Appbar iconTheme override fix (#118681)

* theme override fix

* add conditional centering

Author: Eilidh Southren

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

@@ -1023,39 +1023,35 @@ class _AppBarState extends State<AppBar> {
     }
     if (leading != null) {
       if (theme.useMaterial3) {
-        if (leading is IconButton) {
-          final IconButtonThemeData effectiveIconButtonTheme;
-
-          // This comparison is to check if there is a custom [overallIconTheme]. If true, it means that no
-          // custom [overallIconTheme] is provided, so [iconButtonTheme] is applied. Otherwise, we generate
-          // a new [IconButtonThemeData] based on the values from [overallIconTheme]. If [iconButtonTheme] only
-          // has null values, the default [overallIconTheme] will be applied below by [IconTheme.merge]
-          if (overallIconTheme == defaults.iconTheme) {
-            effectiveIconButtonTheme = iconButtonTheme;
-          } else {
-            // The [IconButton.styleFrom] method is used to generate a correct [overlayColor] based on the [foregroundColor].
-            final ButtonStyle leadingIconButtonStyle = IconButton.styleFrom(
-              foregroundColor: overallIconTheme.color,
-              iconSize: overallIconTheme.size,
-            );
-
-            effectiveIconButtonTheme = IconButtonThemeData(
-              style: iconButtonTheme.style?.copyWith(
-                foregroundColor: leadingIconButtonStyle.foregroundColor,
-                overlayColor: leadingIconButtonStyle.overlayColor,
-                iconSize: leadingIconButtonStyle.iconSize,
-              )
-            );
-          }
-
-          leading = Center(
-            child: IconButtonTheme(
-              data: effectiveIconButtonTheme,
-              child: leading
+        final IconButtonThemeData effectiveIconButtonTheme;
+
+        // This comparison is to check if there is a custom [overallIconTheme]. If true, it means that no
+        // custom [overallIconTheme] is provided, so [iconButtonTheme] is applied. Otherwise, we generate
+        // a new [IconButtonThemeData] based on the values from [overallIconTheme]. If [iconButtonTheme] only
+        // has null values, the default [overallIconTheme] will be applied below by [IconTheme.merge]
+        if (overallIconTheme == defaults.iconTheme) {
+          effectiveIconButtonTheme = iconButtonTheme;
+        } else {
+          // The [IconButton.styleFrom] method is used to generate a correct [overlayColor] based on the [foregroundColor].
+          final ButtonStyle leadingIconButtonStyle = IconButton.styleFrom(
+            foregroundColor: overallIconTheme.color,
+            iconSize: overallIconTheme.size,
+          );
+
+          effectiveIconButtonTheme = IconButtonThemeData(
+            style: iconButtonTheme.style?.copyWith(
+              foregroundColor: leadingIconButtonStyle.foregroundColor,
+              overlayColor: leadingIconButtonStyle.overlayColor,
+              iconSize: leadingIconButtonStyle.iconSize,
             )
           );
         }
 
+        leading = IconButtonTheme(
+            data: effectiveIconButtonTheme,
+            child: leading is IconButton ? Center(child: leading) : leading,
+        );
+
         // Based on the Material Design 3 specs, the leading IconButton should have
         // a size of 48x48, and a highlight size of 40x40. Users can also put other
         // type of widgets on leading with the original config.

packages/flutter/test/material/app_bar_test.dart

@@ -3235,6 +3235,39 @@ void main() {
       expect(actionIconButtonSize(), 30.0);
     });
 
+    testWidgets('AppBar.iconTheme should override any IconButtonTheme present in the theme for widgets containing an iconButton - M3', (WidgetTester tester) async {
+      final ThemeData themeData = ThemeData(
+        iconButtonTheme: IconButtonThemeData(
+          style: IconButton.styleFrom(
+            foregroundColor: Colors.red,
+            iconSize: 32.0,
+          ),
+        ),
+        useMaterial3: true,
+      );
+
+      const IconThemeData overallIconTheme = IconThemeData(color: Colors.yellow, size: 30.0);
+      await tester.pumpWidget(
+        MaterialApp(
+          theme: themeData,
+          home: Scaffold(
+            appBar: AppBar(
+              iconTheme: overallIconTheme,
+              leading: BackButton(onPressed: () {}),
+              title: const Text('title'),
+            ),
+          ),
+        ),
+      );
+
+      Color? leadingIconButtonColor() => iconStyle(tester, Icons.arrow_back)?.color;
+      double? leadingIconButtonSize() => iconStyle(tester, Icons.arrow_back)?.fontSize;
+
+      expect(leadingIconButtonColor(), Colors.yellow);
+      expect(leadingIconButtonSize(), 30.0);
+
+    });
+
     testWidgets('AppBar.actionsIconTheme should override any IconButtonTheme present in the theme - M3', (WidgetTester tester) async {
       final ThemeData themeData = ThemeData(
         iconButtonTheme: IconButtonThemeData(
@@ -3275,6 +3308,40 @@ void main() {
       expect(actionIconButtonSize(), 30.0);
     });
 
+    testWidgets('AppBar.actionsIconTheme should override any IconButtonTheme present in the theme for widgets containing an iconButton - M3', (WidgetTester tester) async {
+      final ThemeData themeData = ThemeData(
+        iconButtonTheme: IconButtonThemeData(
+          style: IconButton.styleFrom(
+            foregroundColor: Colors.red,
+            iconSize: 32.0,
+          ),
+        ),
+        useMaterial3: true,
+      );
+
+      const IconThemeData actionsIconTheme = IconThemeData(color: Colors.yellow, size: 30.0);
+      await tester.pumpWidget(
+        MaterialApp(
+          theme: themeData,
+          home: Scaffold(
+            appBar: AppBar(
+              actionsIconTheme: actionsIconTheme,
+              title: const Text('title'),
+              actions: <Widget>[
+                BackButton(onPressed: () {}),
+              ],
+            ),
+          ),
+        ),
+      );
+
+      Color? actionIconButtonColor() => iconStyle(tester, Icons.arrow_back)?.color;
+      double? actionIconButtonSize() => iconStyle(tester, Icons.arrow_back)?.fontSize;
+
+      expect(actionIconButtonColor(), Colors.yellow);
+      expect(actionIconButtonSize(), 30.0);
+    });
+
     testWidgets('The foregroundColor property of the AppBar overrides any IconButtonTheme present in the theme - M3', (WidgetTester tester) async {
       final ThemeData themeData = ThemeData(
         iconButtonTheme: IconButtonThemeData(