fix(@angular/build): fail build and exclude routes when prerendering fails

When a prerendered route failed to render (such as when a component throws
during route activation), the render worker returned null content which was
silently skipped. Consequently, no HTML file was written, but the build still
reported the route in prerender statistics, included it in prerendered-routes.json,
and exited with code 0.

Now:
- The render worker throws an error if content is null ('The content returned was empty.').
- Prerendering records the error so the build fails with a non-zero exit code.
- Prerendered routes recorded for manifest and statistics are derived strictly from routes that produced output files.

Closes #33965

Author: alan-agius4

packages/angular/build/src/builders/application/execute-post-bundle.ts

@@ -157,7 +157,13 @@ export async function executePostBundleSteps(
       'The "index" option is required when using the "ssg" or "appShell" options.',
     );
 
-    const { output, warnings, errors, serializableRouteTreeNode } = await prerenderPages(
+    const {
+      output,
+      warnings,
+      errors,
+      serializableRouteTreeNode,
+      prerenderedRoutes: generatedPrerenderedRoutes,
+    } = await prerenderPages(
       workspaceRoot,
       baseHref,
       appShellOptions,
@@ -171,6 +177,7 @@ export async function executePostBundleSteps(
 
     allErrors.push(...errors);
     allWarnings.push(...warnings);
+    Object.assign(prerenderedRoutes, generatedPrerenderedRoutes);
 
     const indexHasBeenPrerendered = output[indexHtmlOptions.output];
     for (const [path, { content, appShellRoute }] of Object.entries(output)) {
@@ -195,10 +202,6 @@ export async function executePostBundleSteps(
     const serializableRouteTreeNodeForManifest: WritableSerializableRouteTreeNode = [];
     for (const metadata of serializableRouteTreeNode) {
       serializableRouteTreeNodeForManifest.push(metadata);
-
-      if (metadata.renderMode === RouteRenderMode.Prerender && !metadata.route.includes('*')) {
-        prerenderedRoutes[metadata.route] = { headers: metadata.headers };
-      }
     }
 
     if (outputMode === OutputMode.Server) {

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

@@ -10,7 +10,10 @@ import { readFile } from 'node:fs/promises';
 import { extname, posix } from 'node:path';
 import { NormalizedApplicationBuildOptions } from '../../builders/application/options';
 import { OutputMode } from '../../builders/application/schema';
-import { BuildOutputAsset } from '../../tools/esbuild/bundler-execution-result';
+import {
+  BuildOutputAsset,
+  PrerenderedRoutesRecord,
+} from '../../tools/esbuild/bundler-execution-result';
 import { BuildOutputFile, BuildOutputFileType } from '../../tools/esbuild/bundler-files';
 import { assertIsError } from '../error';
 import { toPosixPath } from '../path';
@@ -65,6 +68,7 @@ export async function prerenderPages(
   output: PrerenderOutput;
   warnings: string[];
   errors: string[];
+  prerenderedRoutes: PrerenderedRoutesRecord;
   serializableRouteTreeNode: SerializableRouteTreeNode;
 }> {
   const rawOutputFiles: Record<string, string> = {};
@@ -167,6 +171,7 @@ export async function prerenderPages(
       errors,
       warnings,
       output: {},
+      prerenderedRoutes: {},
       serializableRouteTreeNode,
     };
   }
@@ -200,10 +205,28 @@ export async function prerenderPages(
 
   errors.push(...renderingErrors);
 
+  const prerenderedRoutes: PrerenderedRoutesRecord = {};
+  const baseHrefPathnameWithLeadingSlash = new URL(baseHref, 'http://localhost').pathname;
+
+  for (const metadata of serializableRouteTreeNodeForPrerender) {
+    const routeWithoutBaseHref = addTrailingSlash(metadata.route).startsWith(
+      baseHrefPathnameWithLeadingSlash,
+    )
+      ? addLeadingSlash(metadata.route.slice(baseHrefPathnameWithLeadingSlash.length))
+      : metadata.route;
+
+    const outPath = stripLeadingSlash(posix.join(routeWithoutBaseHref, 'index.html'));
+
+    if (output[outPath]) {
+      prerenderedRoutes[metadata.route] = { headers: metadata.headers };
+    }
+  }
+
   return {
     errors,
     warnings,
     output,
+    prerenderedRoutes,
     serializableRouteTreeNode,
   };
 }
@@ -305,20 +328,20 @@ async function renderPages(
       const renderBatchPromise: Promise<RenderResult> = renderWorker.run(urls);
       const batchResultPromise = renderBatchPromise
         .then((results) => {
-          for (const { url, content, error } of results) {
-            if (error) {
-              errors.push(`An error occurred while prerendering route '${url}'.\n\n${error}`);
+          for (const result of results) {
+            if ('error' in result) {
+              errors.push(
+                `An error occurred while prerendering route '${result.url}'.\n\n${result.error}`,
+              );
               continue;
             }
 
-            if (content !== null) {
-              const routeInfo = routeOutPathMap.get(url);
-              if (routeInfo) {
-                output[routeInfo.outPath] = {
-                  content,
-                  appShellRoute: routeInfo.isAppShell,
-                };
-              }
+            const routeInfo = routeOutPathMap.get(result.url);
+            if (routeInfo) {
+              output[routeInfo.outPath] = {
+                content: result.content,
+                appShellRoute: routeInfo.isAppShell,
+              };
             }
           }
         })

packages/angular/build/src/utils/server-rendering/render-worker.ts

@@ -21,11 +21,15 @@ export interface RenderWorkerData extends ESMInMemoryFileLoaderWorkerData {
   hasSsrEntry: boolean;
 }
 
-export interface RenderResultItem {
-  url: string;
-  content: string | null;
-  error?: string;
-}
+export type RenderResultItem =
+  | {
+      url: string;
+      content: string;
+    }
+  | {
+      url: string;
+      error: string;
+    };
 
 export type RenderResult = RenderResultItem[];
 
@@ -74,12 +78,16 @@ async function renderPages(urls: string[]): Promise<RenderResult> {
   for (const currentUrl of urls) {
     try {
       const content = await renderPage(currentUrl, angularServerApp);
+
+      if (content === null) {
+        throw new Error('The content returned was empty.');
+      }
+
       results.push({ url: currentUrl, content });
     } catch (err) {
       assertIsError(err);
       results.push({
         url: currentUrl,
-        content: null,
         error: err.stack ?? err.message ?? err.code ?? `${err}`,
       });
     }

tests/e2e/tests/build/prerender/error-component-render.ts

@@ -0,0 +1,73 @@
+import { ng } from '../../../utils/process';
+import { getGlobalVariable } from '../../../utils/env';
+import { expectFileNotToExist, readFile, rimraf, writeMultipleFiles } from '../../../utils/fs';
+import { match } from 'node:assert';
+import { expectToFail } from '../../../utils/utils';
+import { useSha } from '../../../utils/project';
+import { installWorkspacePackages } from '../../../utils/packages';
+import assert from 'node:assert';
+
+export default async function () {
+  const useWebpackBuilder = !getGlobalVariable('argv')['esbuild'];
+  if (useWebpackBuilder) {
+    return;
+  }
+
+  // Forcibly remove in case another test doesn't clean itself up.
+  await rimraf('node_modules/@angular/ssr');
+  await ng('add', '@angular/ssr', '--skip-confirmation');
+  await useSha();
+  await installWorkspacePackages();
+
+  await writeMultipleFiles({
+    'src/app/app.routes.ts': `
+      import { Routes } from '@angular/router';
+      import { Component } from '@angular/core';
+
+      @Component({
+        selector: 'app-home',
+        standalone: true,
+        template: '<p>home works!</p>',
+      })
+      export class HomeRoute {}
+
+      @Component({
+        selector: 'app-second',
+        standalone: true,
+        template: '<p>second works!</p>',
+      })
+      export class SecondRoute {
+        constructor() {
+          throw new Error('render failure');
+        }
+      }
+
+      export const routes: Routes = [
+        { path: '', component: HomeRoute },
+        { path: 'second', component: SecondRoute },
+      ];
+    `,
+    'src/app/app.routes.server.ts': `
+      import { RenderMode, ServerRoute } from '@angular/ssr';
+
+      export const serverRoutes: ServerRoute[] = [
+        { path: 'second', renderMode: RenderMode.Prerender },
+        { path: '**', renderMode: RenderMode.Prerender },
+      ];
+    `,
+  });
+
+  const { message } = await expectToFail(() => ng('build', '--output-mode=server'));
+
+  match(message, /An error occurred while prerendering route '\/second'\./);
+
+  await expectFileNotToExist('dist/test-project/browser/second/index.html');
+
+  // prerendered-routes.json should only contain successfully prerendered routes
+  try {
+    const stats = JSON.parse(await readFile('dist/test-project/prerendered-routes.json'));
+    assert.strictEqual(stats.routes['/second'], undefined);
+  } catch {
+    // If prerendered-routes.json was not emitted on failure, that is also valid.
+  }
+}