Update ThemeData.dialogTheme type to accept DialogThemeData (#155129)

Following flutter/flutter#153982, this PR is to normalize `ThemeData.dialogTheme`; change the `DialogTheme dialogTheme` property to `DialogThemeData dialogTheme` in ThemeData. In `ThemeData()` and `ThemeData.copyWith()`, the dialogTheme parameter type is changed to `Object?` to accept both `DialogTheme` and `DialogThemeData` so that we won't cause immediate breaking change and make sure rolling is smooth. Once all component themes are normalized, these `Object?` types should be changed to `xxxThemeData`.

There's no way to create a dart fix because we can't add a "@deprecated" label for `DialogTheme`; `DialogTheme` is a new `InheritedWidget` subclass now.

Addresses the "theme normalization" sub project within flutter/flutter#91772

Author: QuncCccccc

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

@@ -707,7 +707,7 @@ class _DatePickerDialogState extends State<DatePickerDialog> with RestorationMix
     // layout issues.
     final double textScaleFactor = MediaQuery.textScalerOf(context).clamp(maxScaleFactor: _kMaxTextScaleFactor).scale(_fontSizeToScale) / _fontSizeToScale;
     final Size dialogSize = _dialogSize(context) * textScaleFactor;
-    final DialogTheme dialogTheme = theme.dialogTheme;
+    final DialogThemeData dialogTheme = theme.dialogTheme;
     return Dialog(
       backgroundColor: datePickerTheme.backgroundColor ?? defaults.backgroundColor,
       elevation: useMaterial3
@@ -1660,7 +1660,7 @@ class _DateRangePickerDialogState extends State<DateRangePickerDialog> with Rest
               : localizations.dateRangePickerHelpText.toUpperCase()
           ),
         );
-        final DialogTheme dialogTheme = theme.dialogTheme;
+        final DialogThemeData dialogTheme = theme.dialogTheme;
         size = orientation == Orientation.portrait
           ? (useMaterial3 ? _inputPortraitDialogSizeM3 : _inputPortraitDialogSizeM2)
           : _inputRangeLandscapeDialogSize;

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

@@ -230,7 +230,7 @@ class Dialog extends StatelessWidget {
   @override
   Widget build(BuildContext context) {
     final ThemeData theme = Theme.of(context);
-    final DialogThemeData dialogTheme = DialogTheme.of(context).data;
+    final DialogThemeData dialogTheme = DialogTheme.of(context);
     final EdgeInsets effectivePadding = MediaQuery.viewInsetsOf(context)
       + (insetPadding ?? dialogTheme.insetPadding ?? _defaultInsetPadding);
     final DialogThemeData defaults = theme.useMaterial3
@@ -720,7 +720,7 @@ class AlertDialog extends StatelessWidget {
     assert(debugCheckHasMaterialLocalizations(context));
     final ThemeData theme = Theme.of(context);
 
-    final DialogThemeData dialogTheme = DialogTheme.of(context).data;
+    final DialogThemeData dialogTheme = DialogTheme.of(context);
     final DialogThemeData defaults = theme.useMaterial3 ? _DialogDefaultsM3(context) : _DialogDefaultsM2(context);
 
     String? label = semanticLabel;
@@ -1235,7 +1235,7 @@ class SimpleDialog extends StatelessWidget {
 
     // The paddingScaleFactor is used to adjust the padding of Dialog
     // children.
-    final TextStyle defaultTextStyle = titleTextStyle ?? DialogTheme.of(context).data.titleTextStyle ?? theme.textTheme.titleLarge!;
+    final TextStyle defaultTextStyle = titleTextStyle ?? DialogTheme.of(context).titleTextStyle ?? theme.textTheme.titleLarge!;
     final double fontSize = defaultTextStyle.fontSize ?? kDefaultFontSize;
     final double fontSizeToScale = fontSize == 0.0 ? kDefaultFontSize : fontSize;
     final double effectiveTextScale = MediaQuery.textScalerOf(context).scale(fontSizeToScale) / fontSizeToScale;
@@ -1445,7 +1445,7 @@ Future<T?> showDialog<T>({
     builder: builder,
     barrierColor: barrierColor
       ?? DialogTheme.of(context).barrierColor
-      ?? Theme.of(context).dialogTheme.data.barrierColor
+      ?? Theme.of(context).dialogTheme.barrierColor
       ?? Colors.black54,
     barrierDismissible: barrierDismissible,
     barrierLabel: barrierLabel,

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

@@ -190,9 +190,9 @@ class DialogTheme extends InheritedTheme with Diagnosticable {
   }
 
   /// The [ThemeData.dialogTheme] property of the ambient [Theme].
-  static DialogTheme of(BuildContext context) {
+  static DialogThemeData of(BuildContext context) {
     final DialogTheme? dialogTheme = context.dependOnInheritedWidgetOfExactType<DialogTheme>();
-    return dialogTheme ?? Theme.of(context).dialogTheme;
+    return dialogTheme?.data ?? Theme.of(context).dialogTheme;
   }
 
   @override

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

@@ -320,7 +320,8 @@ class ThemeData with Diagnosticable {
     ChipThemeData? chipTheme,
     DataTableThemeData? dataTableTheme,
     DatePickerThemeData? datePickerTheme,
-    DialogTheme? dialogTheme,
+    // TODO(QuncCccccc): Change the parameter type to DialogThemeData
+    Object? dialogTheme,
     DividerThemeData? dividerTheme,
     DrawerThemeData? drawerTheme,
     DropdownMenuThemeData? dropdownMenuTheme,
@@ -497,7 +498,15 @@ class ThemeData with Diagnosticable {
     chipTheme ??= const ChipThemeData();
     dataTableTheme ??= const DataTableThemeData();
     datePickerTheme ??= const DatePickerThemeData();
-    dialogTheme ??= const DialogTheme();
+    // TODO(QuncCccccc): Clean this up once the type of `dialogTheme` is changed to `DialogThemeData`
+    if (dialogTheme != null) {
+      if (dialogTheme is DialogTheme) {
+        dialogTheme = dialogTheme.data;
+      } else if (dialogTheme is! DialogThemeData) {
+        throw ArgumentError('dialogTheme must be either a DialogThemeData or a DialogTheme');
+      }
+    }
+    dialogTheme ??= const DialogThemeData();
     dividerTheme ??= const DividerThemeData();
     drawerTheme ??= const DrawerThemeData();
     dropdownMenuTheme ??= const DropdownMenuThemeData();
@@ -590,7 +599,7 @@ class ThemeData with Diagnosticable {
       chipTheme: chipTheme,
       dataTableTheme: dataTableTheme,
       datePickerTheme: datePickerTheme,
-      dialogTheme: dialogTheme,
+      dialogTheme: dialogTheme as DialogThemeData,
       dividerTheme: dividerTheme,
       drawerTheme: drawerTheme,
       dropdownMenuTheme: dropdownMenuTheme,
@@ -1276,7 +1285,7 @@ class ThemeData with Diagnosticable {
   final DatePickerThemeData datePickerTheme;
 
   /// A theme for customizing the shape of a dialog.
-  final DialogTheme dialogTheme;
+  final DialogThemeData dialogTheme;
 
   /// A theme for customizing the color, thickness, and indents of [Divider]s,
   /// [VerticalDivider]s, etc.
@@ -1462,7 +1471,8 @@ class ThemeData with Diagnosticable {
     ChipThemeData? chipTheme,
     DataTableThemeData? dataTableTheme,
     DatePickerThemeData? datePickerTheme,
-    DialogTheme? dialogTheme,
+    // TODO(QuncCccccc): Change the parameter type to DialogThemeData
+    Object? dialogTheme,
     DividerThemeData? dividerTheme,
     DrawerThemeData? drawerTheme,
     DropdownMenuThemeData? dropdownMenuTheme,
@@ -1510,6 +1520,15 @@ class ThemeData with Diagnosticable {
     ButtonBarThemeData? buttonBarTheme,
   }) {
     cupertinoOverrideTheme = cupertinoOverrideTheme?.noDefault();
+
+    // TODO(QuncCccccc): Clean this up once the type of `dialogTheme` is changed to `DialogThemeData`
+    if (dialogTheme != null) {
+      if (dialogTheme is DialogTheme) {
+        dialogTheme = dialogTheme.data;
+      } else if (dialogTheme is! DialogThemeData) {
+        throw ArgumentError('dialogTheme must be either a DialogThemeData or a DialogTheme');
+      }
+    }
     return ThemeData.raw(
       // For the sanity of the reader, make sure these properties are in the same
       // order in every place that they are separated by section comments (e.g.
@@ -1571,7 +1590,7 @@ class ThemeData with Diagnosticable {
       chipTheme: chipTheme ?? this.chipTheme,
       dataTableTheme: dataTableTheme ?? this.dataTableTheme,
       datePickerTheme: datePickerTheme ?? this.datePickerTheme,
-      dialogTheme: dialogTheme ?? this.dialogTheme,
+      dialogTheme: dialogTheme as DialogThemeData? ?? this.dialogTheme,
       dividerTheme: dividerTheme ?? this.dividerTheme,
       drawerTheme: drawerTheme ?? this.drawerTheme,
       dropdownMenuTheme: dropdownMenuTheme ?? this.dropdownMenuTheme,
@@ -1764,7 +1783,7 @@ class ThemeData with Diagnosticable {
       chipTheme: ChipThemeData.lerp(a.chipTheme, b.chipTheme, t)!,
       dataTableTheme: DataTableThemeData.lerp(a.dataTableTheme, b.dataTableTheme, t),
       datePickerTheme: DatePickerThemeData.lerp(a.datePickerTheme, b.datePickerTheme, t),
-      dialogTheme: DialogTheme.lerp(a.dialogTheme, b.dialogTheme, t),
+      dialogTheme: DialogThemeData.lerp(a.dialogTheme, b.dialogTheme, t),
       dividerTheme: DividerThemeData.lerp(a.dividerTheme, b.dividerTheme, t),
       drawerTheme: DrawerThemeData.lerp(a.drawerTheme, b.drawerTheme, t)!,
       dropdownMenuTheme: DropdownMenuThemeData.lerp(a.dropdownMenuTheme, b.dropdownMenuTheme, t),
@@ -2062,7 +2081,7 @@ class ThemeData with Diagnosticable {
     properties.add(DiagnosticsProperty<ChipThemeData>('chipTheme', chipTheme, level: DiagnosticLevel.debug));
     properties.add(DiagnosticsProperty<DataTableThemeData>('dataTableTheme', dataTableTheme, defaultValue: defaultData.dataTableTheme, level: DiagnosticLevel.debug));
     properties.add(DiagnosticsProperty<DatePickerThemeData>('datePickerTheme', datePickerTheme, defaultValue: defaultData.datePickerTheme, level: DiagnosticLevel.debug));
-    properties.add(DiagnosticsProperty<DialogTheme>('dialogTheme', dialogTheme, defaultValue: defaultData.dialogTheme, level: DiagnosticLevel.debug));
+    properties.add(DiagnosticsProperty<DialogThemeData>('dialogTheme', dialogTheme, defaultValue: defaultData.dialogTheme, level: DiagnosticLevel.debug));
     properties.add(DiagnosticsProperty<DividerThemeData>('dividerTheme', dividerTheme, defaultValue: defaultData.dividerTheme, level: DiagnosticLevel.debug));
     properties.add(DiagnosticsProperty<DrawerThemeData>('drawerTheme', drawerTheme, defaultValue: defaultData.drawerTheme, level: DiagnosticLevel.debug));
     properties.add(DiagnosticsProperty<DropdownMenuThemeData>('dropdownMenuTheme', dropdownMenuTheme, defaultValue: defaultData.dropdownMenuTheme, level: DiagnosticLevel.debug));

packages/flutter/test/material/date_picker_test.dart

@@ -603,7 +603,7 @@ void main() {
       expect(defaultDialogMaterial.elevation, datePickerDefaultDialogTheme.elevation);
 
       // Test that it honors ThemeData.dialogTheme settings
-      const DialogTheme customDialogTheme = DialogTheme(
+      const DialogThemeData customDialogTheme = DialogThemeData(
         shape: RoundedRectangleBorder(
           borderRadius: BorderRadius.all(Radius.circular(40.0)),
         ),