chore: have pretty error if CT config has no defineConfig (#21318)

Fixes https://github.com/microsoft/playwright/issues/21312

packages/playwright-test/index.js

@@ -15,8 +15,8 @@
  */
 
 const pwt = require('./lib/index');
+const { defineConfig } = require('./lib/common/configLoader');
 const playwright = require('playwright-core');
-const defineConfig = config => config;
 const combinedExports = {
   ...playwright,
   ...pwt,

packages/playwright-test/src/common/configLoader.ts

@@ -26,6 +26,12 @@ import { setCurrentConfig } from './globals';
 
 export const defaultTimeout = 30000;
 
+const kDefineConfigWasUsed = Symbol('defineConfigWasUsed');
+export const defineConfig = (config: any) => {
+  config[kDefineConfigWasUsed] = true;
+  return config;
+};
+
 export class ConfigLoader {
   private _fullConfig: FullConfigInternal;
 
@@ -125,6 +131,7 @@ export class ConfigLoader {
     this._fullConfig._internal.ignoreSnapshots = takeFirst(config.ignoreSnapshots, baseFullConfig._internal.ignoreSnapshots);
     this._fullConfig.updateSnapshots = takeFirst(config.updateSnapshots, baseFullConfig.updateSnapshots);
     this._fullConfig._internal.plugins = ((config as any)._plugins || []).map((p: any) => ({ factory: p }));
+    this._fullConfig._internal.defineConfigWasUsed = !!(config as any)[kDefineConfigWasUsed];
 
     const workers = takeFirst(config.workers, '50%');
     if (typeof workers === 'string') {
@@ -457,6 +464,7 @@ export const baseFullConfig: FullConfigInternal = {
     cliGrep: undefined,
     cliGrepInvert: undefined,
     listOnly: false,
+    defineConfigWasUsed: false,
   }
 };
 

packages/playwright-test/src/common/types.ts

@@ -45,6 +45,7 @@ type ConfigInternal = {
   cliProjectFilter?: string[];
   testIdMatcher?: Matcher;
   passWithNoTests?: boolean;
+  defineConfigWasUsed: boolean;
 };
 
 /**

packages/playwright-test/src/mount.ts

@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-import type { Fixtures, Locator, Page, BrowserContextOptions, PlaywrightTestArgs, PlaywrightTestOptions, PlaywrightWorkerArgs, PlaywrightWorkerOptions, BrowserContext, ContextReuseMode } from './common/types';
+import type { Fixtures, Locator, Page, BrowserContextOptions, PlaywrightTestArgs, PlaywrightTestOptions, PlaywrightWorkerArgs, PlaywrightWorkerOptions, BrowserContext, ContextReuseMode, FullConfigInternal } from './common/types';
 import type { Component, JsxComponent, MountOptions } from '../types/component';
 
 let boundCallbacksForMount: Function[] = [];
@@ -37,7 +37,9 @@ export const fixtures: Fixtures<
 
     _ctWorker: [{ context: undefined, hash: '' }, { scope: 'worker' }],
 
-    page: async ({ page }, use) => {
+    page: async ({ page }, use, info) => {
+      if (!(info.config as FullConfigInternal)._internal.defineConfigWasUsed)
+        throw new Error('Component testing requires the use of the defineConfig() in your playwright-ct.config.{ts,js}: https://aka.ms/playwright/ct-define-config');
       await (page as any)._wrapApiCall(async () => {
         await page.exposeFunction('__ct_dispatch', (ordinal: number, args: any[]) => {
           boundCallbacksForMount[ordinal](...args);