Reland Alert dialog overflow spacing (#50675)

* Add ButtonBar.overflowButtonSpacing

* Add AlertDialog overflow button spacing functionality

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

@@ -65,9 +65,11 @@ class ButtonBar extends StatelessWidget {
     this.buttonAlignedDropdown,
     this.layoutBehavior,
     this.overflowDirection,
+    this.overflowButtonSpacing,
     this.children = const <Widget>[],
   }) : assert(buttonMinWidth == null || buttonMinWidth >= 0.0),
        assert(buttonHeight == null || buttonHeight >= 0.0),
+       assert(overflowButtonSpacing == null || overflowButtonSpacing >= 0.0),
        super(key: key);
 
   /// How the children should be placed along the horizontal axis.
@@ -143,6 +145,22 @@ class ButtonBar extends StatelessWidget {
   /// default to [VerticalDirection.down].
   final VerticalDirection overflowDirection;
 
+  /// The spacing between buttons when the button bar overflows.
+  ///
+  /// If the [children] do not fit into a single row, they are
+  /// arranged into a column. This parameter provides additional
+  /// vertical space in between buttons when it does overflow.
+  ///
+  /// Note that the button spacing may appear to be more than
+  /// the value provided. This is because most buttons adhere to the
+  /// [MaterialTapTargetSize] of 48px. So, even though a button
+  /// might visually be 36px in height, it might still take up to
+  /// 48px vertically.
+  ///
+  /// If null then no spacing will be added in between buttons in
+  /// an overflow state.
+  final double overflowButtonSpacing;
+
   /// The buttons to arrange horizontally.
   ///
   /// Typically [RaisedButton] or [FlatButton] widgets.
@@ -176,6 +194,7 @@ class ButtonBar extends StatelessWidget {
             child: child,
           );
         }).toList(),
+        overflowButtonSpacing: overflowButtonSpacing,
       ),
     );
     switch (buttonTheme.layoutBehavior) {
@@ -226,6 +245,7 @@ class _ButtonBarRow extends Flex {
     TextDirection textDirection,
     VerticalDirection overflowDirection = VerticalDirection.down,
     TextBaseline textBaseline,
+    this.overflowButtonSpacing,
   }) : super(
     children: children,
     direction: direction,
@@ -237,6 +257,8 @@ class _ButtonBarRow extends Flex {
     textBaseline: textBaseline,
   );
 
+  final double overflowButtonSpacing;
+
   @override
   _RenderButtonBarRow createRenderObject(BuildContext context) {
     return _RenderButtonBarRow(
@@ -247,6 +269,7 @@ class _ButtonBarRow extends Flex {
       textDirection: getEffectiveTextDirection(context),
       verticalDirection: verticalDirection,
       textBaseline: textBaseline,
+      overflowButtonSpacing: overflowButtonSpacing,
     );
   }
 
@@ -259,7 +282,8 @@ class _ButtonBarRow extends Flex {
       ..crossAxisAlignment = crossAxisAlignment
       ..textDirection = getEffectiveTextDirection(context)
       ..verticalDirection = verticalDirection
-      ..textBaseline = textBaseline;
+      ..textBaseline = textBaseline
+      ..overflowButtonSpacing = overflowButtonSpacing;
   }
 }
 
@@ -289,7 +313,9 @@ class _RenderButtonBarRow extends RenderFlex {
     @required TextDirection textDirection,
     VerticalDirection verticalDirection = VerticalDirection.down,
     TextBaseline textBaseline,
+    this.overflowButtonSpacing,
   }) : assert(textDirection != null),
+       assert(overflowButtonSpacing == null || overflowButtonSpacing >= 0),
        super(
          children: children,
          direction: direction,
@@ -302,6 +328,7 @@ class _RenderButtonBarRow extends RenderFlex {
        );
 
   bool _hasCheckedLayoutWidth = false;
+  double overflowButtonSpacing;
 
   @override
   BoxConstraints get constraints {
@@ -391,6 +418,9 @@ class _RenderButtonBarRow extends RenderFlex {
             child = childParentData.previousSibling;
             break;
         }
+
+        if (overflowButtonSpacing != null && child != null)
+          currentHeight += overflowButtonSpacing;
       }
       size = constraints.constrain(Size(constraints.maxWidth, currentHeight));
     }

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

@@ -20,6 +20,7 @@ import 'ink_well.dart';
 import 'material.dart';
 import 'material_localizations.dart';
 import 'theme.dart';
+import 'theme_data.dart';
 
 // Examples can assume:
 // enum Department { treasury, state }
@@ -223,6 +224,7 @@ class AlertDialog extends StatelessWidget {
     this.actions,
     this.actionsPadding = EdgeInsets.zero,
     this.actionsOverflowDirection,
+    this.actionsOverflowButtonSpacing,
     this.buttonPadding,
     this.backgroundColor,
     this.elevation,
@@ -342,6 +344,22 @@ class AlertDialog extends StatelessWidget {
   /// * [ButtonBar], which [actions] configures to lay itself out.
   final VerticalDirection actionsOverflowDirection;
 
+  /// The spacing between [actions] when the button bar overflows.
+  ///
+  /// If the widgets in [actions] do not fit into a single row, they are
+  /// arranged into a column. This parameter provides additional
+  /// vertical space in between buttons when it does overflow.
+  ///
+  /// Note that the button spacing may appear to be more than
+  /// the value provided. This is because most buttons adhere to the
+  /// [MaterialTapTargetSize] of 48px. So, even though a button
+  /// might visually be 36px in height, it might still take up to
+  /// 48px vertically.
+  ///
+  /// If null then no spacing will be added in between buttons in
+  /// an overflow state.
+  final double actionsOverflowButtonSpacing;
+
   /// The padding that surrounds each button in [actions].
   ///
   /// This is different from [actionsPadding], which defines the padding
@@ -445,6 +463,7 @@ class AlertDialog extends StatelessWidget {
         child: ButtonBar(
           buttonPadding: buttonPadding,
           overflowDirection: actionsOverflowDirection,
+          overflowButtonSpacing: actionsOverflowButtonSpacing,
           children: actions,
         ),
       );

packages/flutter/test/material/button_bar_test.dart

@@ -570,7 +570,60 @@ void main() {
         final Rect containerOneRect = tester.getRect(find.byKey(keyOne));
         final Rect containerTwoRect = tester.getRect(find.byKey(keyTwo));
         // Second [Container] should appear above first container.
-        expect(containerTwoRect.bottom, containerOneRect.top);
+        expect(containerTwoRect.bottom, lessThanOrEqualTo(containerOneRect.top));
+      },
+    );
+
+    testWidgets(
+      'ButtonBar has no spacing by default when overflowing',
+      (WidgetTester tester) async {
+        final Key keyOne = UniqueKey();
+        final Key keyTwo = UniqueKey();
+        await tester.pumpWidget(
+          MaterialApp(
+            home: ButtonBar(
+              alignment: MainAxisAlignment.center,
+              // Set padding to zero to align buttons with edge of button bar.
+              buttonPadding: EdgeInsets.zero,
+              children: <Widget>[
+                Container(key: keyOne, height: 50.0, width: 500.0),
+                Container(key: keyTwo, height: 50.0, width: 500.0),
+              ],
+            ),
+          ),
+        );
+
+        final Rect containerOneRect = tester.getRect(find.byKey(keyOne));
+        final Rect containerTwoRect = tester.getRect(find.byKey(keyTwo));
+        expect(containerOneRect.bottom, containerTwoRect.top);
+      },
+    );
+
+    testWidgets(
+      "ButtonBar's children respects overflowButtonSpacing when overflowing",
+      (WidgetTester tester) async {
+        final Key keyOne = UniqueKey();
+        final Key keyTwo = UniqueKey();
+        await tester.pumpWidget(
+          MaterialApp(
+            home: ButtonBar(
+              alignment: MainAxisAlignment.center,
+              // Set padding to zero to align buttons with edge of button bar.
+              buttonPadding: EdgeInsets.zero,
+              // Set the overflow button spacing to ensure add some space between
+              // buttons in an overflow case.
+              overflowButtonSpacing: 10.0,
+              children: <Widget>[
+                Container(key: keyOne, height: 50.0, width: 500.0),
+                Container(key: keyTwo, height: 50.0, width: 500.0),
+              ],
+            ),
+          ),
+        );
+
+        final Rect containerOneRect = tester.getRect(find.byKey(keyOne));
+        final Rect containerTwoRect = tester.getRect(find.byKey(keyTwo));
+        expect(containerOneRect.bottom, containerTwoRect.top - 10.0);
       },
     );
   });

packages/flutter/test/material/dialog_test.dart

@@ -557,7 +557,7 @@ void main() {
     ); // right
   });
 
-  testWidgets('Dialogs can set the vertical direction of actions', (WidgetTester tester) async {
+  testWidgets('Dialogs can set the vertical direction of overflowing actions', (WidgetTester tester) async {
     final GlobalKey key1 = GlobalKey();
     final GlobalKey key2 = GlobalKey();
 
@@ -589,7 +589,74 @@ void main() {
     final Rect buttonOneRect = tester.getRect(find.byKey(key1));
     final Rect buttonTwoRect = tester.getRect(find.byKey(key2));
     // Second [RaisedButton] should appear above the first.
-    expect(buttonTwoRect.bottom, buttonOneRect.top);
+    expect(buttonTwoRect.bottom, lessThanOrEqualTo(buttonOneRect.top));
+  });
+
+  testWidgets('Dialogs have no spacing by default for overflowing actions', (WidgetTester tester) async {
+    final GlobalKey key1 = GlobalKey();
+    final GlobalKey key2 = GlobalKey();
+
+    final AlertDialog dialog = AlertDialog(
+      title: const Text('title'),
+      content: const Text('content'),
+      actions: <Widget>[
+        RaisedButton(
+          key: key1,
+          onPressed: () {},
+          child: const Text('Looooooooooooooong button 1'),
+        ),
+        RaisedButton(
+          key: key2,
+          onPressed: () {},
+          child: const Text('Looooooooooooooong button 2'),
+        ),
+      ],
+    );
+
+    await tester.pumpWidget(
+      _buildAppWithDialog(dialog),
+    );
+
+    await tester.tap(find.text('X'));
+    await tester.pumpAndSettle();
+
+    final Rect buttonOneRect = tester.getRect(find.byKey(key1));
+    final Rect buttonTwoRect = tester.getRect(find.byKey(key2));
+    expect(buttonOneRect.bottom, buttonTwoRect.top);
+  });
+
+  testWidgets('Dialogs can set the button spacing of overflowing actions', (WidgetTester tester) async {
+    final GlobalKey key1 = GlobalKey();
+    final GlobalKey key2 = GlobalKey();
+
+    final AlertDialog dialog = AlertDialog(
+      title: const Text('title'),
+      content: const Text('content'),
+      actions: <Widget>[
+        RaisedButton(
+          key: key1,
+          onPressed: () {},
+          child: const Text('Looooooooooooooong button 1'),
+        ),
+        RaisedButton(
+          key: key2,
+          onPressed: () {},
+          child: const Text('Looooooooooooooong button 2'),
+        ),
+      ],
+      actionsOverflowButtonSpacing: 10.0,
+    );
+
+    await tester.pumpWidget(
+      _buildAppWithDialog(dialog),
+    );
+
+    await tester.tap(find.text('X'));
+    await tester.pumpAndSettle();
+
+    final Rect buttonOneRect = tester.getRect(find.byKey(key1));
+    final Rect buttonTwoRect = tester.getRect(find.byKey(key2));
+    expect(buttonOneRect.bottom, buttonTwoRect.top - 10.0);
   });
 
   testWidgets('Dialogs removes MediaQuery padding and view insets', (WidgetTester tester) async {