Add option to track widget rebuilds and repaints from the Flutter inspector. (#23534)

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

@@ -5,6 +5,8 @@
 import 'package:flutter/foundation.dart';
 import 'package:flutter/painting.dart';
 
+import 'object.dart';
+
 export 'package:flutter/foundation.dart' show debugPrint;
 
 // Any changes to this file should be reflected in the debugAssertAllRenderVarsUnset()
@@ -116,6 +118,25 @@ bool debugCheckIntrinsicSizes = false;
 ///    areas are being excessively repainted.
 bool debugProfilePaintsEnabled = false;
 
+/// Signature for [debugOnProfilePaint] implementations.
+typedef ProfilePaintCallback = void Function(RenderObject renderObject);
+
+/// Callback invoked for every [RenderObject] painted each frame.
+///
+/// This callback is only invoked in debug builds.
+///
+/// See also:
+///
+///  * [debugProfilePaintsEnabled], which does something similar but adds
+///    [dart:developer.Timeline] events instead of invoking a callback.
+///  * [debugOnRebuildDirtyWidget], which does something similar for widgets
+///    being built.
+///  * [WidgetInspectorService], which uses the [debugOnProfilePaint]
+///    callback to generate aggregate profile statistics describing what paints
+///    occurred when the `ext.flutter.inspector.trackRepaintWidgets` service
+///    extension is enabled.
+ProfilePaintCallback debugOnProfilePaint;
+
 /// Setting to true will cause all clipping effects from the layer tree to be
 /// ignored.
 ///
@@ -205,7 +226,8 @@ bool debugAssertAllRenderVarsUnset(String reason, { bool debugCheckIntrinsicSize
         debugPrintMarkNeedsPaintStacks ||
         debugPrintLayouts ||
         debugCheckIntrinsicSizes != debugCheckIntrinsicSizesOverride ||
-        debugProfilePaintsEnabled) {
+        debugProfilePaintsEnabled ||
+        debugOnProfilePaint != null) {
       throw FlutterError(reason);
     }
     return true;

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

@@ -161,6 +161,8 @@ class PaintingContext extends ClipContext {
     assert(() {
       if (debugProfilePaintsEnabled)
         Timeline.startSync('${child.runtimeType}', arguments: timelineWhitelistArguments);
+      if (debugOnProfilePaint != null)
+        debugOnProfilePaint(child);
       return true;
     }());
 

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

@@ -711,6 +711,11 @@ mixin WidgetsBinding on BindingBase, SchedulerBinding, GestureBinding, RendererB
 
   @override
   Future<void> performReassemble() {
+    assert(() {
+      WidgetInspectorService.instance.performReassemble();
+      return true;
+    }());
+
     deferFirstFrameReport();
     if (renderViewElement != null)
       buildOwner.reassemble(renderViewElement);

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

@@ -30,6 +30,26 @@ import 'table.dart';
 /// See also the discussion at [WidgetsBinding.drawFrame].
 bool debugPrintRebuildDirtyWidgets = false;
 
+/// Signature for [debugOnRebuildDirtyWidget] implementations.
+typedef RebuildDirtyWidgetCallback = void Function(Element e, bool builtOnce);
+
+/// Callback invoked for every dirty widget built each frame.
+///
+/// This callback is only invoked in debug builds.
+///
+/// See also:
+///
+///  * [debugPrintRebuildDirtyWidgets], which does something similar but logs
+///    to the console instead of invoking a callback.
+///  * [debugOnProfilePaint], which does something similar for [RenderObject]
+///    painting.
+///  * [WidgetInspectorService], which uses the [debugOnRebuildDirtyWidget]
+///    callback to generate aggregate profile statistics describing which widget
+///    rebuilds occurred when the
+///    `ext.flutter.inspector.trackRebuildDirtyWidgets` service extension is
+///    enabled.
+RebuildDirtyWidgetCallback debugOnRebuildDirtyWidget;
+
 /// Log all calls to [BuildOwner.buildScope].
 ///
 /// Combined with [debugPrintScheduleBuildForStacks], this allows you to track

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

@@ -3514,6 +3514,9 @@ abstract class Element extends DiagnosticableTree implements BuildContext {
     if (!_active || !_dirty)
       return;
     assert(() {
+      if (debugOnRebuildDirtyWidget != null) {
+        debugOnRebuildDirtyWidget(this, _debugBuiltOnce);
+      }
       if (debugPrintRebuildDirtyWidgets) {
         if (!_debugBuiltOnce) {
           debugPrint('Building $this');

packages/flutter/test/foundation/service_extensions_test.dart

@@ -528,12 +528,18 @@ void main() {
   });
 
   test('Service extensions - posttest', () async {
-    // See widget_inspector_test.dart for tests of the 15 ext.flutter.inspector
+    // See widget_inspector_test.dart for tests of the ext.flutter.inspector
     // service extensions included in this count.
+    int widgetInspectorExtensionCount = 15;
+    if (WidgetInspectorService.instance.isWidgetCreationTracked()) {
+      // Some inspector extensions are only exposed if widget creation locations
+      // are tracked.
+      widgetInspectorExtensionCount += 2;
+    }
 
     // If you add a service extension... TEST IT! :-)
     // ...then increment this number.
-    expect(binding.extensions.length, 38);
+    expect(binding.extensions.length, 23 + widgetInspectorExtensionCount);
 
     expect(console, isEmpty);
     debugPrint = debugPrintThrottled;