Add implementation advice to debugTypicalAncestorWidgetClass (#130530)

Fixes flutter/flutter#56500

Author: Hixie

packages/flutter/lib/src/rendering/paragraph.dart

@@ -71,7 +71,7 @@ class TextParentData extends ParentData with ContainerParentDataMixin<RenderBox>
   }
 
   @override
-  String toString() =>'widget: $span, ${offset == null ? "not laid out" : "offset: $offset"}';
+  String toString() => 'widget: $span, ${offset == null ? "not laid out" : "offset: $offset"}';
 }
 
 /// A mixin that provides useful default behaviors for text [RenderBox]es

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

@@ -1514,7 +1514,20 @@ abstract class ParentDataWidget<T extends ParentData> extends ProxyWidget {
   /// that [applyParentData] will write to.
   ///
   /// This is only used in error messages to tell users what widget typically
-  /// wraps this ParentDataWidget.
+  /// wraps this [ParentDataWidget].
+  ///
+  /// ## Implementations
+  ///
+  /// The returned type should be a subclass of `RenderObjectWidget`.
+  ///
+  /// ```dart
+  ///   @override
+  ///   Type get debugTypicalAncestorWidgetClass => FrogJar;
+  /// ```
+  ///
+  /// If the "typical" parent is generic (`Foo<T>`), consider specifying either
+  /// a typical type argument (e.g. `Foo<int>` if `int` is typically how the
+  /// type is specialized), or specifying the upper bound (e.g. `Foo<Object?>`).
   Type get debugTypicalAncestorWidgetClass;
 
   Iterable<DiagnosticsNode> _debugDescribeIncorrectParentDataType({

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

@@ -290,7 +290,7 @@ class _WidgetSpanParentData extends ParentDataWidget<TextParentData> {
   }
 
   @override
-  Type get debugTypicalAncestorWidgetClass => RenderInlineChildrenContainerDefaults;
+  Type get debugTypicalAncestorWidgetClass => RichText;
 }
 
 // A RenderObjectWidget that automatically applies text scaling on inline