flutter · loic-sharma · May 17, 2025 · Jul 16, 2025 · Jul 16, 2025 · justinmc
diff --git a/dev/devicelab/lib/tasks/integration_tests.dart b/dev/devicelab/lib/tasks/integration_tests.dart
@@ -189,13 +189,14 @@ TaskFunction dartDefinesTask() {
 }
 
 TaskFunction featureFlagsTask() {
-  return DriverTest(
-    '${flutterDirectory.path}/dev/integration_tests/ui',
-    'lib/feature_flags.dart',
-    // TODO(loic-sharma): Turn on a framework feature flag once one exists.
-    // https://github.com/flutter/flutter/issues/167668
-    environment: const <String, String>{},
-  ).call;
+  return () async {
+    await flutter('config', options: const <String>['--enable-multi-window']);
+
+    return DriverTest(
+      '${flutterDirectory.path}/dev/integration_tests/ui',
+      'lib/feature_flags.dart',
+    ).call();
+  };
 }
 
 TaskFunction createEndToEndIntegrationTest() {

diff --git a/dev/integration_tests/ui/test_driver/feature_flags_test.dart b/dev/integration_tests/ui/test_driver/feature_flags_test.dart
@@ -17,8 +17,6 @@ void main() {
   });
 
   test('Can run with feature flags enabled', () async {
-    // TODO(loic-sharma): Turn on a framework feature flag once one exists.
-    // https://github.com/flutter/flutter/issues/167668
-    await driver?.waitFor(find.text('Feature flags: "{}"'));
+    await driver?.waitFor(find.text('Feature flags: "{multi_window}"'));
   }, timeout: Timeout.none);
 }
diff --git a/packages/flutter/lib/src/foundation/_features.dart b/packages/flutter/lib/src/foundation/_features.dart
@@ -4,6 +4,21 @@
 
 import 'package:meta/meta.dart';
 
+/// Whether the multi-window feature is enabled for the current
+/// application.
+///
+/// Do not use this API. Flutter will make breaking changes
+/// to this API, even in patch versions.
+///
+/// If this returns `false`, `@internal` APIs in the following
+/// files will throw an `UnsupportedError`:
+///
+/// 1. packages/flutter/lib/src/widgets/_windowing.dart
+///
+/// See: https://github.com/flutter/flutter/issues/30701.
+@internal
+bool isWindowingEnabled = debugEnabledFeatureFlags.contains('multi_window');
+
 /// The feature flags this app was built with.
 ///
 /// Do not use this API. Flutter can and will make breaking changes to this API.

diff --git a/packages/flutter/lib/src/material/dialog.dart b/packages/flutter/lib/src/material/dialog.dart
@@ -14,6 +14,8 @@ import 'dart:ui' show SemanticsRole, clampDouble, lerpDouble;
 
 import 'package:flutter/cupertino.dart';
 
+import '../foundation/_features.dart';
+import '../widgets/_windowing.dart';
 import 'color_scheme.dart';
 import 'colors.dart';
 import 'debug.dart';
@@ -275,6 +277,11 @@ class Dialog extends StatelessWidget {
 
     Widget dialogChild;
 
+    if (isWindowingEnabled) {
+      // TODO(team-desktop): Use a window if necessary.
+      createWindow();
+    }
+
     if (_fullscreen) {
       dialogChild = Material(
         color: backgroundColor ?? dialogTheme.backgroundColor ?? defaults.backgroundColor,

diff --git a/packages/flutter/lib/src/widgets/_windowing.dart b/packages/flutter/lib/src/widgets/_windowing.dart
@@ -0,0 +1,66 @@
+// Copyright 2014 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.
+
+// Do not import this file in production applications or packages published
+// to pub.dev. Flutter will make breaking changes to this file, even in patch
+// versions.
+//
+// All APIs in this file must be private or must:
+//
+// 1. Have the `@internal` attribute.
+// 2. Throw an  `UnsupportedError` if `isWindowingEnabled`
+//    is `false.
+//
+// See: https://github.com/flutter/flutter/issues/30701.
+
+import 'package:flutter/foundation.dart';
+
+import '../foundation/_features.dart';
+
+/// Create a new window.
+///
+/// {@template flutter.widgets.windowing.experimental}
+/// Do not use this API in production applications or packages published to
+/// pub.dev. Flutter will make breaking changes to this API, even in patch
+/// versions.
+///
+/// This API throws an [UnsupportedError] error unless Flutter’s windowing
+/// feature is enabled by [isWindowingEnabled].
+///
+/// See: https://github.com/flutter/flutter/issues/30701.
+/// {@endtemplate}
+@internal
+void createWindow() {
+  _throwIfWindowingDisabled();
+
+  // TODO(team-windows): Add logic.
+}
+
+/// Resize a window.
+///
+/// {@macro flutter.widgets.windowing.experimental}
+@internal
+void resizeWindow() {
+  _throwIfWindowingDisabled();
+
+  // TODO(team-windows): Add logic.
+}
+
+void _throwIfWindowingDisabled() {
+  if (!isWindowingEnabled) {
+    throw UnsupportedError('''
+Windowing APIs are not enabled.
+
+Windowing APIs are currently experimental. Do not use windowing APIs in
+production applications or plugins published to pub.dev.
+
+To try experimental windowing APIs:
+
+1. Switch to Flutter's main release channel.
+2. Turn on the multi-window feature flag.
+
+See: https://github.com/flutter/flutter/issues/30701.
+''');
+  }
+}
diff --git a/packages/flutter_tools/lib/src/features.dart b/packages/flutter_tools/lib/src/features.dart
@@ -64,6 +64,9 @@ abstract class FeatureFlags {
   /// Tracking removal: <https://github.com/flutter/flutter/issues/171900>.
   bool get isOmitLegacyVersionFileEnabled;
 
+  /// Whether desktop multi-window is enabled.
+  bool get isMultiWindowEnabled;
+
   /// Whether a particular feature is enabled for the current channel.
   ///
   /// Prefer using one of the specific getters above instead of this API.
@@ -83,6 +86,7 @@ abstract class FeatureFlags {
     nativeAssets,
     swiftPackageManager,
     omitLegacyVersionFile,
+    multiWindowFeature,
   ];
 
   /// All current Flutter feature flags that can be configured.
@@ -203,6 +207,17 @@ const omitLegacyVersionFile = Feature(
   stable: FeatureChannelSetting(available: true),
 );
 
+/// Whether desktop multi-window is enabled.
+///
+/// See: https://github.com/flutter/flutter/issues/30701.
+const multiWindowFeature = Feature(
+  name: 'support for multi-window on macOS, Linux, and Windows',
+  configSetting: 'enable-multi-window',
+  environmentOverride: 'FLUTTER_MULTI_WINDOW',
+  runtimeId: 'multi_window',
+  master: FeatureChannelSetting(available: true),
+);
+
 /// A [Feature] is a process for conditionally enabling tool features.
 ///
 /// All settings are optional, and if not provided will generally default to

diff --git a/packages/flutter_tools/lib/src/flutter_features.dart b/packages/flutter_tools/lib/src/flutter_features.dart
@@ -54,6 +54,9 @@ mixin FlutterFeatureFlagsIsEnabled implements FeatureFlags {
 
   @override
   bool get isOmitLegacyVersionFileEnabled => isEnabled(omitLegacyVersionFile);
+
+  @override
+  bool get isMultiWindowEnabled => isEnabled(multiWindowFeature);
 }
 
 interface class FlutterFeatureFlags extends FeatureFlags with FlutterFeatureFlagsIsEnabled {

diff --git a/packages/flutter_tools/test/general.shard/flutter_validator_test.dart b/packages/flutter_tools/test/general.shard/flutter_validator_test.dart
@@ -815,6 +815,9 @@ class FakeFlutterFeatures extends FeatureFlags {
   @override
   bool get isOmitLegacyVersionFileEnabled => _enabled;
 
+  @override
+  bool get isMultiWindowEnabled => _enabled;
+
   @override
   final List<Feature> allFeatures;
 

diff --git a/packages/flutter_tools/test/src/fakes.dart b/packages/flutter_tools/test/src/fakes.dart
@@ -502,6 +502,7 @@ class TestFeatureFlags implements FeatureFlags {
     this.isNativeAssetsEnabled = false,
     this.isSwiftPackageManagerEnabled = false,
     this.isOmitLegacyVersionFileEnabled = false,
+    this.isMultiWindowEnabled = false,
   });
 
   @override
@@ -540,6 +541,9 @@ class TestFeatureFlags implements FeatureFlags {
   @override
   final bool isOmitLegacyVersionFileEnabled;
 
+  @override
+  final bool isMultiWindowEnabled;
+
   @override
   bool isEnabled(Feature feature) {
     return switch (feature) {
@@ -554,6 +558,7 @@ class TestFeatureFlags implements FeatureFlags {
       cliAnimation => isCliAnimationEnabled,
       nativeAssets => isNativeAssetsEnabled,
       omitLegacyVersionFile => isOmitLegacyVersionFileEnabled,
+      multiWindowFeature => isMultiWindowEnabled,
       _ => false,
     };
   }
@@ -572,6 +577,7 @@ class TestFeatureFlags implements FeatureFlags {
     nativeAssets,
     swiftPackageManager,
     omitLegacyVersionFile,
+    multiWindowFeature,
   ];
 
   @override