-m

src/librustc_typeck/variance/constraints.rs

@@ -315,11 +315,9 @@ impl<'a, 'tcx> ConstraintContext<'a, 'tcx> {
  self.add_constraints_from_region(current, r, contra);
 
  if let Some(poly_trait_ref) = data.principal() {
- let poly_trait_ref = poly_trait_ref
- .with_self_ty(self.tcx(), self.tcx().types.trait_object_dummy_self);
- self.add_constraints_from_trait_ref(
+ self.add_constraints_from_invariant_substs(
  current,
- *poly_trait_ref.skip_binder(),
+ poly_trait_ref.skip_binder().substs,
  variance,
  );
  }