[web] Reland - Switch flutter tool web-renderer default for web to auto (#73595)

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

diff --git a/packages/flutter_tools/lib/src/runner/flutter_command.dart b/packages/flutter_tools/lib/src/runner/flutter_command.dart
index 5c63e61..bf4247a 100644
--- a/packages/flutter_tools/lib/src/runner/flutter_command.dart
+++ b/packages/flutter_tools/lib/src/runner/flutter_command.dart
@@ -461,7 +461,7 @@
 
   void usesWebRendererOption() {
     argParser.addOption('web-renderer',
-      defaultsTo: 'html',
+      defaultsTo: 'auto',
       allowed: <String>['auto', 'canvaskit', 'html'],
       help: 'The renderer implementation to use when building for the web. Possible values are:\n'
             'html - always use the HTML renderer. This renderer uses a combination of HTML, CSS, SVG, 2D Canvas, and WebGL. This is the default.\n'
@@ -902,7 +902,7 @@
         ? stringsArg(FlutterOptions.kDartDefinesOption)
         : <String>[];
 
-    if (argParser.options.containsKey('web-renderer') && argResults.wasParsed('web-renderer')) {
+    if (argParser.options.containsKey('web-renderer')) {
       dartDefines = updateDartDefines(dartDefines, stringArg('web-renderer'));
     }
 

packages/flutter_tools/test/commands.shard/hermetic/build_web_test.dart

diff --git a/packages/flutter_tools/test/commands.shard/hermetic/build_web_test.dart b/packages/flutter_tools/test/commands.shard/hermetic/build_web_test.dart
index ec9a0bf..7f2178f 100644
--- a/packages/flutter_tools/test/commands.shard/hermetic/build_web_test.dart
+++ b/packages/flutter_tools/test/commands.shard/hermetic/build_web_test.dart
@@ -11,6 +11,7 @@
 import 'package:flutter_tools/src/cache.dart';
 import 'package:flutter_tools/src/commands/build.dart';
 import 'package:flutter_tools/src/commands/build_web.dart';
+import 'package:flutter_tools/src/runner/flutter_command.dart';
 import 'package:flutter_tools/src/dart/pub.dart';
 import 'package:flutter_tools/src/features.dart';
 import 'package:flutter_tools/src/globals.dart' as globals;
@@ -97,59 +98,7 @@
   testUsingContext('Builds a web bundle - end to end', () async {
     final BuildCommand buildCommand = BuildCommand();
     final CommandRunner<void> runner = createTestCommandRunner(buildCommand);
-    final List<String> dependencies = <String>[
-      fileSystem.path.join('packages', 'flutter_tools', 'lib', 'src', 'build_system', 'targets', 'web.dart'),
-      fileSystem.path.join('bin', 'cache', 'flutter_web_sdk'),
-      fileSystem.path.join('bin', 'cache', 'dart-sdk', 'bin', 'snapshots', 'dart2js.dart.snapshot'),
-      fileSystem.path.join('bin', 'cache', 'dart-sdk', 'bin', 'dart'),
-      fileSystem.path.join('bin', 'cache', 'dart-sdk '),
-    ];
-    for (final String dependency in dependencies) {
-      fileSystem.file(dependency).createSync(recursive: true);
-    }
-
-    // Project files.
-    fileSystem.file('.packages')
-      .writeAsStringSync('''
-foo:lib/
-fizz:bar/lib/
-''');
-    fileSystem.file('pubspec.yaml')
-      .writeAsStringSync('''
-name: foo
-
-dependencies:
-  flutter:
-    sdk: flutter
-  fizz:
-    path:
-      bar/
-''');
-    fileSystem.file(fileSystem.path.join('bar', 'pubspec.yaml'))
-      ..createSync(recursive: true)
-      ..writeAsStringSync('''
-name: bar
-
-flutter:
-  plugin:
-    platforms:
-      web:
-        pluginClass: UrlLauncherPlugin
-        fileName: url_launcher_web.dart
-''');
-    fileSystem.file(fileSystem.path.join('bar', 'lib', 'url_launcher_web.dart'))
-      ..createSync(recursive: true)
-      ..writeAsStringSync('''
-class UrlLauncherPlugin {}
-''');
-    fileSystem.file(fileSystem.path.join('lib', 'main.dart'))
-      .writeAsStringSync('void main() { }');
-
-    // Process calls. We're not testing that these invocations are correct because
-    // that is covered in targets/web_test.dart.
-    when(globals.buildSystem.build(any, any)).thenAnswer((Invocation invocation) async {
-      return BuildResult(success: true);
-    });
+    setupFileSystemForEndToEndTest(fileSystem);
     await runner.run(<String>['build', 'web']);
 
     expect(fileSystem.file(fileSystem.path.join('lib', 'generated_plugin_registrant.dart')).existsSync(), true);
@@ -181,7 +130,98 @@
     Pub: () => MockPub(),
     ProcessManager: () => FakeProcessManager.any(),
   });
+
+  testUsingContext('Defaults to web renderer auto mode when no option is specified', () async {
+    final TestWebBuildCommand buildCommand = TestWebBuildCommand();
+    final CommandRunner<void> runner = createTestCommandRunner(buildCommand);
+    setupFileSystemForEndToEndTest(fileSystem);
+    await runner.run(<String>['build', 'web']);
+    final BuildInfo buildInfo =
+        await buildCommand.webCommand.getBuildInfo(forcedBuildMode: BuildMode.debug);
+    expect(buildInfo.dartDefines, contains('FLUTTER_WEB_AUTO_DETECT=true'));
+  }, overrides: <Type, Generator>{
+    Platform: () => fakePlatform,
+    FileSystem: () => fileSystem,
+    FeatureFlags: () => TestFeatureFlags(isWebEnabled: true),
+    Pub: () => MockPub(),
+    ProcessManager: () => FakeProcessManager.any(),
+    BuildSystem: () => MockBuildSystem(),
+  });
+}
+
+void setupFileSystemForEndToEndTest(FileSystem fileSystem) {
+  final List<String> dependencies = <String>[
+    fileSystem.path.join('packages', 'flutter_tools', 'lib', 'src', 'build_system', 'targets', 'web.dart'),
+    fileSystem.path.join('bin', 'cache', 'flutter_web_sdk'),
+    fileSystem.path.join('bin', 'cache', 'dart-sdk', 'bin', 'snapshots', 'dart2js.dart.snapshot'),
+    fileSystem.path.join('bin', 'cache', 'dart-sdk', 'bin', 'dart'),
+    fileSystem.path.join('bin', 'cache', 'dart-sdk '),
+  ];
+  for (final String dependency in dependencies) {
+    fileSystem.file(dependency).createSync(recursive: true);
+  }
+
+  // Project files.
+  fileSystem.file('.packages')
+      .writeAsStringSync('''
+foo:lib/
+fizz:bar/lib/
+''');
+  fileSystem.file('pubspec.yaml')
+      .writeAsStringSync('''
+name: foo
+
+dependencies:
+  flutter:
+    sdk: flutter
+  fizz:
+    path:
+      bar/
+''');
+  fileSystem.file(fileSystem.path.join('bar', 'pubspec.yaml'))
+    ..createSync(recursive: true)
+    ..writeAsStringSync('''
+name: bar
+
+flutter:
+  plugin:
+    platforms:
+      web:
+        pluginClass: UrlLauncherPlugin
+        fileName: url_launcher_web.dart
+''');
+  fileSystem.file(fileSystem.path.join('bar', 'lib', 'url_launcher_web.dart'))
+    ..createSync(recursive: true)
+    ..writeAsStringSync('''
+class UrlLauncherPlugin {}
+''');
+  fileSystem.file(fileSystem.path.join('lib', 'main.dart'))
+      .writeAsStringSync('void main() { }');
+
+  // Process calls. We're not testing that these invocations are correct because
+  // that is covered in targets/web_test.dart.
+  when(globals.buildSystem.build(any, any)).thenAnswer((Invocation invocation) async {
+    return BuildResult(success: true);
+  });
 }
 
 class MockBuildSystem extends Mock implements BuildSystem {}
 class MockPub extends Mock implements Pub {}
+
+class TestWebBuildCommand extends FlutterCommand {
+  TestWebBuildCommand({ bool verboseHelp = false }) :
+    webCommand = BuildWebCommand(verboseHelp: verboseHelp) {
+    addSubcommand(webCommand);
+  }
+
+  final BuildWebCommand webCommand;
+
+  @override
+  final String name = 'build';
+
+  @override
+  final String description = 'Build a test executable app.';
+
+  @override
+  Future<FlutterCommandResult> runCommand() async => null;
+}