chore: be able to hide webServer stderr (#23063)

Follow-up to https://github.com/microsoft/playwright/pull/22564.

docs/src/test-api/class-testconfig.md

@@ -571,6 +571,7 @@ export default defineConfig({
   - `timeout` ?<[int]> How long to wait for the process to start up and be available in milliseconds. Defaults to 60000.
   - `reuseExistingServer` ?<[boolean]> If true, it will re-use an existing server on the `port` or `url` when available. If no server is running on that `port` or `url`, it will run the command to start a new server. If `false`, it will throw if an existing process is listening on the `port` or `url`. This should be commonly set to `!process.env.CI` to allow the local dev server when running tests locally.
   - `stdout` ?<["pipe"|"ignore"]> If `"pipe"`, it will pipe the stdout of the command to the process stdout. If `"ignore"`, it will ignore the stdout of the command. Default to `"ignore"`.
+  - `stderr` ?<["pipe"|"ignore"]> Whether to pipe the stderr of the command to the process stderr or ignore it. Defaults to `"pipe"`.
   - `cwd` ?<[string]> Current working directory of the spawned process, defaults to the directory of the configuration file.
   - `env` ?<[Object]<[string], [string]>> Environment variables to set for the command, `process.env` by default.
 

docs/src/test-webserver-js.md

@@ -29,6 +29,7 @@ export default defineConfig({
 | `url`| URL of your http server that is expected to return a 2xx, 3xx, 400, 401, 402, or 403 status code when the server is ready to accept connections. |
 | `reuseExistingServer`| If `true`, it will re-use an existing server on the url when available. If no server is running on that url, it will run the command to start a new server. If `false`, it will throw if an existing process is listening on the url. To see the stdout, you can set the `DEBUG=pw:webserver` environment variable. |
 | `stdout` | If `"pipe"`, it will pipe the stdout of the command to the process stdout. If `"ignore"`, it will ignore the stdout of the command. Default to `"ignore"`. |
+| `stderr` | Whether to pipe the stderr of the command to the process stderr or ignore it. Defaults to `"pipe"`. |
 
 ## Adding a server timeout
 

packages/playwright-test/src/plugins/webServerPlugin.ts

@@ -35,6 +35,7 @@ export type WebServerPluginOptions = {
   cwd?: string;
   env?: { [key: string]: string; };
   stdout?: 'pipe' | 'ignore';
+  stderr?: 'pipe' | 'ignore';
 };
 
 const DEFAULT_ENVIRONMENT_VARIABLES = {
@@ -107,7 +108,10 @@ export class WebServerPlugin implements TestRunnerPlugin {
 
     debugWebServer(`Process started`);
 
-    launchedProcess.stderr!.on('data', line => this._reporter!.onStdErr?.('[WebServer] ' + line.toString()));
+    launchedProcess.stderr!.on('data', line => {
+      if (debugWebServer.enabled || (this._options.stderr === 'pipe' || !this._options.stderr))
+        this._reporter!.onStdErr?.('[WebServer] ' + line.toString());
+    });
     launchedProcess.stdout!.on('data', line => {
       if (debugWebServer.enabled || this._options.stdout === 'pipe')
         this._reporter!.onStdOut?.('[WebServer] ' + line.toString());

packages/playwright-test/types/test.d.ts

@@ -6504,6 +6504,11 @@ interface TestConfigWebServer {
    */
   stdout?: "pipe"|"ignore";
 
+  /**
+   * Whether to pipe the stderr of the command to the process stderr or ignore it. Defaults to `"pipe"`.
+   */
+  stderr?: "pipe"|"ignore";
+
   /**
    * Current working directory of the spawned process, defaults to the directory of the configuration file.
    */

tests/playwright-test/web-server.spec.ts

@@ -679,5 +679,27 @@ test('should forward stdout when set to "pipe"', async ({ runInlineTest }, { wor
   expect(result.exitCode).toBe(0);
   expect(result.passed).toBe(1);
   expect(result.output).toContain('[WebServer] listening');
-  expect(result.output).toContain('[WebServer] error from server'); // stderr is always getting forwarded
+  expect(result.output).toContain('[WebServer] error from server'); // stderr is piped by default
+});
+
+test('should be able to ignore "stderr"', async ({ runInlineTest }, { workerIndex }) => {
+  const port = workerIndex * 2 + 10500;
+  const result = await runInlineTest({
+    'test.spec.ts': `
+      import { test, expect } from '@playwright/test';
+      test('pass', async ({}) => {});
+    `,
+    'playwright.config.ts': `
+      module.exports = {
+        webServer: {
+          command: 'node ${JSON.stringify(SIMPLE_SERVER_PATH)} ${port}',
+          port: ${port},
+          stderr: 'ignore',
+        }
+      };
+    `,
+  }, undefined);
+  expect(result.exitCode).toBe(0);
+  expect(result.passed).toBe(1);
+  expect(result.output).not.toContain('error from server');
 });