Make SlottedMultiChildRenderObjectWidgetMixin a concrete class (#126108)

This is a proof of concept for renaming SlottedMultiChildRenderObjectWidgetMixin to SlottedMultiChildRenderObjectWidget and making it a concrete class.

I also made SlottedContainerRenderObjectMixin generic instead of being specialized to RenderBox.

I don't think this is something we can easily automigrate, but we may not need to, I don't know how common this is...

examples/api/lib/widgets/slotted_render_object_widget/slotted_multi_child_render_object_widget_mixin.0.dart

@@ -5,7 +5,7 @@
 import 'package:flutter/material.dart';
 import 'package:flutter/rendering.dart';
 
-/// Flutter code sample for [SlottedMultiChildRenderObjectWidgetMixin].
+/// Flutter code sample for [SlottedMultiChildRenderObjectWidget].
 
 /// Slots used for the children of [Diagonal] and [RenderDiagonal].
 enum DiagonalSlot {
@@ -14,9 +14,9 @@ enum DiagonalSlot {
 }
 
 /// A widget that demonstrates the usage of
-/// [SlottedMultiChildRenderObjectWidgetMixin] by providing slots for two
+/// [SlottedMultiChildRenderObjectWidget] by providing slots for two
 /// children that will be arranged diagonally.
-class Diagonal extends RenderObjectWidget with SlottedMultiChildRenderObjectWidgetMixin<DiagonalSlot> {
+class Diagonal extends SlottedMultiChildRenderObjectWidget<DiagonalSlot, RenderBox> {
   const Diagonal({
     super.key,
     this.topLeft,
@@ -49,7 +49,7 @@ class Diagonal extends RenderObjectWidget with SlottedMultiChildRenderObjectWidg
   // [SlottedRenderObjectElement.update].
 
   @override
-  SlottedContainerRenderObjectMixin<DiagonalSlot> createRenderObject(
+  SlottedContainerRenderObjectMixin<DiagonalSlot, RenderBox> createRenderObject(
     BuildContext context,
   ) {
     return RenderDiagonal(
@@ -60,7 +60,7 @@ class Diagonal extends RenderObjectWidget with SlottedMultiChildRenderObjectWidg
   @override
   void updateRenderObject(
     BuildContext context,
-    SlottedContainerRenderObjectMixin<DiagonalSlot> renderObject,
+    SlottedContainerRenderObjectMixin<DiagonalSlot, RenderBox> renderObject,
   ) {
     (renderObject as RenderDiagonal).backgroundColor = backgroundColor;
   }
@@ -70,7 +70,7 @@ class Diagonal extends RenderObjectWidget with SlottedMultiChildRenderObjectWidg
 /// [SlottedContainerRenderObjectMixin] by providing slots for two children that
 /// will be arranged diagonally.
 class RenderDiagonal extends RenderBox
-    with SlottedContainerRenderObjectMixin<DiagonalSlot>, DebugOverflowIndicatorMixin {
+    with SlottedContainerRenderObjectMixin<DiagonalSlot, RenderBox>, DebugOverflowIndicatorMixin {
   RenderDiagonal({Color? backgroundColor}) : _backgroundColor = backgroundColor;
 
   // Getters and setters to configure the [RenderObject] with the configuration

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

@@ -1342,7 +1342,7 @@ class _RenderChipRedirectingHitDetection extends RenderConstrainedBox {
   }
 }
 
-class _ChipRenderWidget extends RenderObjectWidget with SlottedMultiChildRenderObjectWidgetMixin<_ChipSlot> {
+class _ChipRenderWidget extends SlottedMultiChildRenderObjectWidget<_ChipSlot, RenderBox> {
   const _ChipRenderWidget({
     required this.theme,
     this.value,
@@ -1393,7 +1393,7 @@ class _ChipRenderWidget extends RenderObjectWidget with SlottedMultiChildRenderO
   }
 
   @override
-  SlottedContainerRenderObjectMixin<_ChipSlot> createRenderObject(BuildContext context) {
+  SlottedContainerRenderObjectMixin<_ChipSlot, RenderBox> createRenderObject(BuildContext context) {
     return _RenderChip(
       theme: theme,
       textDirection: Directionality.of(context),
@@ -1478,7 +1478,7 @@ class _ChipRenderTheme {
   );
 }
 
-class _RenderChip extends RenderBox with SlottedContainerRenderObjectMixin<_ChipSlot> {
+class _RenderChip extends RenderBox with SlottedContainerRenderObjectMixin<_ChipSlot, RenderBox> {
   _RenderChip({
     required _ChipRenderTheme theme,
     required TextDirection textDirection,

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

@@ -693,7 +693,7 @@ class _RenderDecorationLayout {
 }
 
 // The workhorse: layout and paint a _Decorator widget's _Decoration.
-class _RenderDecoration extends RenderBox with SlottedContainerRenderObjectMixin<_DecorationSlot> {
+class _RenderDecoration extends RenderBox with SlottedContainerRenderObjectMixin<_DecorationSlot, RenderBox> {
   _RenderDecoration({
     required _Decoration decoration,
     required TextDirection textDirection,
@@ -1637,7 +1637,7 @@ class _RenderDecoration extends RenderBox with SlottedContainerRenderObjectMixin
   }
 }
 
-class _Decorator extends RenderObjectWidget with SlottedMultiChildRenderObjectWidgetMixin<_DecorationSlot> {
+class _Decorator extends SlottedMultiChildRenderObjectWidget<_DecorationSlot, RenderBox> {
   const _Decorator({
     required this.textAlignVertical,
     required this.decoration,

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

@@ -967,7 +967,7 @@ enum _ListTileSlot {
   trailing,
 }
 
-class _ListTile extends RenderObjectWidget with SlottedMultiChildRenderObjectWidgetMixin<_ListTileSlot> {
+class _ListTile extends SlottedMultiChildRenderObjectWidget<_ListTileSlot, RenderBox> {
   const _ListTile({
     this.leading,
     required this.title,
@@ -1049,7 +1049,7 @@ class _ListTile extends RenderObjectWidget with SlottedMultiChildRenderObjectWid
   }
 }
 
-class _RenderListTile extends RenderBox with SlottedContainerRenderObjectMixin<_ListTileSlot> {
+class _RenderListTile extends RenderBox with SlottedContainerRenderObjectMixin<_ListTileSlot, RenderBox> {
   _RenderListTile({
     required bool isDense,
     required VisualDensity visualDensity,

packages/flutter/lib/src/widgets/framework.dart

@@ -1760,7 +1760,7 @@ abstract class InheritedWidget extends ProxyWidget {
 ///
 ///  * [MultiChildRenderObjectWidget], which configures a [RenderObject] with
 ///    a single list of children.
-///  * [SlottedMultiChildRenderObjectWidgetMixin], which configures a
+///  * [SlottedMultiChildRenderObjectWidget], which configures a
 ///    [RenderObject] that organizes its children in different named slots.
 abstract class RenderObjectWidget extends Widget {
   /// Abstract const constructor. This constructor enables subclasses to provide
@@ -1854,7 +1854,7 @@ abstract class SingleChildRenderObjectWidget extends RenderObjectWidget {
 ///  * [Stack], which uses [MultiChildRenderObjectWidget].
 ///  * [RenderStack], for an example implementation of the associated render
 ///    object.
-///  * [SlottedMultiChildRenderObjectWidgetMixin], which configures a
+///  * [SlottedMultiChildRenderObjectWidget], which configures a
 ///    [RenderObject] that instead of having a single list of children organizes
 ///    its children in named slots.
 abstract class MultiChildRenderObjectWidget extends RenderObjectWidget {

packages/flutter/test/widgets/slotted_render_object_widget_test.dart

@@ -269,7 +269,7 @@ enum _DiagonalSlot {
   bottomRight,
 }
 
-class _Diagonal extends RenderObjectWidget with SlottedMultiChildRenderObjectWidgetMixin<_DiagonalSlot?> {
+class _Diagonal extends RenderObjectWidget with SlottedMultiChildRenderObjectWidgetMixin<_DiagonalSlot?, RenderBox> {
   const _Diagonal({
     this.topLeft,
     this.bottomRight,
@@ -296,14 +296,14 @@ class _Diagonal extends RenderObjectWidget with SlottedMultiChildRenderObjectWid
   }
 
   @override
-  SlottedContainerRenderObjectMixin<_DiagonalSlot?> createRenderObject(
+  SlottedContainerRenderObjectMixin<_DiagonalSlot?, RenderBox> createRenderObject(
     BuildContext context,
   ) {
     return _RenderDiagonal();
   }
 }
 
-class _RenderDiagonal extends RenderBox with SlottedContainerRenderObjectMixin<_DiagonalSlot?> {
+class _RenderDiagonal extends RenderBox with SlottedContainerRenderObjectMixin<_DiagonalSlot?, RenderBox> {
   RenderBox? get _topLeft => childForSlot(_DiagonalSlot.topLeft);
   RenderBox? get _bottomRight => childForSlot(_DiagonalSlot.bottomRight);
   RenderBox? get _nullSlot => childForSlot(null);
@@ -370,6 +370,6 @@ class _Slot {
   String toString() => describeIdentity(this);
 }
 
-class _RenderTest extends RenderBox with SlottedContainerRenderObjectMixin<_Slot> {
+class _RenderTest extends RenderBox with SlottedContainerRenderObjectMixin<_Slot, RenderBox> {
   String publicNameForSlot(_Slot slot) => debugNameForSlot(slot);
 }