add diagnosticable mixin

com.unity.uiwidgets/Runtime/foundation/diagnostics.cs

         }
     }
 
-    public class DiagnosticableNode<T> : DiagnosticsNode where T : Diagnosticable {
+    public class DiagnosticableNode<T> : DiagnosticsNode where T : IDiagnosticable {
-            T value = null,
+            T value = default,
             DiagnosticsTreeStyle? style = null
         ) : base(name: name, style: style) {
             D.assert(value != null);
         public string emptyBodyDescription;
     }
 
-    public abstract class Diagnosticable {
+    public interface IDiagnosticable {
+        string toStringShort();
+
+        string toString(DiagnosticLevel minLevel = DiagnosticLevel.debug);
+
+        DiagnosticsNode toDiagnosticsNode(
+            string name = null,
+            DiagnosticsTreeStyle style = DiagnosticsTreeStyle.sparse);
+
+        void debugFillProperties(DiagnosticPropertiesBuilder properties);
+    }
+
+    public abstract class Diagnosticable : IDiagnosticable {
         protected Diagnosticable() {
         }
 

com.unity.uiwidgets/Runtime/foundation/diagnosticable.mixin.gen.cs

+namespace Unity.UIWidgets.foundation {
+    public class DiagnosticableMixinChangeNotifier : ChangeNotifier, IDiagnosticable {
+        protected DiagnosticableMixinChangeNotifier() {
+        }
+
+        public virtual string toStringShort() {
+            return foundation_.describeIdentity(this);
+        }
+
+        public override string ToString() {
+            return toString();
+        }
+
+        public virtual string toString(DiagnosticLevel minLevel = DiagnosticLevel.debug) {
+            string fullString = null;
+            D.assert(() => {
+                fullString = toDiagnosticsNode(style: DiagnosticsTreeStyle.singleLine)
+                    .toString(minLevel: minLevel);
+                return true;
+            });
+            return fullString ?? toStringShort();
+        }
+
+        public virtual DiagnosticsNode toDiagnosticsNode(
+            string name = null,
+            DiagnosticsTreeStyle style = DiagnosticsTreeStyle.sparse) {
+            return new DiagnosticableNode<DiagnosticableMixinChangeNotifier>(
+                name: name, value: this, style: style
+            );
+        }
+
+        public virtual void debugFillProperties(DiagnosticPropertiesBuilder properties) {
+        }
+    }
+
+}
+

com.unity.uiwidgets/Runtime/foundation/diagnosticable.mixin.njk

+namespace Unity.UIWidgets.foundation {
+{% macro DiagnosticableMixin(with) %}
+    {% set className = 'DiagnosticableMixin' + with %}
+    public class {{className}} : {{with}}, IDiagnosticable {
+        protected {{className}}() {
+        }
+
+        public virtual string toStringShort() {
+            return foundation_.describeIdentity(this);
+        }
+
+        public override string ToString() {
+            return toString();
+        }
+
+        public virtual string toString(DiagnosticLevel minLevel = DiagnosticLevel.debug) {
+            string fullString = null;
+            D.assert(() => {
+                fullString = toDiagnosticsNode(style: DiagnosticsTreeStyle.singleLine)
+                    .toString(minLevel: minLevel);
+                return true;
+            });
+            return fullString ?? toStringShort();
+        }
+
+        public virtual DiagnosticsNode toDiagnosticsNode(
+            string name = null,
+            DiagnosticsTreeStyle style = DiagnosticsTreeStyle.sparse) {
+            return new DiagnosticableNode<{{className}}>(
+                name: name, value: this, style: style
+            );
+        }
+
+        public virtual void debugFillProperties(DiagnosticPropertiesBuilder properties) {
+        }
+    }
+{% endmacro %}
+{{ DiagnosticableMixin('ChangeNotifier') }}
+}
+