docs(docs-infra): ensure all redirections are absolute

fixes #64824

(cherry picked from commit 434ddbcfc9)

adev/src/app/routing/redirections.spec.ts

@@ -0,0 +1,31 @@
+/*!
+ * @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
+ */
+
+import {REDIRECT_ROUTES} from './redirections';
+import {Route} from '@angular/router';
+
+describe('REDIRECT_ROUTES', () => {
+  it('should have all redirectTo values starting with a "/"', () => {
+    const checkRoutes = (routes: Route[]) => {
+      for (const route of routes) {
+        if (route.redirectTo) {
+          if (typeof route.redirectTo === 'string') {
+            expect(route.redirectTo.startsWith('/'))
+              .withContext(`Invalid redirectTo: ${route.redirectTo}`)
+              .toBe(true);
+          }
+        }
+        if (route.children) {
+          checkRoutes(route.children);
+        }
+      }
+    };
+
+    checkRoutes(REDIRECT_ROUTES);
+  });
+});

adev/src/app/routing/redirections.ts

@@ -10,20 +10,22 @@ import {Route} from '@angular/router';
 /**
  * This file contains the redirections we keep to prevent breakages on existing links
  * that may exist on the internet and over which we have no control.
+ *
+ * The redirectTo should always that start with a "/" to avoid relative redirections.
  */
 
 export const REDIRECT_ROUTES: Route[] = [
   {
     path: 'guide/di/dependency-injection',
-    redirectTo: 'guide/di',
+    redirectTo: '/guide/di',
   },
   {
     path: 'guide/di/creating-injectable-service',
-    redirectTo: 'guide/di/creating-and-using-services',
+    redirectTo: '/guide/di/creating-and-using-services',
   },
   {
     path: 'guide/di/dependency-injection-providers',
-    redirectTo: 'guide/di/defining-dependency-providers',
+    redirectTo: '/guide/di/defining-dependency-providers',
   },
   {
     path: 'guide/defer',