During hot-restart, wait to run main when pause_isolates_on_start is true (#2378)

Author: elliette

dwds/CHANGELOG.md

@@ -3,6 +3,7 @@
 - Rename `dart_library.js` to `ddc_module_loader.js` to match SDK naming changes. - [#2360](https://github.com/dart-lang/webdev/pull/2360)
 - Implement `setFlag` when it is called with `pause_isolates_on_start`. - [#2373](https://github.com/dart-lang/webdev/pull/2373)
 - Do not persist breakpoints across hot restarts or page reloads. - [#2371](https://github.com/dart-lang/webdev/pull/2371)
+- If `pause_isolates_on_start` is `true`, wait for `resume` to run the app's `main` method. - [#2378](https://github.com/dart-lang/webdev/pull/2378)
 
 ## 23.3.0
 

dwds/lib/src/dwds_vm_client.dart

@@ -9,6 +9,7 @@ import 'package:dwds/src/events.dart';
 import 'package:dwds/src/services/chrome_debug_exception.dart';
 import 'package:dwds/src/services/chrome_proxy_service.dart';
 import 'package:dwds/src/services/debug_service.dart';
+import 'package:dwds/src/utilities/shared.dart';
 import 'package:dwds/src/utilities/synchronized.dart';
 import 'package:logging/logging.dart';
 import 'package:uuid/uuid.dart';
@@ -252,11 +253,19 @@ Future<Map<String, dynamic>> _hotRestart(
   // restart. Only return success after the isolate has fully started.
   final stream = chromeProxyService.onEvent('Isolate');
   try {
+    // If we should pause isolates on start, then only run main once we get a
+    // resume event.
+    final pauseIsolatesOnStart = chromeProxyService.pauseIsolatesOnStart;
+    if (pauseIsolatesOnStart) {
+      _waitForResumeEventToRunMain(chromeProxyService);
+    }
     // Generate run id to hot restart all apps loaded into the tab.
     final runId = const Uuid().v4().toString();
     _logger.info('Issuing \$dartHotRestartDwds request');
-    await chromeProxyService.inspector
-        .jsEvaluate('\$dartHotRestartDwds(\'$runId\');', awaitPromise: true);
+    await chromeProxyService.inspector.jsEvaluate(
+      '\$dartHotRestartDwds(\'$runId\', $pauseIsolatesOnStart);',
+      awaitPromise: true,
+    );
     _logger.info('\$dartHotRestartDwds request complete.');
   } on WipError catch (exception) {
     final code = exception.error?['code'];
@@ -289,6 +298,26 @@ Future<Map<String, dynamic>> _hotRestart(
   return {'result': Success().toJson()};
 }
 
+void _waitForResumeEventToRunMain(
+  ChromeProxyService chromeProxyService,
+) {
+  final issuedReadyToRunMainCompleter = Completer<void>();
+
+  final resumeEventsSubscription =
+      chromeProxyService.resumeAfterHotRestartEventsStream.listen((_) async {
+    await chromeProxyService.inspector.jsEvaluate('\$dartReadyToRunMain();');
+    if (!issuedReadyToRunMainCompleter.isCompleted) {
+      issuedReadyToRunMainCompleter.complete();
+    }
+  });
+
+  safeUnawaited(
+    issuedReadyToRunMainCompleter.future.then((_) {
+      resumeEventsSubscription.cancel();
+    }),
+  );
+}
+
 Future<Map<String, dynamic>> _fullReload(
   ChromeProxyService chromeProxyService,
 ) async {