Attempt to mitigate flakiness around devtools (#94879)

dev/bots/test.dart

@@ -853,19 +853,7 @@ Future<void> _runFrameworkTests() async {
     if (Directory(pubCache).existsSync()) {
       pubEnvironment['PUB_CACHE'] = pubCache;
     }
-
-    // If an existing env variable exists append to it, but only if
-    // it doesn't appear to already include enable-asserts.
-    String toolsArgs = Platform.environment['FLUTTER_TOOL_ARGS'] ?? '';
-    if (!toolsArgs.contains('--enable-asserts')) {
-      toolsArgs += ' --enable-asserts';
-    }
-    pubEnvironment['FLUTTER_TOOL_ARGS'] = toolsArgs.trim();
-    // The flutter_tool will originally have been snapshotted without asserts.
-    // We need to force it to be regenerated with them enabled.
-    deleteFile(path.join(flutterRoot, 'bin', 'cache', 'flutter_tools.snapshot'));
-    deleteFile(path.join(flutterRoot, 'bin', 'cache', 'flutter_tools.stamp'));
-
+    recompileFlutterToolWithAsserts(pubEnvironment);
     await runCommand(
       pub,
       args,
@@ -1536,6 +1524,10 @@ Future<void> _runWebDebugTest(String target, {
 }) async {
   final String testAppDirectory = path.join(flutterRoot, 'dev', 'integration_tests', 'web');
   bool success = false;
+  final Map<String, String> environment = <String, String>{
+    'FLUTTER_WEB': 'true',
+  };
+  recompileFlutterToolWithAsserts(environment);
   final CommandResult result = await runCommand(
     flutter,
     <String>[
@@ -1565,9 +1557,7 @@ Future<void> _runWebDebugTest(String target, {
       }
     },
     workingDirectory: testAppDirectory,
-    environment: <String, String>{
-      'FLUTTER_WEB': 'true',
-    },
+    environment: environment,
   );
 
   if (success) {
@@ -1663,16 +1653,7 @@ Future<void> _pubRunTest(String workingDirectory, {
     pubEnvironment['PUB_CACHE'] = pubCache;
   }
   if (enableFlutterToolAsserts) {
-    // If an existing env variable exists append to it, but only if
-    // it doesn't appear to already include enable-asserts.
-    String toolsArgs = Platform.environment['FLUTTER_TOOL_ARGS'] ?? '';
-    if (!toolsArgs.contains('--enable-asserts'))
-      toolsArgs += ' --enable-asserts';
-    pubEnvironment['FLUTTER_TOOL_ARGS'] = toolsArgs.trim();
-    // The flutter_tool will originally have been snapshotted without asserts.
-    // We need to force it to be regenerated with them enabled.
-    deleteFile(path.join(flutterRoot, 'bin', 'cache', 'flutter_tools.snapshot'));
-    deleteFile(path.join(flutterRoot, 'bin', 'cache', 'flutter_tools.stamp'));
+    recompileFlutterToolWithAsserts(pubEnvironment);
   }
   if (ensurePrecompiledTool) {
     // We rerun the `flutter` tool here just to make sure that it is compiled
@@ -1800,6 +1781,22 @@ Future<void> _runFlutterTest(String workingDirectory, {
   }
 }
 
+/// This will force the next run of the Flutter tool (if it uses the provided environment) to
+/// have asserts enabled, by setting an environment variable and deleting the cache.
+void recompileFlutterToolWithAsserts(Map<String, String> pubEnvironment) {
+  // If an existing env variable exists append to it, but only if
+  // it doesn't appear to already include enable-asserts.
+  String toolsArgs = Platform.environment['FLUTTER_TOOL_ARGS'] ?? '';
+  if (!toolsArgs.contains('--enable-asserts')) {
+    toolsArgs += ' --enable-asserts';
+  }
+  pubEnvironment['FLUTTER_TOOL_ARGS'] = toolsArgs.trim();
+  // The flutter_tool will originally have been snapshotted without asserts.
+  // We need to force it to be regenerated with them enabled.
+  deleteFile(path.join(flutterRoot, 'bin', 'cache', 'flutter_tools.snapshot'));
+  deleteFile(path.join(flutterRoot, 'bin', 'cache', 'flutter_tools.stamp'));
+}
+
 Map<String, String> _initGradleEnvironment() {
   final String? androidSdkRoot = (Platform.environment['ANDROID_HOME']?.isEmpty ?? true)
       ? Platform.environment['ANDROID_SDK_ROOT']

packages/flutter_tools/lib/src/resident_devtools_handler.dart

@@ -60,7 +60,10 @@ class FlutterResidentDevtoolsHandler implements ResidentDevtoolsHandler {
   bool launchedInBrowser = false;
 
   @override
-  DevToolsServerAddress get activeDevToolsServer => _devToolsLauncher?.activeDevToolsServer;
+  DevToolsServerAddress get activeDevToolsServer {
+    assert(!_readyToAnnounce || _devToolsLauncher?.activeDevToolsServer != null);
+    return _devToolsLauncher?.activeDevToolsServer;
+  }
 
   @override
   bool get readyToAnnounce => _readyToAnnounce;
@@ -72,6 +75,7 @@ class FlutterResidentDevtoolsHandler implements ResidentDevtoolsHandler {
     Uri devToolsServerAddress,
     @required List<FlutterDevice> flutterDevices,
   }) async {
+    assert(!_readyToAnnounce);
     if (!_residentRunner.supportsServiceProtocol || _devToolsLauncher == null) {
       return;
     }
@@ -82,14 +86,20 @@ class FlutterResidentDevtoolsHandler implements ResidentDevtoolsHandler {
       _served = true;
     }
     await _devToolsLauncher.ready;
-    // Do not attempt to print debugger list if the connection has failed.
-    if (_devToolsLauncher.activeDevToolsServer == null) {
+    // Do not attempt to print debugger list if the connection has failed or if we're shutting down.
+    if (_devToolsLauncher.activeDevToolsServer == null || _shutdown) {
+      assert(!_readyToAnnounce);
       return;
     }
     final List<FlutterDevice> devicesWithExtension = await _devicesWithExtensions(flutterDevices);
     await _maybeCallDevToolsUriServiceExtension(devicesWithExtension);
     await _callConnectedVmServiceUriExtension(devicesWithExtension);
+    if (_shutdown) {
+      // If we're shutting down, no point reporting the debugger list.
+      return;
+    }
     _readyToAnnounce = true;
+    assert(_devToolsLauncher.activeDevToolsServer != null);
     if (_residentRunner.reportedDebuggers) {
       // Since the DevTools only just became available, we haven't had a chance to
       // report their URLs yet. Do so now.
@@ -248,6 +258,7 @@ class FlutterResidentDevtoolsHandler implements ResidentDevtoolsHandler {
       return;
     }
     _shutdown = true;
+    _readyToAnnounce = false;
     await _devToolsLauncher.close();
   }
 }