flutter tool: add experimental output during wasm build (#124166)

Author: kevmoo

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

@@ -11,7 +11,7 @@ import '../globals.dart' as globals;
 import '../html_utils.dart';
 import '../project.dart';
 import '../runner/flutter_command.dart'
-    show DevelopmentArtifact, FlutterCommandResult;
+    show DevelopmentArtifact, FlutterCommandResult, FlutterOptions;
 import '../web/compile.dart';
 import 'build.dart';
 
@@ -98,14 +98,14 @@ class BuildWebCommand extends BuildSubCommand {
     if (featureFlags.isFlutterWebWasmEnabled) {
       argParser.addSeparator('Experimental options');
       argParser.addFlag(
-        'wasm',
-        help: 'Compile to WebAssembly rather than JavaScript.',
+        FlutterOptions.kWebWasmFlag,
+        help: 'Compile to WebAssembly rather than JavaScript.\nSee $kWasmPreviewUri for more information.',
         negatable: false,
       );
     } else {
       // Add the flag as hidden. Will give a helpful error message in [runCommand] below.
       argParser.addFlag(
-        'wasm',
+        FlutterOptions.kWebWasmFlag,
         hide: true,
       );
     }
@@ -134,7 +134,7 @@ class BuildWebCommand extends BuildSubCommand {
       throwToolExit('"build web" is not currently supported. To enable, run "flutter config --enable-web".');
     }
 
-    final bool wasmRequested = boolArg('wasm');
+    final bool wasmRequested = boolArg(FlutterOptions.kWebWasmFlag);
     if (wasmRequested && !featureFlags.isFlutterWebWasmEnabled) {
       throwToolExit('Compiling to WebAssembly (wasm) is only available on the master channel.');
     }

packages/flutter_tools/lib/src/runner/flutter_command.dart

@@ -126,6 +126,7 @@ class FlutterOptions {
   static const String kWebBrowserFlag = 'web-browser-flag';
   static const String kWebRendererFlag = 'web-renderer';
   static const String kWebResourcesCdnFlag = 'web-resources-cdn';
+  static const String kWebWasmFlag = 'wasm';
 }
 
 /// flutter command categories for usage.

packages/flutter_tools/lib/src/web/compile.dart

@@ -56,6 +56,15 @@ class WebBuilder {
     bool noFrequencyBasedMinification = false,
     String? outputDirectoryPath,
   }) async {
+    if (isWasm) {
+      globals.logger.printBox(
+        title: 'Experimental feature',
+        '''
+  WebAssembly compilation is experimental.
+  See $kWasmPreviewUri for more information.''',
+      );
+    }
+
     final bool hasWebPlugins =
         (await findPlugins(flutterProject)).any((Plugin p) => p.platforms.containsKey(WebPlugin.kConfigKey));
     final Directory outputDirectory = outputDirectoryPath == null
@@ -165,3 +174,5 @@ const Map<WebRendererMode, Map<NullSafetyMode, HostArtifact>> kDartSdkJsMapArtif
     NullSafetyMode.unsound: HostArtifact.webPrecompiledSdkSourcemaps,
   },
 };
+
+const String kWasmPreviewUri = 'https://flutter.dev/wasm';