Add platform channel System.exitApplication and System.requestAppExit support (flutter/engine#39836)

Add platform channel `System.exitApplication` and  `System.requestAppExit` support

engine/src/flutter/ci/licenses_golden/licenses_flutter

@@ -2550,6 +2550,7 @@ ORIGIN: ../../../flutter/shell/platform/darwin/ios/platform_view_ios.mm + ../../
 ORIGIN: ../../../flutter/shell/platform/darwin/ios/rendering_api_selection.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/darwin/ios/rendering_api_selection.mm + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/darwin/macos/framework/Headers/FlutterAppDelegate.h + ../../../flutter/LICENSE
+ORIGIN: ../../../flutter/shell/platform/darwin/macos/framework/Headers/FlutterApplication.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/darwin/macos/framework/Headers/FlutterDartProject.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/darwin/macos/framework/Headers/FlutterEngine.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/darwin/macos/framework/Headers/FlutterMacOS.h + ../../../flutter/LICENSE
@@ -2561,6 +2562,9 @@ ORIGIN: ../../../flutter/shell/platform/darwin/macos/framework/Source/Accessibil
 ORIGIN: ../../../flutter/shell/platform/darwin/macos/framework/Source/AccessibilityBridgeMac.mm + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/darwin/macos/framework/Source/AccessibilityBridgeMacTest.mm + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterAppDelegate.mm + ../../../flutter/LICENSE
+ORIGIN: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterAppDelegate_Internal.h + ../../../flutter/LICENSE
+ORIGIN: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterApplication.mm + ../../../flutter/LICENSE
+ORIGIN: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterApplication_Internal.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterBackingStore.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterBackingStore.mm + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterChannelKeyResponder.h + ../../../flutter/LICENSE
@@ -5083,6 +5087,7 @@ FILE: ../../../flutter/shell/platform/darwin/ios/platform_view_ios.mm
 FILE: ../../../flutter/shell/platform/darwin/ios/rendering_api_selection.h
 FILE: ../../../flutter/shell/platform/darwin/ios/rendering_api_selection.mm
 FILE: ../../../flutter/shell/platform/darwin/macos/framework/Headers/FlutterAppDelegate.h
+FILE: ../../../flutter/shell/platform/darwin/macos/framework/Headers/FlutterApplication.h
 FILE: ../../../flutter/shell/platform/darwin/macos/framework/Headers/FlutterDartProject.h
 FILE: ../../../flutter/shell/platform/darwin/macos/framework/Headers/FlutterEngine.h
 FILE: ../../../flutter/shell/platform/darwin/macos/framework/Headers/FlutterMacOS.h
@@ -5095,6 +5100,9 @@ FILE: ../../../flutter/shell/platform/darwin/macos/framework/Source/Accessibilit
 FILE: ../../../flutter/shell/platform/darwin/macos/framework/Source/AccessibilityBridgeMac.mm
 FILE: ../../../flutter/shell/platform/darwin/macos/framework/Source/AccessibilityBridgeMacTest.mm
 FILE: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterAppDelegate.mm
+FILE: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterAppDelegate_Internal.h
+FILE: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterApplication.mm
+FILE: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterApplication_Internal.h
 FILE: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterBackingStore.h
 FILE: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterBackingStore.mm
 FILE: ../../../flutter/shell/platform/darwin/macos/framework/Source/FlutterChannelKeyResponder.h

engine/src/flutter/lib/ui/platform_dispatcher.dart

@@ -1690,6 +1690,43 @@ enum AppLifecycleState {
   detached,
 }
 
+/// The possible responses to a request to exit the application.
+///
+/// The request is typically responded to by a [WidgetsBindingObserver].
+// TODO(gspencergoog): Insert doc references here to AppLifecycleListener and to
+// the actual function called on WidgetsBindingObserver once those have landed
+// in the framework. https://github.com/flutter/flutter/issues/121721
+enum AppExitResponse {
+  /// Exiting the application can proceed.
+  exit,
+  /// Cancel the exit: do not exit the application.
+  cancel,
+}
+
+/// The type of application exit to perform when calling
+/// `ServicesBinding.exitApplication`.
+// TODO(gspencergoog): Insert doc references here to
+// ServicesBinding.exitApplication that has landed in the framework.
+// https://github.com/flutter/flutter/issues/121721
+enum AppExitType {
+  /// Requests that the application start an orderly exit, sending a request
+  /// back to the framework through the [WidgetsBinding]. If that responds
+  /// with [AppExitResponse.exit], then proceed with the same steps as a
+  /// [required] exit. If that responds with [AppExitResponse.cancel], then the
+  /// exit request is canceled and the application continues executing normally.
+  cancelable,
+
+  /// A non-cancelable orderly exit request. The engine will shut down the
+  /// engine and call the native UI toolkit's exit API.
+  ///
+  /// If you need an even faster and more dangerous exit, then call `dart:io`'s
+  /// `exit()` directly, and even the native toolkit's exit API won't be called.
+  /// This is quite dangerous, though, since it's possible that the engine will
+  /// crash because it hasn't been properly shut down, causing the app to crash
+  /// on exit.
+  required,
+}
+
 /// A representation of distances for each of the four edges of a rectangle,
 /// used to encode the view insets and padding that applications should place
 /// around their user interface, as exposed by [FlutterView.viewInsets] and

engine/src/flutter/lib/web_ui/lib/platform_dispatcher.dart

@@ -251,6 +251,16 @@ enum AppLifecycleState {
   detached,
 }
 
+enum AppExitResponse {
+  exit,
+  cancel,
+}
+
+enum AppExitType {
+  cancelable,
+  required,
+}
+
 abstract class ViewPadding {
   const factory ViewPadding._(
       {required double left,

engine/src/flutter/shell/platform/darwin/macos/BUILD.gn

@@ -38,6 +38,7 @@ _framework_binary_subpath = "Versions/A/$_flutter_framework_name"
 # the Flutter engine source root.
 _flutter_framework_headers = [
   "framework/Headers/FlutterAppDelegate.h",
+  "framework/Headers/FlutterApplication.h",
   "framework/Headers/FlutterDartProject.h",
   "framework/Headers/FlutterEngine.h",
   "framework/Headers/FlutterMacOS.h",
@@ -57,6 +58,7 @@ source_set("flutter_framework_source") {
     "framework/Source/AccessibilityBridgeMac.h",
     "framework/Source/AccessibilityBridgeMac.mm",
     "framework/Source/FlutterAppDelegate.mm",
+    "framework/Source/FlutterApplication.mm",
     "framework/Source/FlutterBackingStore.h",
     "framework/Source/FlutterBackingStore.mm",
     "framework/Source/FlutterChannelKeyResponder.h",

engine/src/flutter/shell/platform/darwin/macos/framework/Headers/FlutterApplication.h

@@ -0,0 +1,47 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef FLUTTER_FLUTTERAPPLICATION_H_
+#define FLUTTER_FLUTTERAPPLICATION_H_
+
+#import <Cocoa/Cocoa.h>
+
+/**
+ * A Flutter-specific subclass of NSApplication that overrides |terminate| and
+ * provides an additional |terminateApplication| method so that Flutter can
+ * handle requests for termination in an asynchronous fashion.
+ *
+ * When a call to |terminate| comes in, either from the OS through a Quit menu
+ * item, through the Quit item in the dock context menu, or from the application
+ * itself, a request is sent to the Flutter framework. If that request is
+ * granted, this subclass will (in |terminateApplication|) call
+ * |NSApplication|'s version of |terminate| to proceed with terminating the
+ * application normally by calling |applicationShouldTerminate|, etc.
+ *
+ * If the termination request is denied by the framework, then the application
+ * will continue to execute normally, as if no |terminate| call were made.
+ *
+ * The |FlutterAppDelegate| always returns |NSTerminateNow| from
+ * |applicationShouldTerminate|, since it has already decided by that point that
+ * it should terminate.
+ *
+ * In order for this class to be used in place of |NSApplication|, the
+ * "NSPrincipalClass" entry in the Info.plist for the application must be set to
+ * "FlutterApplication". If it is not, then the application will not be given
+ * the chance to deny a termination request, and calls to requestAppExit on the
+ * engine (from the framework, typically) will simply exit the application
+ * without ceremony.
+ *
+ * If the |NSApp| global isn't of type |FlutterApplication|, a log message will
+ * be printed once in debug mode when the application is first accessed through
+ * the singleton's |sharedApplication|, describing how to fix this.
+ *
+ * Flutter applications are *not* required to inherit from this class.
+ * Developers of custom |NSApplication| subclasses should copy and paste code as
+ * necessary from FlutterApplication.mm.
+ */
+@interface FlutterApplication : NSApplication
+@end
+
+#endif  // FLUTTER_FLUTTERAPPLICATION_H_

engine/src/flutter/shell/platform/darwin/macos/framework/Headers/FlutterMacOS.h

@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 
 #import "FlutterAppDelegate.h"
+#import "FlutterApplication.h"
 #import "FlutterBinaryMessenger.h"
 #import "FlutterChannels.h"
 #import "FlutterCodecs.h"

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

@@ -3,6 +3,12 @@
 // found in the LICENSE file.
 
 #import "flutter/shell/platform/darwin/macos/framework/Headers/FlutterAppDelegate.h"
+#import "flutter/shell/platform/darwin/macos/framework/Source/FlutterAppDelegate_Internal.h"
+
+#import <AppKit/AppKit.h>
+
+#include "flutter/fml/logging.h"
+#include "flutter/shell/platform/embedder/embedder.h"
 
 @interface FlutterAppDelegate ()
 
@@ -15,8 +21,16 @@
 
 @implementation FlutterAppDelegate
 
-// TODO(stuartmorgan): Implement application lifecycle forwarding to plugins here, as is done
+// TODO(gspencergoog): Implement application lifecycle forwarding to plugins here, as is done
 // on iOS. Currently macOS plugins don't have access to lifecycle messages.
+// https://github.com/flutter/flutter/issues/30735
+
+- (instancetype)init {
+  if (self = [super init]) {
+    _terminationHandler = nil;
+  }
+  return self;
+}
 
 - (void)applicationWillFinishLaunching:(NSNotification*)notification {
   // Update UI elements to match the application name.
@@ -28,6 +42,13 @@
   }
 }
 
+// This always returns NSTerminateNow, since by the time we get here, the
+// application has already been asked if it should terminate or not, and if not,
+// then termination never gets this far.
+- (NSApplicationTerminateReply)applicationShouldTerminate:(NSApplication*)sender {
+  return NSTerminateNow;
+}
+
 #pragma mark Private Methods
 
 - (NSString*)applicationName {

engine/src/flutter/shell/platform/darwin/macos/framework/Source/FlutterAppDelegate_Internal.h

@@ -0,0 +1,21 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef FLUTTER_FLUTTERAPPDELEGATE_INTERNAL_H_
+#define FLUTTER_FLUTTERAPPDELEGATE_INTERNAL_H_
+
+#import "flutter/shell/platform/darwin/macos/framework/Headers/FlutterAppDelegate.h"
+#import "flutter/shell/platform/darwin/macos/framework/Source/FlutterEngine_Internal.h"
+
+@interface FlutterAppDelegate ()
+
+/**
+ * Holds a weak reference to the termination handler owned by the engine.
+ * Called by the |FlutterApplication| when termination is requested by the OS.
+ */
+@property(readwrite, nullable, weak) FlutterEngineTerminationHandler* terminationHandler;
+
+@end
+
+#endif  // FLUTTER_FLUTTERAPPDELEGATE_INTERNAL_H_

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

@@ -0,0 +1,90 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#import "flutter/shell/platform/darwin/macos/framework/Headers/FlutterApplication.h"
+#import "flutter/shell/platform/darwin/macos/framework/Source/FlutterApplication_Internal.h"
+
+#include "flutter/shell/platform/embedder/embedder.h"
+#import "shell/platform/darwin/macos/framework/Headers/FlutterAppDelegate.h"
+#import "shell/platform/darwin/macos/framework/Source/FlutterAppDelegate_Internal.h"
+#import "shell/platform/darwin/macos/framework/Source/FlutterEngine_Internal.h"
+
+// An NSApplication subclass that implements overrides necessary for some
+// Flutter features, like application lifecycle handling.
+@implementation FlutterApplication
+
+// Initialize NSApplication using the custom subclass. Check whether NSApp was
+// already initialized using another class, because that would break some
+// things. Warn about the mismatch only once, and only in debug builds.
++ (NSApplication*)sharedApplication {
+  NSApplication* app = [super sharedApplication];
+
+  // +sharedApplication initializes the global NSApp, so if we're delivering
+  // something other than a FlutterApplication, warn the developer once.
+#ifndef FLUTTER_RELEASE
+  static dispatch_once_t onceToken = 0;
+  dispatch_once(&onceToken, ^{
+    if (![app respondsToSelector:@selector(terminateApplication:)]) {
+      NSLog(@"NSApp should be of type %s, not %s.\n"
+             "System requests for the application to terminate will not be sent to "
+             "the Flutter framework, so the framework will be unable to cancel "
+             "those requests.\n"
+             "Modify the application's NSPrincipleClass to be %s in the "
+             "Info.plist to fix this.",
+            [[self className] UTF8String], [[NSApp className] UTF8String],
+            [[self className] UTF8String]);
+    }
+  });
+#endif  // !FLUTTER_RELEASE
+  return app;
+}
+
+// |terminate| is the entry point for orderly "quit" operations in Cocoa. This
+// includes the application menu's Quit menu item and keyboard equivalent, the
+// application's dock icon menu's Quit menu item, "quit" (not "force quit") in
+// the Activity Monitor, and quits triggered by user logout and system restart
+// and shutdown.
+//
+// We override the normal |terminate| implementation. Our implementation, which
+// is specific to the asynchronous nature of Flutter, works by asking the
+// application delegate to terminate using its |requestApplicationTermination|
+// method instead of going through |applicationShouldTerminate|.
+//
+// The standard |applicationShouldTerminate| is not used because returning
+// NSTerminateLater from that function moves the run loop into a modal dialog
+// mode (NSModalPanelRunLoopMode), which stops the main run loop from processing
+// messages like, for instance, the response to the method channel call, and
+// code paths leading to it must be redirected to |requestApplicationTermination|.
+//
+// |requestApplicationTermination| differs from the standard
+// |applicationShouldTerminate| in that no special event loop is run in the case
+// that immediate termination is not possible (e.g., if dialog boxes allowing
+// the user to cancel have to be shown, or data needs to be saved). Instead,
+// requestApplicationTermination sends a method channel call to the framework asking
+// it if it is OK to terminate. When that method channel call returns with a
+// result, the application either terminates or continues running.
+- (void)terminate:(id)sender {
+  FlutterAppDelegate* delegate = [self delegate];
+  if (!delegate || ![delegate respondsToSelector:@selector(terminationHandler)] ||
+      [delegate terminationHandler] == nil) {
+    // If there's no termination handler, then just terminate.
+    [super terminate:sender];
+  }
+  FlutterEngineTerminationHandler* terminationHandler =
+      [static_cast<FlutterAppDelegate*>([self delegate]) terminationHandler];
+  [terminationHandler requestApplicationTermination:sender
+                                           exitType:kFlutterAppExitTypeCancelable
+                                             result:nil];
+  // Return, don't exit. The application delegate is responsible for exiting on
+  // its own by calling |terminateApplication|.
+}
+
+// Starts the regular Cocoa application termination flow, so that plugins will
+// get the appropriate notifications after the application has already decided
+// to quit. This is called after the application has decided that
+// it's OK to terminate.
+- (void)terminateApplication:(id)sender {
+  [super terminate:sender];
+}
+@end

engine/src/flutter/shell/platform/darwin/macos/framework/Source/FlutterApplication_Internal.h

@@ -0,0 +1,27 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef FLUTTER_FLUTTERAPPLICATION_INTERNAL_H_
+#define FLUTTER_FLUTTERAPPLICATION_INTERNAL_H_
+
+#import "flutter/shell/platform/darwin/macos/framework/Headers/FlutterApplication.h"
+
+/**
+ * Define |terminateApplication| for internal use.
+ */
+@interface FlutterApplication ()
+
+/**
+ * FlutterApplication's implementation of |terminate| doesn't terminate the
+ * application: that is left up to the engine, which will call this function if
+ * it decides that termination request is granted, which will start the regular
+ * Cocoa flow for terminating the application, calling
+ * |applicationShouldTerminate|, etc.
+ *
+ * @param(sender) The id of the object requesting the termination, or nil.
+ */
+- (void)terminateApplication:(id)sender;
+@end
+
+#endif  // FLUTTER_FLUTTERAPPLICATION_INTERNAL_H_

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

@@ -10,6 +10,12 @@
 #include <vector>
 
 #include "flutter/shell/platform/common/engine_switches.h"
+#include "flutter/shell/platform/embedder/embedder.h"
+
+#import "flutter/shell/platform/darwin/macos/framework/Headers/FlutterAppDelegate.h"
+#import "flutter/shell/platform/darwin/macos/framework/Headers/FlutterApplication.h"
+#import "flutter/shell/platform/darwin/macos/framework/Source/FlutterAppDelegate_Internal.h"
+#import "flutter/shell/platform/darwin/macos/framework/Source/FlutterApplication_Internal.h"
 #import "flutter/shell/platform/darwin/macos/framework/Source/FlutterCompositor.h"
 #import "flutter/shell/platform/darwin/macos/framework/Source/FlutterDartProject_Internal.h"
 #import "flutter/shell/platform/darwin/macos/framework/Source/FlutterMenuPlugin.h"
@@ -18,10 +24,11 @@
 #import "flutter/shell/platform/darwin/macos/framework/Source/FlutterRenderer.h"
 #import "flutter/shell/platform/darwin/macos/framework/Source/FlutterViewController_Internal.h"
 #import "flutter/shell/platform/darwin/macos/framework/Source/FlutterViewEngineProvider.h"
-#include "flutter/shell/platform/embedder/embedder.h"
 
 const uint64_t kFlutterDefaultViewId = 0;
 
+NSString* const kFlutterPlatformChannel = @"flutter/platform";
+
 /**
  * Constructs and returns a FlutterLocale struct corresponding to |locale|, which must outlive
  * the returned struct.
@@ -152,6 +159,84 @@ constexpr char kTextPlainFormat[] = "text/plain";
 
 #pragma mark -
 
+@implementation FlutterEngineTerminationHandler {
+  FlutterEngine* _engine;
+  FlutterTerminationCallback _terminator;
+}
+
+- (instancetype)initWithEngine:(FlutterEngine*)engine
+                    terminator:(FlutterTerminationCallback)terminator {
+  self = [super init];
+  _engine = engine;
+  _terminator = terminator ? terminator : ^(id sender) {
+    // Default to actually terminating the application. The terminator exists to
+    // allow tests to override it so that an actual exit doesn't occur.
+    FlutterApplication* flutterApp = [FlutterApplication sharedApplication];
+    if (flutterApp && [flutterApp respondsToSelector:@selector(terminateApplication:)]) {
+      [[FlutterApplication sharedApplication] terminateApplication:sender];
+    } else if (flutterApp) {
+      [flutterApp terminate:sender];
+    }
+  };
+  FlutterAppDelegate* appDelegate =
+      (FlutterAppDelegate*)[[FlutterApplication sharedApplication] delegate];
+  appDelegate.terminationHandler = self;
+  return self;
+}
+
+// This is called by the method call handler in the engine when the application
+// requests termination itself.
+- (void)handleRequestAppExitMethodCall:(NSDictionary<NSString*, id>*)arguments
+                                result:(FlutterResult)result {
+  NSString* type = arguments[@"type"];
+  // Ignore the "exitCode" value in the arguments because AppKit doesn't have
+  // any good way to set the process exit code other than calling exit(), and
+  // that bypasses all of the native applicationShouldExit shutdown events,
+  // etc., which we don't want to skip.
+
+  FlutterAppExitType exitType =
+      [type isEqualTo:@"cancelable"] ? kFlutterAppExitTypeCancelable : kFlutterAppExitTypeRequired;
+
+  [self requestApplicationTermination:[FlutterApplication sharedApplication]
+                             exitType:exitType
+                               result:result];
+}
+
+// This is called by the FlutterAppDelegate whenever any termination request is
+// received.
+- (void)requestApplicationTermination:(id)sender
+                             exitType:(FlutterAppExitType)type
+                               result:(nullable FlutterResult)result {
+  switch (type) {
+    case kFlutterAppExitTypeCancelable: {
+      FlutterJSONMethodCodec* codec = [FlutterJSONMethodCodec sharedInstance];
+      FlutterMethodCall* methodCall =
+          [FlutterMethodCall methodCallWithMethodName:@"System.requestAppExit" arguments:nil];
+      [_engine sendOnChannel:kFlutterPlatformChannel
+                     message:[codec encodeMethodCall:methodCall]
+                 binaryReply:^(NSData* _Nullable reply) {
+                   NSDictionary* replyArgs = [codec decodeEnvelope:reply];
+                   if ([replyArgs[@"response"] isEqual:@"exit"]) {
+                     NSAssert(_terminator, @"terminator shouldn't be nil");
+                     _terminator(sender);
+                   }
+                   if (result != nil) {
+                     result(replyArgs);
+                   }
+                 }];
+      break;
+    }
+    case kFlutterAppExitTypeRequired:
+      NSAssert(_terminator, @"terminator shouldn't be nil");
+      _terminator(sender);
+      break;
+  }
+}
+
+@end
+
+#pragma mark -
+
 /**
  * `FlutterPluginRegistrar` implementation handling a single plugin.
  */
@@ -290,6 +375,8 @@ static void OnPlatformMessage(const FlutterPlatformMessage* message, FlutterEngi
   _semanticsEnabled = NO;
   _isResponseValid = [[NSMutableArray alloc] initWithCapacity:1];
   [_isResponseValid addObject:@YES];
+  _terminationHandler = [[FlutterEngineTerminationHandler alloc] initWithEngine:self
+                                                                     terminator:nil];
   // kFlutterDefaultViewId is reserved for the default view.
   // All IDs above it are for regular views.
   _nextViewId = kFlutterDefaultViewId + 1;
@@ -881,6 +968,8 @@ static void OnPlatformMessage(const FlutterPlatformMessage* message, FlutterEngi
     result(nil);
   } else if ([call.method isEqualToString:@"Clipboard.hasStrings"]) {
     result(@{@"value" : @([self clipboardHasStrings])});
+  } else if ([call.method isEqualToString:@"System.exitApplication"]) {
+    [[self terminationHandler] handleRequestAppExitMethodCall:call.arguments result:result];
   } else {
     result(FlutterMethodNotImplemented);
   }

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

@@ -4,6 +4,7 @@
 
 #import "flutter/shell/platform/darwin/macos/framework/Headers/FlutterEngine.h"
 #import "flutter/shell/platform/darwin/macos/framework/Source/FlutterEngine_Internal.h"
+#include "gtest/gtest.h"
 
 #include <functional>
 #include <thread>
@@ -12,6 +13,7 @@
 #include "flutter/lib/ui/window/platform_message.h"
 #include "flutter/shell/platform/common/accessibility_bridge.h"
 #import "flutter/shell/platform/darwin/macos/framework/Headers/FlutterAppDelegate.h"
+#import "flutter/shell/platform/darwin/macos/framework/Headers/FlutterApplication.h"
 #import "flutter/shell/platform/darwin/macos/framework/Source/FlutterEngineTestUtils.h"
 #import "flutter/shell/platform/darwin/macos/framework/Source/FlutterViewControllerTestUtils.h"
 #include "flutter/shell/platform/embedder/embedder.h"
@@ -407,7 +409,7 @@ TEST_F(FlutterEngineTest, NativeCallbacks) {
   ASSERT_TRUE(latch_called);
 }
 
-TEST(FlutterEngine, Compositor) {
+TEST_F(FlutterEngineTest, Compositor) {
   NSString* fixtures = @(flutter::testing::GetFixturesPath());
   FlutterDartProject* project = [[FlutterDartProject alloc]
       initWithAssetsPath:fixtures
@@ -446,7 +448,7 @@ TEST(FlutterEngine, Compositor) {
   [engine shutDownEngine];
 }  // namespace flutter::testing
 
-TEST(FlutterEngine, DartEntrypointArguments) {
+TEST_F(FlutterEngineTest, DartEntrypointArguments) {
   NSString* fixtures = @(flutter::testing::GetFixturesPath());
   FlutterDartProject* project = [[FlutterDartProject alloc]
       initWithAssetsPath:fixtures
@@ -541,7 +543,7 @@ TEST_F(FlutterEngineTest, MessengerCleanupConnectionWorks) {
   EXPECT_EQ(record, 21);
 }
 
-TEST(FlutterEngine, HasStringsWhenPasteboardEmpty) {
+TEST_F(FlutterEngineTest, HasStringsWhenPasteboardEmpty) {
   id engineMock = CreateMockFlutterEngine(nil);
 
   // Call hasStrings and expect it to be false.
@@ -559,7 +561,7 @@ TEST(FlutterEngine, HasStringsWhenPasteboardEmpty) {
   EXPECT_FALSE(valueAfterClear);
 }
 
-TEST(FlutterEngine, HasStringsWhenPasteboardFull) {
+TEST_F(FlutterEngineTest, HasStringsWhenPasteboardFull) {
   id engineMock = CreateMockFlutterEngine(@"some string");
 
   // Call hasStrings and expect it to be true.
@@ -619,7 +621,7 @@ TEST_F(FlutterEngineTest, ResponseFromBackgroundThread) {
   }
 }
 
-TEST(EngineTest, ThreadSynchronizerNotBlockingRasterThreadAfterShutdown) {
+TEST_F(FlutterEngineTest, ThreadSynchronizerNotBlockingRasterThreadAfterShutdown) {
   FlutterThreadSynchronizer* threadSynchronizer = [[FlutterThreadSynchronizer alloc] init];
   [threadSynchronizer shutdown];
 
@@ -695,6 +697,55 @@ TEST_F(FlutterEngineTest, ManageControllersIfInitiatedByEngine) {
   EXPECT_EQ(viewController1.id, 0ull);
 }
 
+TEST_F(FlutterEngineTest, HandlesTerminationRequest) {
+  id engineMock = CreateMockFlutterEngine(nil);
+  __block NSString* nextResponse = @"exit";
+  __block BOOL triedToTerminate = FALSE;
+  FlutterEngineTerminationHandler* terminationHandler =
+      [[FlutterEngineTerminationHandler alloc] initWithEngine:engineMock
+                                                   terminator:^(id sender) {
+                                                     triedToTerminate = TRUE;
+                                                     // Don't actually terminate, of course.
+                                                   }];
+  OCMStub([engineMock terminationHandler]).andReturn(terminationHandler);
+  id binaryMessengerMock = OCMProtocolMock(@protocol(FlutterBinaryMessenger));
+  OCMStub(  // NOLINT(google-objc-avoid-throwing-exception)
+      [engineMock binaryMessenger])
+      .andReturn(binaryMessengerMock);
+  OCMStub([engineMock sendOnChannel:@"flutter/platform"
+                            message:[OCMArg any]
+                        binaryReply:[OCMArg any]])
+      .andDo((^(NSInvocation* invocation) {
+        [invocation retainArguments];
+        FlutterBinaryReply callback;
+        [invocation getArgument:&callback atIndex:4];
+        NSDictionary* responseDict = @{@"response" : nextResponse};
+        NSData* returnedMessage =
+            [[FlutterJSONMethodCodec sharedInstance] encodeSuccessEnvelope:responseDict];
+        callback(returnedMessage);
+      }));
+  __block NSString* calledAfterTerminate = @"";
+  FlutterResult appExitResult = ^(id result) {
+    NSDictionary* resultDict = result;
+    calledAfterTerminate = resultDict[@"response"];
+  };
+  FlutterMethodCall* methodExitApplication =
+      [FlutterMethodCall methodCallWithMethodName:@"System.exitApplication"
+                                        arguments:@{@"type" : @"cancelable"}];
+
+  triedToTerminate = FALSE;
+  nextResponse = @"exit";
+  [engineMock handleMethodCall:methodExitApplication result:appExitResult];
+  EXPECT_STREQ([calledAfterTerminate UTF8String], "exit");
+  EXPECT_TRUE(triedToTerminate);
+
+  triedToTerminate = FALSE;
+  nextResponse = @"cancel";
+  [engineMock handleMethodCall:methodExitApplication result:appExitResult];
+  EXPECT_STREQ([calledAfterTerminate UTF8String], "cancel");
+  EXPECT_FALSE(triedToTerminate);
+}
+
 }  // namespace flutter::testing
 
 // NOLINTEND(clang-analyzer-core.StackAddressEscape)

engine/src/flutter/shell/platform/darwin/macos/framework/Source/FlutterEngine_Internal.h

@@ -8,11 +8,59 @@
 
 #include <memory>
 
+#import "flutter/shell/platform/darwin/macos/framework/Headers/FlutterApplication.h"
 #import "flutter/shell/platform/darwin/macos/framework/Source/AccessibilityBridgeMac.h"
 #import "flutter/shell/platform/darwin/macos/framework/Source/FlutterCompositor.h"
 #import "flutter/shell/platform/darwin/macos/framework/Source/FlutterPlatformViewController.h"
 #import "flutter/shell/platform/darwin/macos/framework/Source/FlutterRenderer.h"
 
+NS_ASSUME_NONNULL_BEGIN
+
+#pragma mark - Typedefs
+
+typedef void (^FlutterTerminationCallback)(id _Nullable sender);
+
+#pragma mark - Enumerations
+
+/**
+ * An enum for defining the different request types allowed when requesting an
+ * application exit.
+ *
+ * Must match the entries in the `AppExitType` enum in the Dart code.
+ */
+typedef NS_ENUM(NSInteger, FlutterAppExitType) {
+  kFlutterAppExitTypeCancelable = 0,
+  kFlutterAppExitTypeRequired = 1,
+};
+
+/**
+ * An enum for defining the different responses the framework can give to an
+ * application exit request from the engine.
+ *
+ * Must match the entries in the `AppExitResponse` enum in the Dart code.
+ */
+typedef NS_ENUM(NSInteger, FlutterAppExitResponse) {
+  kFlutterAppExitResponseCancel = 0,
+  kFlutterAppExitResponseExit = 1,
+};
+
+#pragma mark - FlutterEngineTerminationHandler
+
+/**
+ * A handler interface for handling application termination that the
+ * FlutterAppDelegate can use to coordinate an application exit by sending
+ * messages through the platform channel managed by the engine.
+ */
+@interface FlutterEngineTerminationHandler : NSObject
+- (instancetype)initWithEngine:(FlutterEngine*)engine
+                    terminator:(nullable FlutterTerminationCallback)terminator;
+- (void)handleRequestAppExitMethodCall:(NSDictionary<NSString*, id>*)data
+                                result:(FlutterResult)result;
+- (void)requestApplicationTermination:(FlutterApplication*)sender
+                             exitType:(FlutterAppExitType)type
+                               result:(nullable FlutterResult)result;
+@end
+
 @interface FlutterEngine ()
 
 /**
@@ -52,6 +100,11 @@
  */
 @property(nonatomic, readonly) std::vector<std::string> switches;
 
+/**
+ * Provides the |FlutterEngineTerminationHandler| to be used for this engine.
+ */
+@property(nonatomic, readonly) FlutterEngineTerminationHandler* terminationHandler;
+
 /**
  * Attach a view controller to the engine as its default controller.
  *
@@ -64,7 +117,7 @@
  * If the given view controller is already attached to an engine, this call
  * throws an assertion.
  */
-- (void)addViewController:(nonnull FlutterViewController*)viewController;
+- (void)addViewController:(FlutterViewController*)viewController;
 
 /**
  * Dissociate the given view controller from this engine.
@@ -75,17 +128,17 @@
  * If the view controller is not associated with this engine, this call throws an
  * assertion.
  */
-- (void)removeViewController:(nonnull FlutterViewController*)viewController;
+- (void)removeViewController:(FlutterViewController*)viewController;
 
 /**
- * The `FlutterViewController` associated with the given view ID, if any.
+ * The |FlutterViewController| associated with the given view ID, if any.
  */
 - (nullable FlutterViewController*)viewControllerForId:(uint64_t)viewId;
 
 /**
  * Informs the engine that the specified view controller's window metrics have changed.
  */
-- (void)updateWindowMetricsForViewController:(nonnull FlutterViewController*)viewController;
+- (void)updateWindowMetricsForViewController:(FlutterViewController*)viewController;
 
 /**
  * Dispatches the given pointer event data to engine.
@@ -127,3 +180,5 @@
                        withData:(fml::MallocMapping)data;
 
 @end
+
+NS_ASSUME_NONNULL_END

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

@@ -14,7 +14,6 @@
 #include "flutter/shell/platform/common/text_editing_delta.h"
 #include "flutter/shell/platform/common/text_input_model.h"
 #import "flutter/shell/platform/darwin/common/framework/Headers/FlutterCodecs.h"
-#import "flutter/shell/platform/darwin/macos/framework/Headers/FlutterAppDelegate.h"
 #import "flutter/shell/platform/darwin/macos/framework/Source/FlutterTextInputSemanticsObject.h"
 #import "flutter/shell/platform/darwin/macos/framework/Source/FlutterViewController_Internal.h"
 

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

@@ -9,7 +9,6 @@
 
 #import "flutter/shell/platform/darwin/common/framework/Headers/FlutterChannels.h"
 #import "flutter/shell/platform/darwin/common/framework/Headers/FlutterCodecs.h"
-#import "flutter/shell/platform/darwin/macos/framework/Headers/FlutterAppDelegate.h"
 #import "flutter/shell/platform/darwin/macos/framework/Headers/FlutterEngine.h"
 #import "flutter/shell/platform/darwin/macos/framework/Source/FlutterEngine_Internal.h"
 #import "flutter/shell/platform/darwin/macos/framework/Source/FlutterKeyPrimaryResponder.h"