fix(@angular/build): prevent fallback to serving main.js for unknown requests

Previously, when an unknown `main.js` file was requested, the system would
automatically fall back to serving the default `main.js`. This behavior
could cause unexpected issues, such as incorrect resource loading or
misleading errors.

This fix ensures that only valid `main.js` files are served, preventing
unintended fallbacks and improving request handling.

Closes #29524

(cherry picked from commit 9a46be8)

Author: alan-agius4

packages/angular/build/src/builders/dev-server/tests/behavior/build-assets_spec.ts

@@ -142,7 +142,7 @@ describeServeBuilder(executeDevServer, DEV_SERVER_BUILDER_INFO, (harness, setupT
       expect(await response?.headers.get('Location')).toBe('/login/');
     });
 
-    it('serves a JavaScript asset named as a bundle', async () => {
+    it('serves a JavaScript asset named as a bundle (main.js)', async () => {
       await harness.writeFile('public/test/main.js', javascriptFileContent);
 
       setupTarget(harness, {
@@ -162,5 +162,17 @@ describeServeBuilder(executeDevServer, DEV_SERVER_BUILDER_INFO, (harness, setupT
       expect(result?.success).toBeTrue();
       expect(await response?.text()).toContain(javascriptFileContent);
     });
+
+    it('should return 404 when a JavaScript asset named as a bundle (main.js) does not exist', async () => {
+      setupTarget(harness, {});
+
+      harness.useTarget('serve', {
+        ...BASE_OPTIONS,
+      });
+
+      const { result, response } = await executeOnceAndFetch(harness, 'unknown/main.js');
+      expect(result?.success).toBeTrue();
+      expect(response?.status).toBe(404);
+    });
   });
 });

packages/angular/build/src/builders/dev-server/vite-server.ts

@@ -808,7 +808,11 @@ export async function setupServer(
       },
       // This is needed when `externalDependencies` is used to prevent Vite load errors.
       // NOTE: If Vite adds direct support for externals, this can be removed.
-      preTransformRequests: externalMetadata.explicitBrowser.length === 0,
+      // NOTE: Vite breaks the resolution of browser modules in SSR
+      //       when accessing a url with two or more segments (e.g., 'foo/bar'),
+      //       as they are not re-based from the base href.
+      preTransformRequests:
+        externalMetadata.explicitBrowser.length === 0 && ssrMode === ServerSsrMode.NoSsr,
     },
     ssr: {
       // Note: `true` and `/.*/` have different sematics. When true, the `external` option is ignored.

packages/angular/build/src/tools/vite/plugins/angular-memory-plugin.ts

@@ -62,24 +62,12 @@ export async function createAngularMemoryPlugin(
         return source;
       }
 
-      if (importer) {
+      if (importer && source[0] === '.') {
         const normalizedImporter = normalizePath(importer);
-        if (source[0] === '.' && normalizedImporter.startsWith(virtualProjectRoot)) {
+        if (normalizedImporter.startsWith(virtualProjectRoot)) {
           // Remove query if present
           const [importerFile] = normalizedImporter.split('?', 1);
           source = '/' + join(dirname(relative(virtualProjectRoot, importerFile)), source);
-        } else if (
-          !ssr &&
-          source[0] === '/' &&
-          importer.endsWith('index.html') &&
-          normalizedImporter.startsWith(virtualProjectRoot)
-        ) {
-          // This is only needed when using SSR and `angularSsrMiddleware` (old style) to correctly resolve
-          // .js files when using lazy-loading.
-          // Remove query if present
-          const [importerFile] = normalizedImporter.split('?', 1);
-          source =
-            '/' + join(dirname(relative(virtualProjectRoot, importerFile)), basename(source));
         }
       }