Fix actions padding for M3 alert dialogs (#105008)

* update docs

* use correct actions padding for dialogs

* remove trailing spaces

* Update dialog_theme.dart

* Update packages/flutter/lib/src/material/dialog.dart
Co-authored-by: Taha Tesser <tessertaha@gmail.com>
Co-authored-by: Taha Tesser <tessertaha@gmail.com>

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

@@ -268,7 +268,7 @@ class AlertDialog extends StatelessWidget {
     this.contentPadding = const EdgeInsets.fromLTRB(24.0, 20.0, 24.0, 24.0),
     this.contentTextStyle,
     this.actions,
-    this.actionsPadding = EdgeInsets.zero,
+    this.actionsPadding,
     this.actionsAlignment,
     this.actionsOverflowAlignment,
     this.actionsOverflowDirection,
@@ -350,10 +350,9 @@ class AlertDialog extends StatelessWidget {
   /// Typically used to provide padding to the button bar between the button bar
   /// and the edges of the dialog.
   ///
-  /// If are no [actions], then no padding will be included. The padding around
-  /// the button bar defaults to zero. It is also important to note that
-  /// [buttonPadding] may contribute to the padding on the edges of [actions] as
-  /// well.
+  /// If there are no [actions], then no padding will be included. It is also
+  /// important to note that [buttonPadding] may contribute to the padding on
+  /// the edges of [actions] as well.
   ///
   /// {@tool snippet}
   /// This is an example of a set of actions aligned with the content widget.
@@ -373,7 +372,7 @@ class AlertDialog extends StatelessWidget {
   /// See also:
   ///
   /// * [OverflowBar], which [actions] configures to lay itself out.
-  final EdgeInsetsGeometry actionsPadding;
+  final EdgeInsetsGeometry? actionsPadding;
 
   /// Defines the horizontal layout of the [actions] according to the same
   /// rules as for [Row.mainAxisAlignment].
@@ -507,8 +506,6 @@ class AlertDialog extends StatelessWidget {
     // children.
     final double paddingScaleFactor = _paddingScaleFactor(MediaQuery.of(context).textScaleFactor);
     final TextDirection? textDirection = Directionality.maybeOf(context);
-    const double m3ActionEndPadding = 18.0;
-    const double m3ActionBottomPadding = 12.0;
 
     Widget? titleWidget;
     Widget? contentWidget;
@@ -557,14 +554,11 @@ class AlertDialog extends StatelessWidget {
 
     if (actions != null) {
       final double spacing = (buttonPadding?.horizontal ?? 16) / 2;
+      final EdgeInsetsGeometry effetiveActionsPadding = (actionsPadding ?? EdgeInsets.zero).add(
+        theme.useMaterial3 ? const EdgeInsets.only(left: 24.0, right: 24.0, bottom: 24.0) : EdgeInsets.all(spacing),
+      );
       actionsWidget = Padding(
-        padding: theme.useMaterial3
-          ? actionsPadding.add(EdgeInsets.all(spacing))
-            .add(const EdgeInsets.only(
-              right: m3ActionEndPadding,
-              bottom: m3ActionBottomPadding,
-            ))
-          : actionsPadding.add(EdgeInsets.all(spacing)),
+        padding: effetiveActionsPadding,
         child: OverflowBar(
           alignment: actionsAlignment ?? MainAxisAlignment.end,
           spacing: spacing,

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

@@ -15,16 +15,13 @@ import 'theme.dart';
 /// `DialogTheme.of(context)`. Instances of [DialogTheme] can be customized with
 /// [DialogTheme.copyWith].
 ///
-/// When Shape is `null`, the dialog defaults to a [RoundedRectangleBorder] with
-/// a border radius of 2.0 on all corners.
-///
-/// [titleTextStyle] and [contentTextStyle] are used in [AlertDialog]s.
-/// If null, they default to [TextTheme.headline6] and [TextTheme.subtitle1],
-/// respectively.
+/// [titleTextStyle] and [contentTextStyle] are used in [AlertDialog]s and [SimpleDialog]s.
 ///
 /// See also:
 ///
-///  * [Dialog], a Material Design dialog that can be customized using this [DialogTheme].
+///  * [Dialog], a dialog that can be customized using this [DialogTheme].
+///  * [AlertDialog], a dialog that can be customized using this [DialogTheme].
+///  * [SimpleDialog], a dialog that can be customized using this [DialogTheme].
 ///  * [ThemeData], which describes the overall theme information for the
 ///    application.
 @immutable
@@ -39,33 +36,24 @@ class DialogTheme with Diagnosticable {
     this.contentTextStyle,
   });
 
-  /// Default value for [Dialog.backgroundColor].
-  ///
-  /// If null, [ThemeData.dialogBackgroundColor] is used, if that's null,
-  /// defaults to [Colors.white].
+  /// Overrides the default value for [Dialog.backgroundColor].
   final Color? backgroundColor;
 
-  /// Default value for [Dialog.elevation].
-  ///
-  /// If null, the [Dialog] elevation defaults to `24.0`.
+  /// Overrides the default value for [Dialog.elevation].
   final double? elevation;
 
-  /// Default value for [Dialog.shape].
+  /// Overrides the default value for [Dialog.shape].
   final ShapeBorder? shape;
 
-  /// Default value for [Dialog.alignment].
-  ///
-  /// If null, the [Dialog] alignment defaults to [Alignment.center].
+  /// Overrides the default value for [Dialog.alignment].
   final AlignmentGeometry? alignment;
 
-  /// Used to configure the [DefaultTextStyle] for the [AlertDialog.title] widget.
-  ///
-  /// If null, defaults to [TextTheme.headline6] of [ThemeData.textTheme].
+  /// Overrides the default value for [DefaultTextStyle] for [SimpleDialog.title] and
+  /// [AlertDialog.title].
   final TextStyle? titleTextStyle;
 
-  /// Used to configure the [DefaultTextStyle] for the [AlertDialog.content] widget.
-  ///
-  /// If null, defaults to [TextTheme.subtitle1] of [ThemeData.textTheme].
+  /// Overrides the default value for [DefaultTextStyle] for [SimpleDialog.children] and
+  /// [AlertDialog.content].
   final TextStyle? contentTextStyle;
 
   /// Creates a copy of this object but with the given fields replaced with the

packages/flutter/test/material/dialog_test.dart

@@ -658,25 +658,25 @@ void main() {
     // First button
     expect(
       tester.getTopRight(find.byKey(key1)).dy,
-      tester.getTopRight(_findButtonBar()).dy + 8.0,
+      tester.getTopRight(_findButtonBar()).dy,
     ); // top
     expect(
       tester.getBottomRight(find.byKey(key1)).dy,
-      tester.getBottomRight(_findButtonBar()).dy - 20.0,
+      tester.getBottomRight(_findButtonBar()).dy - 24.0,
     ); // bottom
 
     // // Second button
     expect(
       tester.getTopRight(find.byKey(key2)).dy,
-      tester.getTopRight(_findButtonBar()).dy + 8.0,
+      tester.getTopRight(_findButtonBar()).dy,
     ); // top
     expect(
       tester.getBottomRight(find.byKey(key2)).dy,
-      tester.getBottomRight(_findButtonBar()).dy - 20.0,
+      tester.getBottomRight(_findButtonBar()).dy - 24.0,
     ); // bottom
     expect(
       tester.getBottomRight(find.byKey(key2)).dx,
-      tester.getBottomRight(_findButtonBar()).dx - 26.0,
+      tester.getBottomRight(_findButtonBar()).dx - 24.0,
     ); // right
   });