[Material] Add custom shape parameter for Dialogs. (#23443)

* [Material] Add custom shape parameter for Dialogs.

* [Material] Add custom shape parameter for Dialogs.

* Address Hans' first round comments.

* Address Hans' first round comments.

* Address Hans' Second round comments.

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

@@ -42,6 +42,7 @@ class Dialog extends StatelessWidget {
     this.child,
     this.insetAnimationDuration = const Duration(milliseconds: 100),
     this.insetAnimationCurve = Curves.decelerate,
+    this.shape,
   }) : super(key: key);
 
   /// The widget below this widget in the tree.
@@ -61,10 +62,23 @@ class Dialog extends StatelessWidget {
   /// Defaults to [Curves.fastOutSlowIn].
   final Curve insetAnimationCurve;
 
+  /// {@template flutter.material.dialog.shape}
+  /// The shape of this dialog's border.
+  ///
+  /// Defines the dialog's [Material.shape].
+  ///
+  /// The default shape is a [RoundedRectangleBorder] with a radius of 2.0.
+  /// {@endtemplate}
+  final ShapeBorder shape;
+
   Color _getColor(BuildContext context) {
     return Theme.of(context).dialogBackgroundColor;
   }
 
+  // TODO(johnsonmh): Update default dialog border radius to 4.0 to match material spec.
+  static const RoundedRectangleBorder _defaultDialogShape =
+    RoundedRectangleBorder(borderRadius: BorderRadius.all(Radius.circular(2.0)));
+
   @override
   Widget build(BuildContext context) {
     return AnimatedPadding(
@@ -85,6 +99,7 @@ class Dialog extends StatelessWidget {
               color: _getColor(context),
               type: MaterialType.card,
               child: child,
+              shape: shape ?? _defaultDialogShape,
             ),
           ),
         ),
@@ -172,6 +187,7 @@ class AlertDialog extends StatelessWidget {
     this.contentPadding = const EdgeInsets.fromLTRB(24.0, 20.0, 24.0, 24.0),
     this.actions,
     this.semanticLabel,
+    this.shape,
   }) : assert(contentPadding != null),
        super(key: key);
 
@@ -235,6 +251,9 @@ class AlertDialog extends StatelessWidget {
   ///    value is used.
   final String semanticLabel;
 
+  /// {@macro flutter.material.dialog.shape}
+  final ShapeBorder shape;
+
   @override
   Widget build(BuildContext context) {
     assert(debugCheckHasMaterialLocalizations(context));
@@ -295,7 +314,7 @@ class AlertDialog extends StatelessWidget {
         child: dialogChild
       );
 
-    return Dialog(child: dialogChild);
+    return Dialog(child: dialogChild, shape: shape);
   }
 }
 
@@ -440,6 +459,7 @@ class SimpleDialog extends StatelessWidget {
     this.children,
     this.contentPadding = const EdgeInsets.fromLTRB(0.0, 12.0, 0.0, 16.0),
     this.semanticLabel,
+    this.shape,
   }) : assert(titlePadding != null),
        assert(contentPadding != null),
        super(key: key);
@@ -494,6 +514,9 @@ class SimpleDialog extends StatelessWidget {
   ///    value is used.
   final String semanticLabel;
 
+  /// {@macro flutter.material.dialog.shape}
+  final ShapeBorder shape;
+
   @override
   Widget build(BuildContext context) {
     assert(debugCheckHasMaterialLocalizations(context));
@@ -546,7 +569,7 @@ class SimpleDialog extends StatelessWidget {
         label: label,
         child: dialogChild,
       );
-    return Dialog(child: dialogChild);
+    return Dialog(child: dialogChild, shape: shape);
   }
 }
 

packages/flutter/test/material/dialog_test.dart

@@ -10,12 +10,9 @@ import 'package:matcher/matcher.dart';
 
 import '../widgets/semantics_tester.dart';
 
-void main() {
-  testWidgets('Dialog is scrollable', (WidgetTester tester) async {
-    bool didPressOk = false;
-
-    await tester.pumpWidget(
-      MaterialApp(
+MaterialApp _appWithAlertDialog(WidgetTester tester, AlertDialog dialog, {ThemeData theme}) {
+  return MaterialApp(
+      theme: theme,
       home: Material(
         child: Builder(
           builder: (BuildContext context) {
@@ -26,7 +23,24 @@ void main() {
                   showDialog<void>(
                     context: context,
                     builder: (BuildContext context) {
-                        return AlertDialog(
+                        return dialog;
+                    },
+                  );
+                }
+              )
+            );
+          }
+        )
+      ),
+  );
+}
+
+const ShapeBorder _defaultDialogShape = RoundedRectangleBorder(borderRadius: BorderRadius.all(Radius.circular(2.0)));
+
+void main() {
+  testWidgets('Dialog is scrollable', (WidgetTester tester) async {
+    bool didPressOk = false;
+    final AlertDialog dialog = AlertDialog(
       content: Container(
         height: 5000.0,
         width: 300.0,
@@ -41,16 +55,7 @@ void main() {
         )
       ],
     );
-                      },
-                    );
-                  }
-                )
-              );
-            }
-          )
-        )
-      )
-    );
+    await tester.pumpWidget(_appWithAlertDialog(tester, dialog));
 
     await tester.tap(find.text('X'));
     await tester.pump(); // start animation
@@ -62,46 +67,76 @@ void main() {
   });
 
   testWidgets('Dialog background color', (WidgetTester tester) async {
-
-    await tester.pumpWidget(
-      MaterialApp(
-        theme: ThemeData(brightness: Brightness.dark),
-        home: Material(
-          child: Builder(
-            builder: (BuildContext context) {
-              return Center(
-                child: RaisedButton(
-                  child: const Text('X'),
-                  onPressed: () {
-                    showDialog<void>(
-                      context: context,
-                      builder: (BuildContext context) {
-                        return const AlertDialog(
+    const AlertDialog dialog = AlertDialog(
       title: Text('Title'),
       content: Text('Y'),
       actions: <Widget>[ ],
     );
-                      },
+    await tester.pumpWidget(_appWithAlertDialog(tester, dialog, theme: ThemeData(brightness: Brightness.dark)));
+
+    await tester.tap(find.text('X'));
+    await tester.pump(); // start animation
+    await tester.pump(const Duration(seconds: 1));
+
+    final StatefulElement widget = tester.element(
+        find.descendant(of: find.byType(AlertDialog), matching: find.byType(Material)));
+    final Material materialWidget = widget.state.widget;
+    expect(materialWidget.color, Colors.grey[800]);
+    expect(materialWidget.shape, _defaultDialogShape);
+  });
+
+  testWidgets('Custom dialog shape', (WidgetTester tester) async {
+    const RoundedRectangleBorder customBorder =
+      RoundedRectangleBorder(borderRadius: BorderRadius.all(Radius.circular(16.0)));
+    const AlertDialog dialog = AlertDialog(
+      actions: <Widget>[ ],
+      shape: customBorder,
     );
-                  },
-                ),
+    await tester.pumpWidget(_appWithAlertDialog(tester, dialog));
+
+    await tester.tap(find.text('X'));
+    await tester.pump(); // start animation
+    await tester.pump(const Duration(seconds: 1));
+
+    final StatefulElement widget = tester.element(
+        find.descendant(of: find.byType(AlertDialog), matching: find.byType(Material)));
+    final Material materialWidget = widget.state.widget;
+    expect(materialWidget.shape, customBorder);
+  });
+
+  testWidgets('Null dialog shape', (WidgetTester tester) async {
+    const AlertDialog dialog = AlertDialog(
+      actions: <Widget>[ ],
+      shape: null,
     );
-            },
-          ),
-        ),
-      ),
+    await tester.pumpWidget(_appWithAlertDialog(tester, dialog));
+
+    await tester.tap(find.text('X'));
+    await tester.pump(); // start animation
+    await tester.pump(const Duration(seconds: 1));
+
+    final StatefulElement widget = tester.element(
+        find.descendant(of: find.byType(AlertDialog), matching: find.byType(Material)));
+    final Material materialWidget = widget.state.widget;
+    expect(materialWidget.shape, _defaultDialogShape);
+  });
+
+  testWidgets('Rectangular dialog shape', (WidgetTester tester) async {
+    const ShapeBorder customBorder = Border();
+    const AlertDialog dialog = AlertDialog(
+      actions: <Widget>[ ],
+      shape: customBorder,
     );
+    await tester.pumpWidget(_appWithAlertDialog(tester, dialog));
 
     await tester.tap(find.text('X'));
     await tester.pump(); // start animation
     await tester.pump(const Duration(seconds: 1));
 
-    final StatefulElement widget = tester.element(find.byType(Material).last);
+    final StatefulElement widget = tester.element(
+        find.descendant(of: find.byType(AlertDialog), matching: find.byType(Material)));
     final Material materialWidget = widget.state.widget;
-    //first and second expect check that the material is the dialog's one
-    expect(materialWidget.type, MaterialType.card);
-    expect(materialWidget.elevation, 24);
-    expect(materialWidget.color, Colors.grey[800]);
+    expect(materialWidget.shape, customBorder);
   });
 
   testWidgets('Simple dialog control test', (WidgetTester tester) async {