Migrate AppBar to Material 3 (#101884)

Author: darrenaustin

dev/tools/gen_defaults/bin/gen_defaults.dart

@@ -17,6 +17,7 @@
 import 'dart:convert';
 import 'dart:io';
 
+import 'package:gen_defaults/app_bar_template.dart';
 import 'package:gen_defaults/button_template.dart';
 import 'package:gen_defaults/card_template.dart';
 import 'package:gen_defaults/dialog_template.dart';
@@ -78,6 +79,7 @@ Future<void> main(List<String> args) async {
   tokens['colorsLight'] = _readTokenFile('color_light.json');
   tokens['colorsDark'] = _readTokenFile('color_dark.json');
 
+  AppBarTemplate('$materialLib/app_bar.dart', tokens).updateFile();
   ButtonTemplate('md.comp.elevated-button', '$materialLib/elevated_button.dart', tokens).updateFile();
   ButtonTemplate('md.comp.outlined-button', '$materialLib/outlined_button.dart', tokens).updateFile();
   ButtonTemplate('md.comp.text-button', '$materialLib/text_button.dart', tokens).updateFile();

dev/tools/gen_defaults/lib/app_bar_template.dart

@@ -0,0 +1,58 @@
+// 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.
+
+import 'template.dart';
+
+class AppBarTemplate extends TokenTemplate {
+  const AppBarTemplate(super.fileName, super.tokens)
+    : super(
+      colorSchemePrefix: '_colors.',
+      textThemePrefix: '_textTheme.',
+    );
+
+  @override
+  String generate() => '''
+// Generated version ${tokens["version"]}
+class _TokenDefaultsM3 extends AppBarTheme {
+  _TokenDefaultsM3(this.context)
+    : super(
+      elevation: ${elevation('md.comp.top-app-bar.small.container')},
+      scrolledUnderElevation: ${elevation('md.comp.top-app-bar.small.on-scroll.container')},
+      titleSpacing: NavigationToolbar.kMiddleSpacing,
+      toolbarHeight: ${tokens['md.comp.top-app-bar.small.container.height']},
+    );
+
+  final BuildContext context;
+  late final ThemeData _theme = Theme.of(context);
+  late final ColorScheme _colors = _theme.colorScheme;
+  late final TextTheme _textTheme = _theme.textTheme;
+
+  @override
+  Color? get backgroundColor => ${componentColor('md.comp.top-app-bar.small.container')};
+
+  @override
+  Color? get foregroundColor => ${color('md.comp.top-app-bar.small.headline.color')};
+
+  @override
+  Color? get surfaceTintColor => ${componentColor('md.comp.top-app-bar.small.container.surface-tint-layer')};
+
+  @override
+  IconThemeData? get iconTheme => IconThemeData(
+    color: ${componentColor('md.comp.top-app-bar.small.leading-icon')},
+    size: ${tokens['md.comp.top-app-bar.small.leading-icon.size']},
+  );
+
+  @override
+  IconThemeData? get actionsIconTheme => IconThemeData(
+    color: ${componentColor('md.comp.top-app-bar.small.trailing-icon')},
+    size: ${tokens['md.comp.top-app-bar.small.trailing-icon.size']},
+  );
+
+  @override
+  TextStyle? get toolbarTextStyle => _textTheme.bodyText2;
+
+  @override
+  TextStyle? get titleTextStyle => ${textStyle('md.comp.top-app-bar.small.headline')};
+}''';
+}