add AliasTermTy::with_args to simplify a common-ish pattern

Author: WaffleLapkin

compiler/rustc_next_trait_solver/src/solve/eval_ctxt/mod.rs

@@ -965,7 +965,7 @@ where
             // Alternatively we could modify `Equate` for this case by adding another
             // variant to `StructurallyRelateAliases`.
             let identity_args = self.fresh_args_for_item(alias.def_id());
-            let rigid_ctor = ty::AliasTerm::new_from_args(cx, alias.kind, identity_args);
+            let rigid_ctor = alias.with_args(cx, identity_args);
             let ctor_term = rigid_ctor.to_term(cx);
             let obligations = self.delegate.eq_structurally_relating_aliases(
                 param_env,

compiler/rustc_trait_selection/src/traits/project.rs

@@ -1340,11 +1340,7 @@ fn confirm_coroutine_candidate<'cx, 'tcx>(
     };
 
     let predicate = ty::ProjectionPredicate {
-        projection_term: ty::AliasTerm::new_from_args(
-            tcx,
-            obligation.predicate.kind,
-            trait_ref.args,
-        ),
+        projection_term: obligation.predicate.with_args(tcx, trait_ref.args),
         term: ty.into(),
     };
 
@@ -1388,11 +1384,7 @@ fn confirm_future_candidate<'cx, 'tcx>(
     debug_assert_eq!(tcx.associated_item(obligation.predicate.def_id()).name(), sym::Output);
 
     let predicate = ty::ProjectionPredicate {
-        projection_term: ty::AliasTerm::new_from_args(
-            tcx,
-            obligation.predicate.kind,
-            trait_ref.args,
-        ),
+        projection_term: obligation.predicate.with_args(tcx, trait_ref.args),
         term: return_ty.into(),
     };
 
@@ -1434,11 +1426,7 @@ fn confirm_iterator_candidate<'cx, 'tcx>(
     debug_assert_eq!(tcx.associated_item(obligation.predicate.def_id()).name(), sym::Item);
 
     let predicate = ty::ProjectionPredicate {
-        projection_term: ty::AliasTerm::new_from_args(
-            tcx,
-            obligation.predicate.kind,
-            trait_ref.args,
-        ),
+        projection_term: obligation.predicate.with_args(tcx, trait_ref.args),
         term: yield_ty.into(),
     };
 
@@ -1488,11 +1476,7 @@ fn confirm_async_iterator_candidate<'cx, 'tcx>(
     let item_ty = args.type_at(0);
 
     let predicate = ty::ProjectionPredicate {
-        projection_term: ty::AliasTerm::new_from_args(
-            tcx,
-            obligation.predicate.kind,
-            trait_ref.args,
-        ),
+        projection_term: obligation.predicate.with_args(tcx, trait_ref.args),
         term: item_ty.into(),
     };
 
@@ -1898,11 +1882,7 @@ fn confirm_async_fn_kind_helper_candidate<'cx, 'tcx>(
     };
 
     let predicate = ty::ProjectionPredicate {
-        projection_term: ty::AliasTerm::new_from_args(
-            selcx.tcx(),
-            obligation.predicate.kind,
-            obligation.predicate.args,
-        ),
+        projection_term: obligation.predicate.with_args(selcx.tcx(), obligation.predicate.args),
         term: ty::CoroutineClosureSignature::tupled_upvars_by_closure_kind(
             selcx.tcx(),
             goal_kind_ty.expect_ty().to_opt_closure_kind().unwrap(),

compiler/rustc_type_ir/src/predicate.rs

@@ -769,6 +769,10 @@ impl<I: Interner> AliasTerm<I> {
         Ty::new_alias(interner, ty::AliasTy::new_from_args(interner, alias_ty_kind, self.args))
             .into()
     }
+
+    pub fn with_args(self, interner: I, args: I::GenericArgs) -> Self {
+        Self::new_from_args(interner, self.kind, args)
+    }
 }
 
 /// The following methods work only with (trait) associated term projections.

compiler/rustc_type_ir/src/relate.rs

@@ -256,7 +256,7 @@ impl<I: Interner> Relate<I> for ty::AliasTerm<I> {
                     relate_args_invariantly(relation, a.args, b.args)?
                 }
             };
-            Ok(ty::AliasTerm::new_from_args(relation.cx(), a.kind, args))
+            Ok(a.with_args(relation.cx(), args))
         }
     }
 }