Fix `insetPadding` parameter nullability for dialogs (#143305)

fixes [`insetPadding` should be nullable in dialogs](https://github.com/flutter/flutter/issues/117125)

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

@@ -54,7 +54,7 @@ class Dialog extends StatelessWidget {
     this.surfaceTintColor,
     this.insetAnimationDuration = const Duration(milliseconds: 100),
     this.insetAnimationCurve = Curves.decelerate,
-    this.insetPadding = _defaultInsetPadding,
+    this.insetPadding,
     this.clipBehavior = Clip.none,
     this.shape,
     this.alignment,
@@ -215,7 +215,8 @@ class Dialog extends StatelessWidget {
   Widget build(BuildContext context) {
     final ThemeData theme = Theme.of(context);
     final DialogTheme dialogTheme = DialogTheme.of(context);
-    final EdgeInsets effectivePadding = MediaQuery.viewInsetsOf(context) + (insetPadding ?? EdgeInsets.zero);
+    final EdgeInsets effectivePadding = MediaQuery.viewInsetsOf(context)
+      + (insetPadding ?? dialogTheme.insetPadding ?? _defaultInsetPadding);
     final DialogTheme defaults = theme.useMaterial3
       ? (_fullscreen ? _DialogFullscreenDefaultsM3(context) : _DialogDefaultsM3(context))
       : _DialogDefaultsM2(context);
@@ -387,7 +388,7 @@ class AlertDialog extends StatelessWidget {
     this.shadowColor,
     this.surfaceTintColor,
     this.semanticLabel,
-    this.insetPadding = _defaultInsetPadding,
+    this.insetPadding,
     this.clipBehavior = Clip.none,
     this.shape,
     this.alignment,
@@ -676,7 +677,7 @@ class AlertDialog extends StatelessWidget {
   final String? semanticLabel;
 
   /// {@macro flutter.material.dialog.insetPadding}
-  final EdgeInsets insetPadding;
+  final EdgeInsets? insetPadding;
 
   /// {@macro flutter.material.dialog.clipBehavior}
   final Clip clipBehavior;
@@ -912,7 +913,7 @@ class _AdaptiveAlertDialog extends AlertDialog {
     super.shadowColor,
     super.surfaceTintColor,
     super.semanticLabel,
-    super.insetPadding = _defaultInsetPadding,
+    super.insetPadding,
     super.clipBehavior = Clip.none,
     super.shape,
     super.alignment,
@@ -1110,7 +1111,7 @@ class SimpleDialog extends StatelessWidget {
     this.shadowColor,
     this.surfaceTintColor,
     this.semanticLabel,
-    this.insetPadding = _defaultInsetPadding,
+    this.insetPadding,
     this.clipBehavior = Clip.none,
     this.shape,
     this.alignment,
@@ -1185,7 +1186,7 @@ class SimpleDialog extends StatelessWidget {
   final String? semanticLabel;
 
   /// {@macro flutter.material.dialog.insetPadding}
-  final EdgeInsets insetPadding;
+  final EdgeInsets? insetPadding;
 
   /// {@macro flutter.material.dialog.clipBehavior}
   final Clip clipBehavior;

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

@@ -39,6 +39,7 @@ class DialogTheme with Diagnosticable {
     this.contentTextStyle,
     this.actionsPadding,
     this.barrierColor,
+    this.insetPadding,
   });
 
   /// Overrides the default value for [Dialog.backgroundColor].
@@ -76,6 +77,9 @@ class DialogTheme with Diagnosticable {
   /// Overrides the default value for [barrierColor] in [showDialog].
   final Color? barrierColor;
 
+  /// Overrides the default value for [Dialog.insetPadding].
+  final EdgeInsets? insetPadding;
+
   /// Creates a copy of this object but with the given fields replaced with the
   /// new values.
   DialogTheme copyWith({
@@ -90,6 +94,7 @@ class DialogTheme with Diagnosticable {
     TextStyle? contentTextStyle,
     EdgeInsetsGeometry? actionsPadding,
     Color? barrierColor,
+    EdgeInsets? insetPadding,
   }) {
     return DialogTheme(
       backgroundColor: backgroundColor ?? this.backgroundColor,
@@ -103,6 +108,7 @@ class DialogTheme with Diagnosticable {
       contentTextStyle: contentTextStyle ?? this.contentTextStyle,
       actionsPadding: actionsPadding ?? this.actionsPadding,
       barrierColor: barrierColor ?? this.barrierColor,
+      insetPadding: insetPadding ?? this.insetPadding,
     );
   }
 
@@ -130,11 +136,25 @@ class DialogTheme with Diagnosticable {
       contentTextStyle: TextStyle.lerp(a?.contentTextStyle, b?.contentTextStyle, t),
       actionsPadding: EdgeInsetsGeometry.lerp(a?.actionsPadding, b?.actionsPadding, t),
       barrierColor: Color.lerp(a?.barrierColor, b?.barrierColor, t),
+      insetPadding: EdgeInsets.lerp(a?.insetPadding, b?.insetPadding, t),
     );
   }
 
   @override
-  int get hashCode => shape.hashCode;
+  int get hashCode => Object.hashAll(<Object?>[
+    backgroundColor,
+    elevation,
+    shadowColor,
+    surfaceTintColor,
+    shape,
+    alignment,
+    iconColor,
+    titleTextStyle,
+    contentTextStyle,
+    actionsPadding,
+    barrierColor,
+    insetPadding,
+  ]);
 
   @override
   bool operator ==(Object other) {
@@ -155,7 +175,8 @@ class DialogTheme with Diagnosticable {
         && other.titleTextStyle == titleTextStyle
         && other.contentTextStyle == contentTextStyle
         && other.actionsPadding == actionsPadding
-        && other.barrierColor == barrierColor;
+        && other.barrierColor == barrierColor
+        && other.insetPadding == insetPadding;
   }
 
   @override
@@ -172,5 +193,6 @@ class DialogTheme with Diagnosticable {
     properties.add(DiagnosticsProperty<TextStyle>('contentTextStyle', contentTextStyle, defaultValue: null));
     properties.add(DiagnosticsProperty<EdgeInsetsGeometry>('actionsPadding', actionsPadding, defaultValue: null));
     properties.add(ColorProperty('barrierColor', barrierColor));
+    properties.add(DiagnosticsProperty<EdgeInsets>('insetPadding', insetPadding, defaultValue: null));
   }
 }

packages/flutter/test/material/dialog_test.dart

@@ -1656,12 +1656,12 @@ void main() {
     // The default testing screen (800, 600)
     const Rect screenRect = Rect.fromLTRB(0.0, 0.0, 800.0, 600.0);
 
-    // Test with no padding
+    // Test with no padding.
     await tester.pumpWidget(
       const MediaQuery(
         data: MediaQueryData(),
         child: Dialog(
-          insetPadding: null,
+          insetPadding: EdgeInsets.zero,
           child: Placeholder(),
         ),
       ),
@@ -1669,7 +1669,7 @@ void main() {
     await tester.pumpAndSettle();
     expect(tester.getRect(find.byType(Placeholder)), screenRect);
 
-    // Test with an insetPadding
+    // Test with an insetPadding.
     await tester.pumpWidget(
       const MediaQuery(
         data: MediaQueryData(),
@@ -2841,6 +2841,21 @@ void main() {
     expect(okNode.hasFocus, false);
     expect(cancelNode.hasFocus, false);
   });
+
+  testWidgets('Dialog.insetPadding is nullable', (WidgetTester tester) async {
+    const Dialog dialog = Dialog();
+    expect(dialog.insetPadding, isNull);
+  });
+
+  testWidgets('AlertDialog.insetPadding is nullable', (WidgetTester tester) async {
+    const AlertDialog alertDialog = AlertDialog();
+    expect(alertDialog.insetPadding, isNull);
+  });
+
+  testWidgets('SimpleDialog.insetPadding is nullable', (WidgetTester tester) async {
+    const SimpleDialog simpleDialog = SimpleDialog();
+    expect(simpleDialog.insetPadding, isNull);
+  });
 }
 
 class _RestorableDialogTestWidget extends StatelessWidget {

packages/flutter/test/material/dialog_theme_test.dart

@@ -48,6 +48,11 @@ RenderParagraph _getTextRenderObject(WidgetTester tester, String text) {
 }
 
 void main() {
+  test('DialogTheme copyWith, ==, hashCode basics', () {
+    expect(const DialogTheme(), const DialogTheme().copyWith());
+    expect(const DialogTheme().hashCode, const DialogTheme().copyWith().hashCode);
+  });
+
   test('DialogTheme lerp special cases', () {
     expect(DialogTheme.lerp(null, null, 0), const DialogTheme());
     const DialogTheme theme = DialogTheme();
@@ -67,6 +72,7 @@ void main() {
       contentTextStyle: TextStyle(color: Color(0xff000000)),
       actionsPadding: EdgeInsets.all(8.0),
       barrierColor: Color(0xff000005),
+      insetPadding: EdgeInsets.all(20.0),
     ).debugFillProperties(builder);
     final List<String> description = builder.properties
         .where((DiagnosticsNode n) => !n.isFiltered(DiagnosticLevel.info))
@@ -82,6 +88,7 @@ void main() {
       'contentTextStyle: TextStyle(inherit: true, color: Color(0xff000000))',
       'actionsPadding: EdgeInsets.all(8.0)',
       'barrierColor: Color(0xff000005)',
+      'insetPadding: EdgeInsets.all(20.0)',
     ]);
   });
 
@@ -514,4 +521,31 @@ void main() {
     final ModalBarrier modalBarrier = tester.widget(find.byType(ModalBarrier).last);
     expect(modalBarrier.color, barrierColor);
   });
+
+  testWidgets('DialogTheme.insetPadding updates Dialog insetPadding', (WidgetTester tester) async {
+    // The default testing screen (800, 600)
+    const Rect screenRect = Rect.fromLTRB(0.0, 0.0, 800.0, 600.0);
+    const DialogTheme dialogTheme = DialogTheme(
+      insetPadding: EdgeInsets.fromLTRB(10, 15, 20, 25)
+    );
+    const Dialog dialog = Dialog(child: Placeholder());
+
+    await tester.pumpWidget(_appWithDialog(
+      tester,
+      dialog,
+      theme: ThemeData(dialogTheme: dialogTheme),
+    ));
+    await tester.tap(find.text('X'));
+    await tester.pump();
+
+    expect(
+      tester.getRect(find.byType(Placeholder)),
+      Rect.fromLTRB(
+        screenRect.left + dialogTheme.insetPadding!.left,
+        screenRect.top + dialogTheme.insetPadding!.top,
+        screenRect.right - dialogTheme.insetPadding!.right,
+        screenRect.bottom - dialogTheme.insetPadding!.bottom,
+      ),
+    );
+  });
 }