Only register top level window message listener upon registering service binding (flutter/engine#41733)

Move registering the `WM_CLOSE` message listener in the engine from
initialization to in response to a message sent from `ServiceBinding`
upon its initialization so that we do not intercept window messages when
there is no binding registered.

Addresses https://github.com/flutter/flutter/issues/126033.

## Pre-launch Checklist

- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide] and the [C++,
Objective-C, Java style guides].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [ ] I added new tests to check the change I am making or feature I am
adding, or Hixie said the PR is test-exempt. See [testing the engine]
for instructions on writing and running engine tests.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [ ] I signed the [CLA].
- [x] All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-new channel
on [Discord].

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---------

Co-authored-by: Loïc Sharma <737941+loic-sharma@users.noreply.github.com>

engine/src/flutter/shell/platform/darwin/macos/framework/Source/FlutterEngine.mm

@@ -1031,6 +1031,10 @@ static void OnPlatformMessage(const FlutterPlatformMessage* message, FlutterEngi
     result(@{@"value" : @([self clipboardHasStrings])});
   } else if ([call.method isEqualToString:@"System.exitApplication"]) {
     [[self terminationHandler] handleRequestAppExitMethodCall:call.arguments result:result];
+  } else if ([call.method isEqualToString:@"System.initializationComplete"]) {
+    // TODO(gspencergoog): Handle this message to enable exit message listening.
+    // https://github.com/flutter/flutter/issues/126033
+    result(nil);
   } else {
     result(FlutterMethodNotImplemented);
   }

engine/src/flutter/shell/platform/linux/fl_platform_plugin.cc

@@ -20,6 +20,8 @@ static constexpr char kSetClipboardDataMethod[] = "Clipboard.setData";
 static constexpr char kClipboardHasStringsMethod[] = "Clipboard.hasStrings";
 static constexpr char kExitApplicationMethod[] = "System.exitApplication";
 static constexpr char kRequestAppExitMethod[] = "System.requestAppExit";
+static constexpr char kInitializationCompleteMethod[] =
+    "System.initializationComplete";
 static constexpr char kPlaySoundMethod[] = "SystemSound.play";
 static constexpr char kSystemNavigatorPopMethod[] = "SystemNavigator.pop";
 static constexpr char kTextKey[] = "text";
@@ -335,6 +337,10 @@ static void method_call_cb(FlMethodChannel* channel,
     response = system_sound_play(self, args);
   } else if (strcmp(method, kSystemNavigatorPopMethod) == 0) {
     response = system_navigator_pop(self);
+  } else if (strcmp(method, kInitializationCompleteMethod) == 0) {
+    // TODO(gspencergoog): Handle this message to enable exit message listening.
+    // https://github.com/flutter/flutter/issues/126033
+    response = FL_METHOD_RESPONSE(fl_method_success_response_new(nullptr));
   } else {
     response = FL_METHOD_RESPONSE(fl_method_not_implemented_response_new());
   }

engine/src/flutter/shell/platform/windows/flutter_windows_engine.cc

@@ -778,4 +778,8 @@ void FlutterWindowsEngine::OnDwmCompositionChanged() {
   view_->OnDwmCompositionChanged();
 }
 
+void FlutterWindowsEngine::OnApplicationLifecycleEnabled() {
+  lifecycle_manager_->BeginProcessingClose();
+}
+
 }  // namespace flutter

engine/src/flutter/shell/platform/windows/flutter_windows_engine.h

@@ -269,6 +269,10 @@ class FlutterWindowsEngine {
   // Called when a WM_DWMCOMPOSITIONCHANGED message is received.
   void OnDwmCompositionChanged();
 
+  // Called in response to the framework registering a ServiceBindings.
+  // Registers the top level handler for the WM_CLOSE window message.
+  void OnApplicationLifecycleEnabled();
+
  protected:
   // Creates the keyboard key handler.
   //

engine/src/flutter/shell/platform/windows/flutter_windows_engine_unittests.cc

@@ -657,6 +657,7 @@ TEST_F(FlutterWindowsEngineTest, TestExit) {
   ON_CALL(*handler, IsLastWindowOfProcess).WillByDefault([]() { return true; });
   EXPECT_CALL(*handler, Quit).Times(1);
   modifier.SetLifecycleManager(std::move(handler));
+  engine->OnApplicationLifecycleEnabled();
 
   engine->Run();
 
@@ -693,6 +694,7 @@ TEST_F(FlutterWindowsEngineTest, TestExitCancel) {
   ON_CALL(*handler, IsLastWindowOfProcess).WillByDefault([]() { return true; });
   EXPECT_CALL(*handler, Quit).Times(0);
   modifier.SetLifecycleManager(std::move(handler));
+  engine->OnApplicationLifecycleEnabled();
 
   auto binary_messenger =
       std::make_unique<BinaryMessengerImpl>(engine->messenger());
@@ -753,6 +755,7 @@ TEST_F(FlutterWindowsEngineTest, TestExitSecondCloseMessage) {
                 hwnd, msg, wparam, lparam);
           });
   modifier.SetLifecycleManager(std::move(handler));
+  engine->OnApplicationLifecycleEnabled();
 
   engine->Run();
 
@@ -803,6 +806,7 @@ TEST_F(FlutterWindowsEngineTest, TestExitCloseMultiWindow) {
   // Quit should not be called when there is more than one window.
   EXPECT_CALL(*handler, Quit).Times(0);
   modifier.SetLifecycleManager(std::move(handler));
+  engine->OnApplicationLifecycleEnabled();
 
   engine->Run();
 
@@ -814,5 +818,47 @@ TEST_F(FlutterWindowsEngineTest, TestExitCloseMultiWindow) {
   }
 }
 
+TEST_F(FlutterWindowsEngineTest, LifecycleManagerDisabledByDefault) {
+  FlutterWindowsEngineBuilder builder{GetContext()};
+
+  auto window_binding_handler =
+      std::make_unique<::testing::NiceMock<MockWindowBindingHandler>>();
+  MockFlutterWindowsView view(std::move(window_binding_handler));
+  view.SetEngine(builder.Build());
+  FlutterWindowsEngine* engine = view.GetEngine();
+
+  EngineModifier modifier(engine);
+  modifier.embedder_api().RunsAOTCompiledDartCode = []() { return false; };
+  auto handler = std::make_unique<MockWindowsLifecycleManager>(engine);
+  EXPECT_CALL(*handler, IsLastWindowOfProcess).Times(0);
+  modifier.SetLifecycleManager(std::move(handler));
+
+  engine->window_proc_delegate_manager()->OnTopLevelWindowProc(0, WM_CLOSE, 0,
+                                                               0);
+}
+
+TEST_F(FlutterWindowsEngineTest, EnableApplicationLifecycle) {
+  FlutterWindowsEngineBuilder builder{GetContext()};
+
+  auto window_binding_handler =
+      std::make_unique<::testing::NiceMock<MockWindowBindingHandler>>();
+  MockFlutterWindowsView view(std::move(window_binding_handler));
+  view.SetEngine(builder.Build());
+  FlutterWindowsEngine* engine = view.GetEngine();
+
+  EngineModifier modifier(engine);
+  modifier.embedder_api().RunsAOTCompiledDartCode = []() { return false; };
+  auto handler = std::make_unique<MockWindowsLifecycleManager>(engine);
+  ON_CALL(*handler, IsLastWindowOfProcess).WillByDefault([]() {
+    return false;
+  });
+  EXPECT_CALL(*handler, IsLastWindowOfProcess).Times(1);
+  modifier.SetLifecycleManager(std::move(handler));
+  engine->OnApplicationLifecycleEnabled();
+
+  engine->window_proc_delegate_manager()->OnTopLevelWindowProc(0, WM_CLOSE, 0,
+                                                               0);
+}
+
 }  // namespace testing
 }  // namespace flutter

engine/src/flutter/shell/platform/windows/platform_handler.cc

@@ -23,6 +23,8 @@ static constexpr char kHasStringsClipboardMethod[] = "Clipboard.hasStrings";
 static constexpr char kSetClipboardDataMethod[] = "Clipboard.setData";
 static constexpr char kExitApplicationMethod[] = "System.exitApplication";
 static constexpr char kRequestAppExitMethod[] = "System.requestAppExit";
+static constexpr char kInitializationCompleteMethod[] =
+    "System.initializationComplete";
 static constexpr char kPlaySoundMethod[] = "SystemSound.play";
 
 static constexpr char kExitCodeKey[] = "exitCode";
@@ -495,6 +497,9 @@ void PlatformHandler::HandleMethodCall(
     const rapidjson::Value& sound_type = method_call.arguments()[0];
 
     SystemSoundPlay(sound_type.GetString(), std::move(result));
+  } else if (method.compare(kInitializationCompleteMethod) == 0) {
+    engine_->OnApplicationLifecycleEnabled();
+    result->Success();
   } else {
     result->NotImplemented();
   }

engine/src/flutter/shell/platform/windows/windows_lifecycle_manager.cc

@@ -14,7 +14,7 @@
 namespace flutter {
 
 WindowsLifecycleManager::WindowsLifecycleManager(FlutterWindowsEngine* engine)
-    : engine_(engine) {}
+    : engine_(engine), process_close_(false) {}
 
 WindowsLifecycleManager::~WindowsLifecycleManager() {}
 
@@ -49,6 +49,9 @@ bool WindowsLifecycleManager::WindowProc(HWND hwnd,
     // is, we re-dispatch a new WM_CLOSE message. In order to allow the new
     // message to reach other delegates, we ignore it here.
     case WM_CLOSE: {
+      if (!process_close_) {
+        return false;
+      }
       auto key = std::make_tuple(hwnd, wpar, lpar);
       auto itr = sent_close_messages_.find(key);
       if (itr != sent_close_messages_.end()) {
@@ -156,4 +159,8 @@ bool WindowsLifecycleManager::IsLastWindowOfProcess() {
   return num_windows <= 1;
 }
 
+void WindowsLifecycleManager::BeginProcessingClose() {
+  process_close_ = true;
+}
+
 }  // namespace flutter

engine/src/flutter/shell/platform/windows/windows_lifecycle_manager.h

@@ -37,6 +37,9 @@ class WindowsLifecycleManager {
   // Intercept top level window messages, only paying attention to WM_CLOSE.
   bool WindowProc(HWND hwnd, UINT msg, WPARAM w, LPARAM l, LRESULT* result);
 
+  // Signal to start consuming WM_CLOSE messages.
+  void BeginProcessingClose();
+
  protected:
   // Check the number of top-level windows associated with this process, and
   // return true only if there are 1 or fewer.
@@ -51,6 +54,8 @@ class WindowsLifecycleManager {
   FlutterWindowsEngine* engine_;
 
   std::map<std::tuple<HWND, WPARAM, LPARAM>, int> sent_close_messages_;
+
+  bool process_close_;
 };
 
 }  // namespace flutter