Click-and-dragging in widget selection mode updates the inspected widget in DevTools (#159352)

Fixes flutter/devtools#8539

Author: elliette

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

@@ -2958,6 +2958,9 @@ class _WidgetInspectorState extends State<WidgetInspector>
     final Rect bounds = (Offset.zero & (view.physicalSize / view.devicePixelRatio)).deflate(_kOffScreenMargin);
     if (!bounds.contains(_lastPointerLocation!)) {
       selection.clear();
+    } else {
+      // Otherwise notify DevTools of the current selection.
+      WidgetInspectorService.instance._sendInspectEvent(selection.current);
     }
   }
 

packages/flutter/test/widgets/widget_inspector_test.dart

@@ -414,6 +414,30 @@ class _TestWidgetInspectorService extends TestWidgetInspectorService {
         );
       }
 
+      Future<void> panAndVerifyWidgetSelection({
+        required Finder startAt,
+        required Finder endAt,
+        required bool isSelected,
+        required GlobalKey widgetKey,
+      }) async {
+        // Pan to the widget.
+        final ui.Offset start = tester.getCenter(startAt);
+        final ui.Offset end = tester.getCenter(endAt);
+        await tester.dragFrom(
+          tester.getCenter(startAt),
+          Offset(end.dx - start.dx, end.dy - start.dy),
+        );
+        await tester.pump();
+
+        // Verify the pan end was intercepted by the Widget Inspector.
+        final RenderObject renderObject =
+            find.byKey(widgetKey).evaluate().first.renderObject!;
+        expect(
+          WidgetInspectorService.instance.selection.candidates,
+          contains(renderObject),
+        );
+      }
+
       await tester.pumpWidget(
         Directionality(
           textDirection: TextDirection.ltr,
@@ -475,6 +499,37 @@ class _TestWidgetInspectorService extends TestWidgetInspectorService {
       );
       expect(log, equals(<String>[]));
 
+
+      // Now pan to the top button and verify it's selected in the Inspector.
+      await panAndVerifyWidgetSelection(
+        startAt: find.text('BOTTOM'),
+        endAt: find.text('TOP'),
+        isSelected: true,
+        widgetKey: topButtonKey,
+      );
+      expect(
+        paragraphText(
+          WidgetInspectorService.instance.selection.current! as RenderParagraph,
+        ),
+        equals('TOP'),
+      );
+      expect(log, equals(<String>[]));
+
+      // Now pan to the bottom button and verify it's selected in the Inspector.
+      await panAndVerifyWidgetSelection(
+        startAt: find.text('TOP'),
+        endAt: find.text('BOTTOM'),
+        isSelected: true,
+        widgetKey: bottomButtonKey,
+      );
+      expect(
+        paragraphText(
+          WidgetInspectorService.instance.selection.current! as RenderParagraph,
+        ),
+        equals('BOTTOM'),
+      );
+      expect(log, equals(<String>[]));
+
       // Now exit selection mode by tapping the Exit Selection Mode button.
       await tester.tap(find.byKey(exitWidgetSelectionButtonKey));
       await tester.pump();