fix(@angular/ssr): introduce DI token to signal route discovery process

goldens/public-api/angular/ssr/index.api.md

@@ -6,6 +6,7 @@
 
 import { DefaultExport } from '@angular/router';
 import { EnvironmentProviders } from '@angular/core';
+import { InjectionToken } from '@angular/core';
 import { Provider } from '@angular/core';
 import { Type } from '@angular/core';
 
@@ -26,6 +27,9 @@ export interface AngularAppEngineOptions {
 // @public
 export function createRequestHandler(handler: RequestHandlerFunction): RequestHandlerFunction;
 
+// @public
+export const IS_DISCOVERING_ROUTES: InjectionToken<boolean>;
+
 // @public
 export enum PrerenderFallback {
     Client = 1,

packages/angular/ssr/public_api.ts

@@ -24,3 +24,5 @@ export {
   type ServerRouteServer,
   type ServerRouteCommon,
 } from './src/routes/route-config';
+
+export { IS_DISCOVERING_ROUTES } from './src/routes/ng-routes';

packages/angular/ssr/src/routes/ng-routes.ts

@@ -11,6 +11,7 @@ import {
   ApplicationRef,
   Compiler,
   EnvironmentInjector,
+  InjectionToken,
   Injector,
   createEnvironmentInjector,
   runInInjectionContext,
@@ -23,6 +24,7 @@ import {
   Router,
   ɵloadChildren as loadChildrenHelper,
 } from '@angular/router';
+
 import { ServerAssets } from '../assets';
 import { Console } from '../console';
 import { AngularAppManifest, getAngularAppManifest } from '../manifest';
@@ -39,6 +41,22 @@ import {
 } from './route-config';
 import { RouteTree, RouteTreeNodeMetadata } from './route-tree';
 
+/**
+ * A DI token that indicates whether the application is in the process of discovering routes.
+ *
+ * This token is provided with the value `true` when route discovery is active, allowing other
+ * parts of the application to conditionally execute logic. For example, it can be used to
+ * disable features or behaviors that are not necessary or might interfere with the route
+ * discovery process.
+ */
+export const IS_DISCOVERING_ROUTES = new InjectionToken<boolean>(
+  typeof ngDevMode === 'undefined' || ngDevMode ? 'IS_DISCOVERING_ROUTES' : '',
+  {
+    providedIn: 'platform',
+    factory: () => false,
+  },
+);
+
 interface Route extends AngularRoute {
   ɵentryName?: string;
 }
@@ -623,6 +641,10 @@ export async function getRoutesFromAngularRouterConfig(
       provide: ɵENABLE_ROOT_COMPONENT_BOOTSTRAP,
       useValue: false,
     },
+    {
+      provide: IS_DISCOVERING_ROUTES,
+      useValue: true,
+    },
   ]);
 
   try {

packages/angular/ssr/test/routes/ng-routes_spec.ts

@@ -18,7 +18,7 @@ import {
   provideRouter,
   withEnabledBlockingInitialNavigation,
 } from '@angular/router';
-import { extractRoutesAndCreateRouteTree } from '../../src/routes/ng-routes';
+import { IS_DISCOVERING_ROUTES, extractRoutesAndCreateRouteTree } from '../../src/routes/ng-routes';
 import { PrerenderFallback, RenderMode } from '../../src/routes/route-config';
 import { setAngularAppTestingManifest } from '../testing-utils';
 
@@ -790,4 +790,26 @@ describe('extractRoutesAndCreateRouteTree', () => {
       { route: '/home', renderMode: RenderMode.Server },
     ]);
   });
+
+  it('should provide `IS_DISCOVERING_ROUTES` as `true` during route discovery', async () => {
+    let isDiscoveringRoutes: boolean | undefined;
+
+    setAngularAppTestingManifest(
+      [
+        {
+          path: 'lazy',
+          loadChildren: () => {
+            isDiscoveringRoutes = inject(IS_DISCOVERING_ROUTES);
+
+            return [];
+          },
+        },
+      ],
+      [{ path: '**', renderMode: RenderMode.Server }],
+    );
+
+    await extractRoutesAndCreateRouteTree({ url });
+
+    expect(isDiscoveringRoutes).toBeTrue();
+  });
 });