fix(esmLoader): unref MessagePort in the main thread (#30271)

This prevents the process from not exiting forever due to an open port.

packages/playwright/src/transform/portTransport.ts

@@ -33,17 +33,33 @@ export class PortTransport {
       if (ackId) {
         const callback = this._callbacks.get(ackId);
         this._callbacks.delete(ackId);
+        this._resetRef();
         callback?.(result);
         return;
       }
     });
+    // Make sure to unref **after** adding a 'message' event listener.
+    // https://nodejs.org/api/worker_threads.html#portref
+    this._resetRef();
   }
 
   async send(method: string, params: any) {
     return await new Promise<any>(f => {
       const id = ++this._lastId;
       this._callbacks.set(id, f);
+      this._resetRef();
       this._port.postMessage({ id, method, params });
     });
   }
+
+  private _resetRef() {
+    if (this._callbacks.size) {
+      // When we are waiting for a response, ref the port to prevent this process from exiting.
+      (this._port as any).ref();
+    } else {
+      // When we are not waiting for a response, unref the port to prevent this process
+      // from hanging forever.
+      (this._port as any).unref();
+    }
+  }
 }

tests/playwright-test/clear-cache.spec.ts

@@ -0,0 +1,51 @@
+/**
+ * Copyright Microsoft Corporation. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import { test, expect } from './playwright-test-fixtures';
+import path from 'path';
+
+export const ctReactCliEntrypoint = path.join(__dirname, '../../packages/playwright-ct-react/cli.js');
+
+test('should clear cache with type:module', async ({ runCLICommand }) => {
+  const result = await runCLICommand({
+    'playwright.config.ts': `
+      import { defineConfig } from '@playwright/test';
+      export default defineConfig({});
+    `,
+    'pacakge.json': `
+      { "type": "module" }
+    `,
+    'a.spec.ts': `
+      import { test } from '@playwright/test';
+      test('example', () => {});
+    `,
+  }, 'clear-cache');
+  expect(result.exitCode).toBe(0);
+});
+
+test('should clear cache for ct', async ({ runCLICommand }) => {
+  const result = await runCLICommand({
+    'playwright.config.ts': `
+      import { defineConfig } from '@playwright/test';
+      export default defineConfig({});
+    `,
+    'a.spec.ts': `
+      import { test } from '@playwright/test';
+      test('example', () => {});
+    `,
+  }, 'clear-cache', [], ctReactCliEntrypoint);
+  expect(result.exitCode).toBe(0);
+});