Add a way to customize padding in BottomAppBar (#115175)

* squash 5 into 1

fix

Update packages/flutter/lib/src/material/bottom_app_bar.dart

lint

update tests
Co-Authored-By: Hans Muller <hansmuller@chromium.org>

* lint
Co-authored-by: Hans Muller <hansmuller@chromium.org>

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

@@ -69,6 +69,7 @@ class BottomAppBar extends StatefulWidget {
     this.clipBehavior = Clip.none,
     this.notchMargin = 4.0,
     this.child,
+    this.padding,
     this.surfaceTintColor,
     this.height,
   }) : assert(elevation == null || elevation >= 0.0),
@@ -83,6 +84,12 @@ class BottomAppBar extends StatefulWidget {
   /// being an [IconButton] with the [Icons.menu] icon.
   final Widget? child;
 
+  /// The amount of space to surround the child inside the bounds of the [BottomAppBar].
+  ///
+  /// In Material 3 the padding will default to `EdgeInsets.symmetric(vertical: 12.0, horizontal: 16.0)`
+  /// Otherwise the value will default to EdgeInsets.zero.
+  final EdgeInsetsGeometry? padding;
+
   /// The bottom app bar's background color.
   ///
   /// If this property is null then [BottomAppBarTheme.color] of
@@ -173,10 +180,10 @@ class _BottomAppBarState extends State<BottomAppBar> {
     final Color surfaceTintColor = widget.surfaceTintColor ?? babTheme.surfaceTintColor ?? defaults.surfaceTintColor!;
     final Color effectiveColor = isMaterial3 ? color : ElevationOverlay.applyOverlay(context, color, elevation);
 
-    final Widget? child = isMaterial3 ? Padding(
-      padding: const EdgeInsets.symmetric(vertical: 12.0, horizontal: 16.0),
+    final Widget child = Padding(
+      padding: widget.padding ?? babTheme.padding ?? (isMaterial3 ? const EdgeInsets.symmetric(vertical: 12.0, horizontal: 16.0) : EdgeInsets.zero),
       child: widget.child,
-    ) : widget.child;
+    );
 
     return SizedBox(
       height: height,

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

@@ -34,31 +34,35 @@ class BottomAppBarTheme with Diagnosticable {
     this.shape,
     this.height,
     this.surfaceTintColor,
+    this.padding,
   });
 
-  /// Default value for [BottomAppBar.color].
+  /// Overrides the default value for [BottomAppBar.color].
   ///
   /// If null, [BottomAppBar] uses [ThemeData.bottomAppBarColor].
   final Color? color;
 
-  /// Default value for [BottomAppBar.elevation].
+  /// Overrides the default value for [BottomAppBar.elevation].
   final double? elevation;
 
-  /// Default value for [BottomAppBar.shape].
+  /// Overrides the default value for [BottomAppBar.shape].
   final NotchedShape? shape;
 
-  /// Default value for [BottomAppBar.height].
+  /// Overrides the default value for [BottomAppBar.height].
   ///
   /// If null, [BottomAppBar] height will be the minimum on the non material 3.
   final double? height;
 
-  /// Default value for [BottomAppBar.surfaceTintColor].
+  /// Overrides the default value for [BottomAppBar.surfaceTintColor].
   ///
   /// If null, [BottomAppBar] will not display an overlay color.
   ///
   /// See [Material.surfaceTintColor] for more details.
   final Color? surfaceTintColor;
 
+  /// Overrides the default value for [BottomAppBar.padding].
+  final EdgeInsetsGeometry? padding;
+
   /// Creates a copy of this object but with the given fields replaced with the
   /// new values.
   BottomAppBarTheme copyWith({
@@ -67,6 +71,7 @@ class BottomAppBarTheme with Diagnosticable {
     NotchedShape? shape,
     double? height,
     Color? surfaceTintColor,
+    EdgeInsetsGeometry? padding,
   }) {
     return BottomAppBarTheme(
       color: color ?? this.color,
@@ -74,6 +79,7 @@ class BottomAppBarTheme with Diagnosticable {
       shape: shape ?? this.shape,
       height: height ?? this.height,
       surfaceTintColor: surfaceTintColor ?? this.surfaceTintColor,
+      padding: padding ?? this.padding,
     );
   }
 
@@ -94,7 +100,8 @@ class BottomAppBarTheme with Diagnosticable {
       elevation: lerpDouble(a?.elevation, b?.elevation, t),
       shape: t < 0.5 ? a?.shape : b?.shape,
       height: lerpDouble(a?.height, b?.height, t),
-      surfaceTintColor: Color.lerp(a?.color, b?.color, t),
+      surfaceTintColor: Color.lerp(a?.surfaceTintColor, b?.surfaceTintColor, t),
+      padding: EdgeInsetsGeometry.lerp(a?.padding, b?.padding, t),
     );
   }
 
@@ -105,6 +112,7 @@ class BottomAppBarTheme with Diagnosticable {
     shape,
     height,
     surfaceTintColor,
+    padding,
   );
 
   @override
@@ -120,7 +128,8 @@ class BottomAppBarTheme with Diagnosticable {
         && other.elevation == elevation
         && other.shape == shape
         && other.height == height
-        && other.surfaceTintColor == surfaceTintColor;
+        && other.surfaceTintColor == surfaceTintColor
+        && other.padding == padding;
   }
 
   @override
@@ -131,5 +140,6 @@ class BottomAppBarTheme with Diagnosticable {
     properties.add(DiagnosticsProperty<NotchedShape>('shape', shape, defaultValue: null));
     properties.add(DiagnosticsProperty<double>('height', height, defaultValue: null));
     properties.add(ColorProperty('surfaceTintColor', surfaceTintColor, defaultValue: null));
+    properties.add(DiagnosticsProperty<EdgeInsetsGeometry>('padding', padding, defaultValue: null));
   }
 }

packages/flutter/test/material/bottom_app_bar_test.dart

@@ -85,6 +85,71 @@ void main() {
     );
   }, skip: isBrowser); // https://github.com/flutter/flutter/issues/44572
 
+
+  testWidgets('Custom Padding', (WidgetTester tester) async {
+  const EdgeInsets customPadding = EdgeInsets.all(10);
+    await tester.pumpWidget(
+      MaterialApp(
+        theme: ThemeData.from(colorScheme: const ColorScheme.light()),
+        home: Builder(
+          builder: (BuildContext context) {
+            return const Scaffold(
+              body: Align(
+                alignment: Alignment.bottomCenter,
+                child: BottomAppBar(
+                  padding: customPadding,
+                    child:ColoredBox(
+                      color:Colors.green,
+                      child:SizedBox(width: 300, height: 60),
+                    ),
+                ),
+              ),
+            );
+          },
+        ),
+      ),
+    );
+
+    final BottomAppBar bottomAppBar = tester.widget(find.byType(BottomAppBar));
+    expect(bottomAppBar.padding, customPadding);
+    final  Rect babRect = tester.getRect(find.byType(BottomAppBar));
+    final  Rect childRect = tester.getRect(find.byType(ColoredBox));
+    expect(childRect, const Rect.fromLTRB(250, 530, 550, 590));
+    expect(babRect, const Rect.fromLTRB(240, 520, 560, 600));
+  });
+
+  testWidgets('Custom Padding in Material 3', (WidgetTester tester) async {
+  const EdgeInsets customPadding = EdgeInsets.all(10);
+    await tester.pumpWidget(
+      MaterialApp(
+        theme: ThemeData.from(colorScheme: const ColorScheme.light(), useMaterial3: true),
+        home: Builder(
+          builder: (BuildContext context) {
+            return const Scaffold(
+              body: Align(
+                alignment: Alignment.bottomCenter,
+                child: BottomAppBar(
+                  padding: customPadding,
+                    child:ColoredBox(
+                      color:Colors.green,
+                      child:SizedBox(width: 300, height: 60),
+                    ),
+                ),
+              ),
+            );
+          },
+        ),
+      ),
+    );
+
+    final BottomAppBar bottomAppBar = tester.widget(find.byType(BottomAppBar));
+    expect(bottomAppBar.padding, customPadding);
+    final  Rect babRect = tester.getRect(find.byType(BottomAppBar));
+    final  Rect childRect = tester.getRect(find.byType(ColoredBox));
+    expect(childRect, const Rect.fromLTRB(250, 530, 550, 590));
+    expect(babRect, const Rect.fromLTRB(240, 520, 560, 600));
+  });
+
   testWidgets('color defaults to Theme.bottomAppBarColor', (WidgetTester tester) async {
     await tester.pumpWidget(
       MaterialApp(