refactor(core): expose function to assert type of variables (angular#62648)

Adds the `ɵassertType` function that will be used during type checking to assert the type of a value.

PR Close angular#62648

Author: crisbeto

packages/compiler/src/render3/r3_identifiers.ts

@@ -469,4 +469,5 @@ export class Identifiers {
   static InputSignalBrandWriteType = {name: 'ɵINPUT_SIGNAL_BRAND_WRITE_TYPE', moduleName: CORE};
   static UnwrapDirectiveSignalInputs = {name: 'ɵUnwrapDirectiveSignalInputs', moduleName: CORE};
   static unwrapWritableSignal = {name: 'ɵunwrapWritableSignal', moduleName: CORE};
+  static assertType = {name: 'ɵassertType', moduleName: CORE};
 }

packages/core/src/core_private_export.ts

@@ -171,3 +171,4 @@ export {getClosestComponentName as ɵgetClosestComponentName} from './internal/g
 export {getComponentDef as ɵgetComponentDef} from './render3/def_getters';
 export {DEHYDRATED_BLOCK_REGISTRY as ɵDEHYDRATED_BLOCK_REGISTRY} from './defer/registry';
 export {TimerScheduler as ɵTimerScheduler} from './defer/timer_scheduler';
+export {ɵassertType} from './type_checking';

packages/core/src/type_checking.ts

@@ -0,0 +1,13 @@
+/*!
+ * @license
+ * Copyright Google LLC All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.dev/license
+ */
+
+/**
+ * Utility function used during template type checking to assert that a value is of a certain type.
+ * @codeGenApi
+ */
+export function ɵassertType<T>(value: unknown): asserts value is T {}

packages/core/test/render3/jit_environment_spec.ts

@@ -34,6 +34,7 @@ const AOT_ONLY = new Set<string>([
   'ɵINPUT_SIGNAL_BRAND_WRITE_TYPE',
   'ɵUnwrapDirectiveSignalInputs',
   'ɵunwrapWritableSignal',
+  'ɵassertType',
 ]);
 
 /**