fix(@angular/build): handle APP_BASE_HREF correctly in prerendered routes

This commit resolves path stripping issues when `APP_BASE_HREF` does not align with the expected value.

Closes #28775

(cherry picked from commit a1fa483)

Author: alan-agius4

packages/angular/build/src/utils/server-rendering/prerender.ts

@@ -219,10 +219,11 @@ async function renderPages(
     const baseHrefWithLeadingSlash = addLeadingSlash(baseHref);
 
     for (const { route, redirectTo, renderMode } of serializableRouteTreeNode) {
-      // Remove base href from file output path.
-      const routeWithoutBaseHref = addLeadingSlash(
-        route.slice(baseHrefWithLeadingSlash.length - 1),
-      );
+      // Remove the base href from the file output path.
+      const routeWithoutBaseHref = addTrailingSlash(route).startsWith(baseHrefWithLeadingSlash)
+        ? addLeadingSlash(route.slice(baseHrefWithLeadingSlash.length - 1))
+        : route;
+
       const outPath = posix.join(removeLeadingSlash(routeWithoutBaseHref), 'index.html');
 
       if (typeof redirectTo === 'string') {
@@ -336,11 +337,15 @@ async function getAllRoutes(
 }
 
 function addLeadingSlash(value: string): string {
-  return value.charAt(0) === '/' ? value : '/' + value;
+  return value[0] === '/' ? value : '/' + value;
+}
+
+function addTrailingSlash(url: string): string {
+  return url[url.length - 1] === '/' ? url : `${url}/`;
 }
 
 function removeLeadingSlash(value: string): string {
-  return value.charAt(0) === '/' ? value.slice(1) : value;
+  return value[0] === '/' ? value.slice(1) : value;
 }
 
 /**

tests/legacy-cli/e2e/tests/build/server-rendering/server-routes-output-mode-static-i18n_APP_BASE_HREF.ts

@@ -0,0 +1,106 @@
+import { join } from 'node:path';
+import { existsSync } from 'node:fs';
+import assert from 'node:assert';
+import { expectFileNotToExist, expectFileToMatch, writeFile } from '../../../utils/fs';
+import { ng, noSilentNg, silentNg } from '../../../utils/process';
+import { installWorkspacePackages, uninstallPackage } from '../../../utils/packages';
+import { useSha } from '../../../utils/project';
+import { getGlobalVariable } from '../../../utils/env';
+import { langTranslations, setupI18nConfig } from '../../i18n/setup';
+
+export default async function () {
+  assert(
+    getGlobalVariable('argv')['esbuild'],
+    'This test should not be called in the Webpack suite.',
+  );
+
+  // Setup project
+  await setupI18nConfig();
+
+  // Forcibly remove in case another test doesn't clean itself up.
+  await uninstallPackage('@angular/ssr');
+  await ng('add', '@angular/ssr', '--server-routing', '--skip-confirmation', '--skip-install');
+  await useSha();
+  await installWorkspacePackages();
+
+  // Add routes
+  await writeFile(
+    'src/app/app.routes.ts',
+    `
+  import { Routes } from '@angular/router';
+  import { HomeComponent } from './home/home.component';
+  import { SsgComponent } from './ssg/ssg.component';
+
+  export const routes: Routes = [
+    {
+      path: '',
+      component: HomeComponent,
+    },
+    {
+      path: 'ssg',
+      component: SsgComponent,
+    },
+    {
+      path: '**',
+      component: HomeComponent,
+    },
+  ];
+  `,
+  );
+
+  // Add server routing
+  await writeFile(
+    'src/app/app.routes.server.ts',
+    `
+  import { RenderMode, ServerRoute } from '@angular/ssr';
+
+  export const serverRoutes: ServerRoute[] = [
+    {
+      path: '**',
+      renderMode: RenderMode.Prerender,
+    },
+  ];
+  `,
+  );
+
+  await writeFile(
+    'src/app/app.config.ts',
+    `
+      import { ApplicationConfig, provideZoneChangeDetection } from '@angular/core';
+      import { provideRouter } from '@angular/router';
+
+      import { routes } from './app.routes';
+      import { provideClientHydration } from '@angular/platform-browser';
+      import { APP_BASE_HREF } from '@angular/common';
+
+      export const appConfig: ApplicationConfig = {
+        providers: [
+          provideZoneChangeDetection({ eventCoalescing: true }),
+          provideRouter(routes),
+          provideClientHydration(),
+          {
+            provide: APP_BASE_HREF,
+            useValue: '/',
+          },
+        ],
+      };
+      `,
+  );
+
+  // Generate components for the above routes
+  await silentNg('generate', 'component', 'home');
+  await silentNg('generate', 'component', 'ssg');
+
+  await noSilentNg('build', '--output-mode=static');
+
+  for (const { lang, outputPath } of langTranslations) {
+    await expectFileToMatch(join(outputPath, 'index.html'), `<p id="locale">${lang}</p>`);
+    await expectFileToMatch(join(outputPath, 'ssg/index.html'), `<p id="locale">${lang}</p>`);
+  }
+
+  // Check that server directory does not exist
+  assert(
+    !existsSync('dist/test-project/server'),
+    'Server directory should not exist when output-mode is static',
+  );
+}