Material Date Picker should honor DialogTheme shape, and elevation. (#53713)

* Date Picker should honor DialogTheme shape, and elevation.

packages/flutter/lib/src/material/pickers/date_picker_dialog.dart

@@ -12,6 +12,7 @@ import '../button_theme.dart';
 import '../color_scheme.dart';
 import '../debug.dart';
 import '../dialog.dart';
+import '../dialog_theme.dart';
 import '../flat_button.dart';
 import '../icons.dart';
 import '../material_localizations.dart';
@@ -427,6 +428,7 @@ class _DatePickerDialogState extends State<_DatePickerDialog> {
     );
 
     final Size dialogSize = _dialogSize(context) * textScaleFactor;
+    final DialogTheme dialogTheme = Theme.of(context).dialogTheme;
     return Dialog(
       child: AnimatedContainer(
         width: dialogSize.width,
@@ -473,11 +475,13 @@ class _DatePickerDialogState extends State<_DatePickerDialog> {
         ),
       ),
       insetPadding: const EdgeInsets.symmetric(horizontal: 16.0, vertical: 24.0),
-      shape: const RoundedRectangleBorder(
+      // The default dialog shape is radius 2 rounded rect, but the spec has
+      // been updated to 4, so we will use that here for the Date Picker, but
+      // only if there isn't one provided in the theme.
+      shape: dialogTheme.shape ?? const RoundedRectangleBorder(
         borderRadius: BorderRadius.all(Radius.circular(4.0))
       ),
       clipBehavior: Clip.antiAlias,
-      elevation: 24.0,
     );
   }
 }

packages/flutter/test/material/date_picker_test.dart

@@ -247,6 +247,77 @@ void main() {
       expect(nestedObserver.datePickerCount, 1);
     });
 
+    testWidgets('honors DialogTheme for shape and elevation', (WidgetTester tester) async {
+      // Test that the defaults work
+      const DialogTheme datePickerDefaultDialogTheme = DialogTheme(
+        shape: RoundedRectangleBorder(
+          borderRadius: BorderRadius.all(Radius.circular(4.0))
+        ),
+        elevation: 24,
+      );
+      await tester.pumpWidget(
+        MaterialApp(
+          home: Center(
+            child: Builder(
+              builder: (BuildContext context) {
+                return RaisedButton(
+                  child: const Text('X'),
+                  onPressed: () {
+                    showDatePicker(
+                      context: context,
+                      initialDate: DateTime.now(),
+                      firstDate: DateTime(2018),
+                      lastDate: DateTime(2030),
+                    );
+                  },
+                );
+              },
+            ),
+          ),
+        ),
+      );
+      await tester.tap(find.text('X'));
+      await tester.pumpAndSettle();
+      final Material defaultDialogMaterial = tester.widget<Material>(find.descendant(of: find.byType(Dialog), matching: find.byType(Material)).first);
+      expect(defaultDialogMaterial.shape, datePickerDefaultDialogTheme.shape);
+      expect(defaultDialogMaterial.elevation, datePickerDefaultDialogTheme.elevation);
+
+      // Test that it honors ThemeData.dialogTheme settings
+      const DialogTheme customDialogTheme = DialogTheme(
+        shape: RoundedRectangleBorder(
+          borderRadius: BorderRadius.all(Radius.circular(40.0))
+        ),
+        elevation: 50,
+      );
+      await tester.pumpWidget(
+        MaterialApp(
+          theme: ThemeData.fallback().copyWith(dialogTheme: customDialogTheme),
+          home: Center(
+            child: Builder(
+              builder: (BuildContext context) {
+                return RaisedButton(
+                  child: const Text('X'),
+                  onPressed: () {
+                    showDatePicker(
+                      context: context,
+                      initialDate: DateTime.now(),
+                      firstDate: DateTime(2018),
+                      lastDate: DateTime(2030),
+                    );
+                  },
+                );
+              },
+            ),
+          ),
+        ),
+      );
+      await tester.tap(find.text('X'));
+      await tester.pumpAndSettle();
+      final Material themeDialogMaterial = tester.widget<Material>(find.descendant(of: find.byType(Dialog), matching: find.byType(Material)).first);
+      expect(themeDialogMaterial.shape, customDialogTheme.shape);
+      expect(themeDialogMaterial.elevation, customDialogTheme.elevation);
+    });
+
   });
 
   group('Calendar mode', () {