flutter_tool: only enable wasm compile in master channel (#121755)

flutter_tool: only enable wasm compile in master channel

packages/flutter_tools/lib/src/commands/build_web.dart

@@ -43,10 +43,19 @@ class BuildWebCommand extends BuildSubCommand {
             'to view and debug the original source code of a compiled and minified Dart '
             'application.'
     );
-    argParser.addFlag(
-      'wasm',
-      help: 'Compile to WebAssembly rather than Javascript (experimental).'
-    );
+
+    if (featureFlags.isFlutterWebWasmEnabled) {
+      argParser.addFlag(
+        'wasm',
+        help: 'Compile to WebAssembly rather than JavaScript (experimental).',
+      );
+    } else {
+      // Add the flag as hidden. Will give a helpful error message in [runCommand] below.
+      argParser.addFlag(
+        'wasm',
+        hide: true,
+      );
+    }
 
     argParser.addOption('pwa-strategy',
       defaultsTo: kOfflineFirst,
@@ -108,6 +117,12 @@ class BuildWebCommand extends BuildSubCommand {
     if (!featureFlags.isWebEnabled) {
       throwToolExit('"build web" is not currently supported. To enable, run "flutter config --enable-web".');
     }
+
+    final bool wasmRequested = boolArg('wasm')!;
+    if (wasmRequested && !featureFlags.isFlutterWebWasmEnabled) {
+      throwToolExit('Compiling to WebAssembly (wasm) is only available on the master channel.');
+    }
+
     final FlutterProject flutterProject = FlutterProject.current();
     final String target = stringArgDeprecated('target')!;
     final BuildInfo buildInfo = await getBuildInfo();
@@ -146,7 +161,7 @@ class BuildWebCommand extends BuildSubCommand {
       stringArgDeprecated('pwa-strategy')!,
       boolArgDeprecated('source-maps'),
       boolArgDeprecated('native-null-assertions'),
-      boolArgDeprecated('wasm'),
+      wasmRequested,
       baseHref: baseHref,
       dart2jsOptimization: stringArgDeprecated('dart2js-optimization') ?? kDart2jsDefaultOptimizationLevel,
       outputDirectoryPath: outputDirectoryPath,

packages/flutter_tools/lib/src/features.dart

@@ -47,6 +47,9 @@ abstract class FeatureFlags {
   /// Whether fast single widget reloads are enabled.
   bool get isSingleWidgetReloadEnabled => false;
 
+  /// Whether WebAssembly compilation for Flutter Web is enabled.
+  bool get isFlutterWebWasmEnabled => false;
+
   /// Whether a particular feature is enabled for the current channel.
   ///
   /// Prefer using one of the specific getters above instead of this API.
@@ -64,8 +67,14 @@ const List<Feature> allFeatures = <Feature>[
   flutterIOSFeature,
   flutterFuchsiaFeature,
   flutterCustomDevicesFeature,
+  flutterWebWasm,
 ];
 
+/// All current Flutter feature flags that can be configured.
+///
+/// [Feature.configSetting] is not `null`.
+Iterable<Feature> get allConfigurableFeatures => allFeatures.where((Feature feature) => feature.configSetting != null);
+
 /// The [Feature] for flutter web.
 const Feature flutterWebFeature = Feature.fullyEnabled(
   name: 'Flutter for web',
@@ -145,6 +154,16 @@ const Feature singleWidgetReload = Feature(
   ),
 );
 
+/// Enabling WebAssembly compilation from `flutter build web`
+const Feature flutterWebWasm = Feature(
+  name: 'WebAssembly compilation from flutter build web',
+  environmentOverride: 'FLUTTER_WEB_WASM',
+  master: FeatureChannelSetting(
+    available: true,
+    enabledByDefault: true,
+  ),
+);
+
 /// A [Feature] is a process for conditionally enabling tool features.
 ///
 /// All settings are optional, and if not provided will generally default to

packages/flutter_tools/lib/src/flutter_features.dart

@@ -47,6 +47,9 @@ class FlutterFeatureFlags implements FeatureFlags {
   @override
   bool get isSingleWidgetReloadEnabled => isEnabled(singleWidgetReload);
 
+  @override
+  bool get isFlutterWebWasmEnabled => isEnabled(flutterWebWasm);
+
   @override
   bool isEnabled(Feature feature) {
     final String currentChannel = _flutterVersion.channel;

packages/flutter_tools/test/general.shard/features_test.dart

@@ -20,7 +20,7 @@ void main() {
       testConfig = Config.test();
       platform = FakePlatform(environment: <String, String>{});
 
-      for (final Feature feature in allFeatures) {
+      for (final Feature feature in allConfigurableFeatures) {
         testConfig.setValue(feature.configSetting!, false);
       }
 
@@ -81,6 +81,12 @@ void main() {
       expect(featureFlags.isWebEnabled, true);
     });
 
+    testWithoutContext('Flutter web wasm only enable on master', () {
+      expect(flutterWebWasm.getSettingForChannel('master').enabledByDefault, isTrue);
+      expect(flutterWebWasm.getSettingForChannel('beta').enabledByDefault, isFalse);
+      expect(flutterWebWasm.getSettingForChannel('stable').enabledByDefault, isFalse);
+    });
+
     testWithoutContext('Flutter web help string', () {
       expect(flutterWebFeature.generateHelpMessage(),
       'Enable or disable Flutter for web. '

packages/flutter_tools/test/integration.shard/command_output_test.dart

@@ -80,7 +80,7 @@ void main() {
 
     // contains all of the experiments in features.dart
     expect((result.stdout as String).split('\n'), containsAll(<Matcher>[
-      for (final Feature feature in allFeatures)
+      for (final Feature feature in allConfigurableFeatures)
         contains(feature.configSetting),
     ]));
   });

packages/flutter_tools/test/integration.shard/flutter_build_wasm_test.dart

@@ -6,6 +6,7 @@ import 'dart:io';
 
 import 'package:file_testing/file_testing.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
+import 'package:flutter_tools/src/features.dart';
 
 import '../src/common.dart';
 import 'test_utils.dart';
@@ -33,18 +34,24 @@ void main() {
   });
 
   test('building web with --wasm produces expected files', () async {
-    final ProcessResult result = processManager.runSync(<String>[
-      flutterBin,
-      'build',
-      'web',
-      '--wasm',
-    ], workingDirectory: exampleAppDir.path);
+    final ProcessResult result = processManager.runSync(
+      <String>[
+        flutterBin,
+        'build',
+        'web',
+        '--wasm',
+      ],
+      workingDirectory: exampleAppDir.path,
+      environment: <String, String>{
+        flutterWebWasm.environmentOverride!: 'true'
+      },
+    );
     expect(result.exitCode, 0);
 
     final Directory appBuildDir = fileSystem.directory(fileSystem.path.join(
       exampleAppDir.path,
       'build',
-      'web_wasm'
+      'web_wasm',
     ));
     for (final String filename in const <String>[
       'flutter.js',

packages/flutter_tools/test/src/fakes.dart

@@ -413,6 +413,7 @@ class TestFeatureFlags implements FeatureFlags {
     this.isIOSEnabled = true,
     this.isFuchsiaEnabled = false,
     this.areCustomDevicesEnabled = false,
+    this.isFlutterWebWasmEnabled = false,
   });
 
   @override
@@ -442,6 +443,9 @@ class TestFeatureFlags implements FeatureFlags {
   @override
   final bool areCustomDevicesEnabled;
 
+  @override
+  final bool isFlutterWebWasmEnabled;
+
   @override
   bool isEnabled(Feature feature) {
     switch (feature) {