DefaultTextStyle.merge and IconTheme.merge improvements (#9358)

I can't figure out if this is genius or a giant hack.

This lets you use DefaultTextStyle.merge and IconTheme.merge without
specifying a BuildContext. It automatically merges in at the
appropriate place in the tree using a Builder widget.

dev/manual_tests/card_collection.dart

@@ -248,8 +248,7 @@ class CardCollectionState extends State<CardCollection> {
                 controller: cardModel.textController,
               ),
             )
-          : new DefaultTextStyle.merge(
-              context: context,
+          : DefaultTextStyle.merge(
               style: cardLabelStyle.copyWith(
                 fontSize: _varyFontSizes ? 5.0 + index : null
               ),

packages/flutter/lib/src/material/app_bar.dart

@@ -438,8 +438,7 @@ class _AppBarState extends State<AppBar> {
     Widget appBar = new ClipRect(
       child: new CustomSingleChildLayout(
         delegate: const _ToolbarContainerLayout(),
-        child: new IconTheme.merge(
-          context: context,
+        child: IconTheme.merge(
           data: appBarIconTheme,
           child: new DefaultTextStyle(
             style: sideStyle,

packages/flutter/lib/src/material/bottom_navigation_bar.dart

@@ -347,8 +347,7 @@ class _BottomNavigationBarState extends State<BottomNavigationBar> with TickerPr
                       alignment: FractionalOffset.bottomCenter,
                       child: new Container(
                         margin: const EdgeInsets.only(bottom: 10.0),
-                        child: new DefaultTextStyle.merge(
-                          context: context,
+                        child: DefaultTextStyle.merge(
                           style: new TextStyle(
                             fontSize: 14.0,
                             color: colorTween.evaluate(_animations[i]),
@@ -419,8 +418,7 @@ class _BottomNavigationBarState extends State<BottomNavigationBar> with TickerPr
                         margin: const EdgeInsets.only(bottom: 10.0),
                         child: new FadeTransition(
                           opacity: _animations[i],
-                          child: new DefaultTextStyle.merge(
-                            context: context,
+                          child: DefaultTextStyle.merge(
                             style: const TextStyle(
                               fontSize: 14.0,
                               color: Colors.white

packages/flutter/lib/src/material/button.dart

@@ -292,8 +292,7 @@ class _MaterialButtonState extends State<MaterialButton> {
     final double height = widget.height ?? buttonTheme.height;
     final int elevation = (_highlight ? widget.highlightElevation : widget.elevation) ?? 0;
     final bool hasColorOrElevation = (widget.color != null || elevation > 0);
-    Widget contents = new IconTheme.merge(
-      context: context,
+    Widget contents = IconTheme.merge(
       data: new IconThemeData(
         color: textColor
       ),

packages/flutter/lib/src/material/data_table.dart

@@ -466,8 +466,7 @@ class DataTable extends StatelessWidget {
             ? (placeholder ? Colors.black38 : Colors.black87)
             : (placeholder ? Colors.white30 : Colors.white70)
         ),
-        child: new IconTheme.merge(
-          context: context,
+        child: IconTheme.merge(
           data: new IconThemeData(
             color: isLightTheme ? Colors.black54 : Colors.white70
           ),

packages/flutter/lib/src/material/floating_action_button.dart

@@ -124,8 +124,7 @@ class _FloatingActionButtonState extends State<FloatingActionButton> {
     }
 
     Widget result = new Center(
-      child: new IconTheme.merge(
-        context: context,
+      child: IconTheme.merge(
         data: new IconThemeData(color: iconColor),
         child: widget.child
       )

packages/flutter/lib/src/material/grid_tile_bar.dart

@@ -124,8 +124,7 @@ class GridTileBar extends StatelessWidget {
       height: (title != null && subtitle != null) ? 68.0 : 48.0,
       child: new Theme(
         data: darkTheme,
-        child: new IconTheme.merge(
-          context: context,
+        child: IconTheme.merge(
           data: const IconThemeData(color: Colors.white),
           child: new Row(
             crossAxisAlignment: CrossAxisAlignment.center,

packages/flutter/lib/src/material/icon_button.dart

@@ -151,8 +151,7 @@ class IconButton extends StatelessWidget {
           width: iconSize,
           child: new Align(
             alignment: alignment,
-            child: new IconTheme.merge(
-              context: context,
+            child: IconTheme.merge(
               data: new IconThemeData(
                 size: iconSize,
                 color: currentColor

packages/flutter/lib/src/material/icon_theme.dart

@@ -28,17 +28,20 @@ class IconTheme extends InheritedWidget {
   /// Creates an icon theme that controls the color, opacity, and size of
   /// descendant widgets, and merges in the current icon theme, if any.
   ///
-  /// The [context], [data], and [child] arguments must not be null.
-  factory IconTheme.merge({
+  /// The [data] and [child] arguments must not be null.
+  static Widget merge({
     Key key,
-    @required BuildContext context,
     @required IconThemeData data,
     @required Widget child
   }) {
-    return new IconTheme(
-      key: key,
-      data: _getInheritedIconThemeData(context).merge(data),
-      child: child
+    return new Builder(
+      builder: (BuildContext context) {
+        return new IconTheme(
+          key: key,
+          data: _getInheritedIconThemeData(context).merge(data),
+          child: child,
+        );
+      },
     );
   }
 

packages/flutter/lib/src/material/input_decorator.dart

@@ -439,8 +439,7 @@ class InputDecorator extends StatelessWidget {
           new Container(
             margin: new EdgeInsets.only(top: iconTop),
             width: isDense ? 40.0 : 48.0,
-            child: new IconTheme.merge(
-              context: context,
+            child: IconTheme.merge(
               data: new IconThemeData(
                 color: isFocused ? activeColor : Colors.black45,
                 size: isDense ? 18.0 : 24.0,

packages/flutter/lib/src/material/list_tile.dart

@@ -345,8 +345,7 @@ class ListTile extends StatelessWidget {
     final List<Widget> children = <Widget>[];
 
     if (leading != null) {
-      children.add(new IconTheme.merge(
-        context: context,
+      children.add(IconTheme.merge(
         data: new IconThemeData(color: _iconColor(theme, tileTheme)),
         child: new Container(
           margin: const EdgeInsets.only(right: 16.0),

packages/flutter/lib/src/material/paginated_data_table.dart

@@ -377,8 +377,7 @@ class PaginatedDataTableState extends State<PaginatedDataTable> {
             // See https://material.google.com/components/data-tables.html#data-tables-tables-within-cards
             style: _selectedRowCount > 0 ? themeData.textTheme.subhead.copyWith(color: themeData.accentColor)
                                          : themeData.textTheme.title.copyWith(fontWeight: FontWeight.w400),
-            child: new IconTheme.merge(
-              context: context,
+            child: IconTheme.merge(
               data: const IconThemeData(
                 opacity: 0.54
               ),
@@ -413,8 +412,7 @@ class PaginatedDataTableState extends State<PaginatedDataTable> {
           ),
           new DefaultTextStyle(
             style: footerTextStyle,
-            child: new IconTheme.merge(
-              context: context,
+            child: IconTheme.merge(
               data: const IconThemeData(
                 opacity: 0.54
               ),

packages/flutter/lib/src/material/popup_menu.dart

@@ -160,8 +160,7 @@ class _PopupMenuItemState<T extends PopupMenuItem<dynamic>> extends State<T> {
     );
     if (!widget.enabled) {
       final bool isDark = theme.brightness == Brightness.dark;
-      item = new IconTheme.merge(
-        context: context,
+      item = IconTheme.merge(
         data: new IconThemeData(opacity: isDark ? 0.5 : 0.38),
         child: item
       );

packages/flutter/lib/src/material/tabs.dart

@@ -138,8 +138,7 @@ class _TabStyle extends AnimatedWidget {
 
     return new DefaultTextStyle(
       style: textStyle.copyWith(color: color),
-      child: new IconTheme.merge(
-        context: context,
+      child: IconTheme.merge(
         data: new IconThemeData(
           size: 24.0,
           color: color,

packages/flutter/lib/src/material/two_level_list.dart

@@ -201,8 +201,7 @@ class _TwoLevelSublistState extends State<TwoLevelSublist> with SingleTickerProv
       ),
       child: new Column(
         children: <Widget>[
-          new IconTheme.merge(
-            context: context,
+          IconTheme.merge(
             data: new IconThemeData(color: _iconColor.evaluate(_easeInAnimation)),
             child: new TwoLevelListItem(
               onTap: _handleOnTap,

packages/flutter/lib/src/widgets/text.dart

@@ -41,15 +41,15 @@ class DefaultTextStyle extends InheritedWidget {
       maxLines = null,
       overflow = TextOverflow.clip;
 
-  /// Creates a default text style that inherits from the given [BuildContext].
+  /// Creates a default text style that overrides the text styles in scope at
+  /// this point in the widget tree.
   ///
   /// The given [style] is merged with the [style] from the default text style
-  /// for the given [BuildContext] and, if non-null, the given [textAlign]
-  /// replaces the [textAlign] from the default text style for the given
-  /// [BuildContext].
-  factory DefaultTextStyle.merge({
+  /// for the [BuildContext] where the widget is inserted, and any of the other
+  /// arguments that are not null replace the corresponding properties on that
+  /// same default text style.
+  static Widget merge({
     Key key,
-    @required BuildContext context,
     TextStyle style,
     TextAlign textAlign,
     bool softWrap,
@@ -57,17 +57,20 @@ class DefaultTextStyle extends InheritedWidget {
     int maxLines,
     @required Widget child,
   }) {
-    assert(context != null);
     assert(child != null);
-    final DefaultTextStyle parent = DefaultTextStyle.of(context);
-    return new DefaultTextStyle(
-      key: key,
-      style: parent.style.merge(style),
-      textAlign: textAlign ?? parent.textAlign,
-      softWrap: softWrap ?? parent.softWrap,
-      overflow: overflow ?? parent.overflow,
-      maxLines: maxLines ?? parent.maxLines,
-      child: child
+    return new Builder(
+      builder: (BuildContext context) {
+        final DefaultTextStyle parent = DefaultTextStyle.of(context);
+        return new DefaultTextStyle(
+          key: key,
+          style: parent.style.merge(style),
+          textAlign: textAlign ?? parent.textAlign,
+          softWrap: softWrap ?? parent.softWrap,
+          overflow: overflow ?? parent.overflow,
+          maxLines: maxLines ?? parent.maxLines,
+          child: child
+        );
+      },
     );
   }
 

packages/flutter/test/material/popup_menu_test.dart

@@ -7,6 +7,7 @@ import 'package:flutter/material.dart';
 
 void main() {
   testWidgets('Navigator.push works within a PopupMenuButton', (WidgetTester tester) async {
+    final Key targetKey = new UniqueKey();
     await tester.pumpWidget(
       new MaterialApp(
         routes: <String, WidgetBuilder> {
@@ -17,6 +18,7 @@ void main() {
         home: new Material(
           child: new Center(
             child: new Builder(
+              key: targetKey,
               builder: (BuildContext context) {
                 return new PopupMenuButton<int>(
                   onSelected: (int value) {
@@ -38,7 +40,7 @@ void main() {
       )
     );
 
-    await tester.tap(find.byType(Builder));
+    await tester.tap(find.byKey(targetKey));
     await tester.pump();
     await tester.pump(const Duration(seconds: 1)); // finish the menu animation