Properly compare previously shadowed values

The shadowing lead to an incorrect comparison. Rename it and compare it
properly. compiler-errors told me that I should just include the fix
here without a test.

Author: Noratrieb

compiler/rustc_hir_typeck/src/_match.rs

@@ -538,8 +538,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                                 // FIXME(rpitit): This will need to be fixed when we move to associated types
                                 assert!(matches!(
                                     *trait_pred.trait_ref.self_ty().kind(),
-                                    ty::Alias(_, ty::AliasTy { def_id, substs, .. })
-                                    if def_id == rpit_def_id && substs == substs
+                                    ty::Alias(_, ty::AliasTy { def_id, substs: alias_substs, .. })
+                                    if def_id == rpit_def_id && substs == alias_substs
                                 ));
                                 ty::PredicateKind::Clause(ty::Clause::Trait(
                                     trait_pred.with_self_ty(self.tcx, ty),
@@ -548,8 +548,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                             ty::PredicateKind::Clause(ty::Clause::Projection(mut proj_pred)) => {
                                 assert!(matches!(
                                     *proj_pred.projection_ty.self_ty().kind(),
-                                    ty::Alias(_, ty::AliasTy { def_id, substs, .. })
-                                    if def_id == rpit_def_id && substs == substs
+                                    ty::Alias(_, ty::AliasTy { def_id, substs: alias_substs, .. })
+                                    if def_id == rpit_def_id && substs == alias_substs
                                 ));
                                 proj_pred = proj_pred.with_self_ty(self.tcx, ty);
                                 ty::PredicateKind::Clause(ty::Clause::Projection(proj_pred))