fix(trace viewer): clear old highlighted elements upon change (#32917)

When the list of highlighted elements changes over time, we should
update the elements marked as `__playwright_target__` in the snapshot.

A good example is an `expect(locator).toHaveText([...])` where the list
of elements changes from 4 items to 3 after clicking a "Delete" button.

packages/playwright-core/src/server/injected/injectedScript.ts

@@ -65,6 +65,7 @@ export class InjectedScript {
   readonly isUnderTest: boolean;
   private _sdkLanguage: Language;
   private _testIdAttributeNameForStrictErrorAndConsoleCodegen: string = 'data-testid';
+  private _markedElements?: { callId: string, elements: Set<Element> };
   // eslint-disable-next-line no-restricted-globals
   readonly window: Window & typeof globalThis;
   readonly document: Document;
@@ -1081,14 +1082,33 @@ export class InjectedScript {
   }
 
   markTargetElements(markedElements: Set<Element>, callId: string) {
-    const customEvent = new CustomEvent('__playwright_target__', {
+    if (this._markedElements?.callId !== callId)
+      this._markedElements = undefined;
+    const previous = this._markedElements?.elements || new Set();
+
+    const unmarkEvent = new CustomEvent('__playwright_unmark_target__', {
       bubbles: true,
       cancelable: true,
       detail: callId,
       composed: true,
     });
-    for (const element of markedElements)
-      element.dispatchEvent(customEvent);
+    for (const element of previous) {
+      if (!markedElements.has(element))
+        element.dispatchEvent(unmarkEvent);
+    }
+
+    const markEvent = new CustomEvent('__playwright_mark_target__', {
+      bubbles: true,
+      cancelable: true,
+      detail: callId,
+      composed: true,
+    });
+    for (const element of markedElements) {
+      if (!previous.has(element))
+        element.dispatchEvent(markEvent);
+    }
+
+    this._markedElements = { callId, elements: markedElements };
   }
 
   private _setupGlobalListenersRemovalDetection() {

packages/playwright-core/src/server/trace/recorder/snapshotterInjected.ts

@@ -139,12 +139,19 @@ export function frameSnapshotStreamer(snapshotStreamer: string, removeNoScript:
     }
 
     private _refreshListeners() {
-      (document as any).addEventListener('__playwright_target__', (event: CustomEvent) => {
+      (document as any).addEventListener('__playwright_mark_target__', (event: CustomEvent) => {
         if (!event.detail)
           return;
         const callId = event.detail as string;
         (event.composedPath()[0] as any).__playwright_target__ = callId;
       });
+      (document as any).addEventListener('__playwright_unmark_target__', (event: CustomEvent) => {
+        if (!event.detail)
+          return;
+        const callId = event.detail as string;
+        if ((event.composedPath()[0] as any).__playwright_target__ === callId)
+          delete (event.composedPath()[0] as any).__playwright_target__;
+      });
     }
 
     private _interceptNativeMethod(obj: any, method: string, cb: (thisObj: any, result: any) => void) {

tests/library/trace-viewer.spec.ts

@@ -761,7 +761,7 @@ test('should highlight target elements', async ({ page, runAndTrace, browserName
     await page.setContent(`
       <div>t1</div>
       <div>t2</div>
-      <div>t3</div>
+      <div id=div3>t3</div>
       <div>t4</div>
       <div>t5</div>
       <div>t6</div>
@@ -778,6 +778,11 @@ test('should highlight target elements', async ({ page, runAndTrace, browserName
     await page.mouse.move(123, 234);
     await page.getByText(/^t\d$/).click().catch(() => {});
     await expect(page.getByText(/t3|t4/)).toBeVisible().catch(() => {});
+
+    const expectPromise = expect(page.getByText(/t3|t4/)).toHaveText(['t4']);
+    await page.waitForTimeout(1000);
+    await page.evaluate(() => document.querySelector('#div3').textContent = 'changed');
+    await expectPromise;
   });
 
   async function highlightedDivs(frameLocator: FrameLocator) {
@@ -825,6 +830,9 @@ test('should highlight target elements', async ({ page, runAndTrace, browserName
 
   const frameExpectStrictViolation = await traceViewer.snapshotFrame('expect.toBeVisible');
   await expect.poll(() => highlightedDivs(frameExpectStrictViolation)).toEqual(['t3', 't4']);
+
+  const frameUpdatedListOfTargets = await traceViewer.snapshotFrame('expect.toHaveText', 2);
+  await expect.poll(() => highlightedDivs(frameUpdatedListOfTargets)).toEqual(['t4']);
 });
 
 test('should highlight target element in shadow dom', async ({ page, server, runAndTrace }) => {