fix(role): accessibleName computation should walk the flat dom tree (#19301)

- When visiting `<slot>` element, descend into assigned nodes.
- When node has `assignedSlot`, skip it during regular traversal.

Fixes #18989.

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

@@ -579,7 +579,9 @@ function getElementAccessibleNameInternal(element: Element, options: AccessibleN
   if (allowsNameFromContent || options.embeddedInLabelledBy !== 'none' || options.embeddedInLabel !== 'none' || options.embeddedInTextAlternativeElement || options.embeddedInTargetElement === 'descendant') {
     options.visitedElements.add(element);
     const tokens: string[] = [];
-    const visit = (node: Node) => {
+    const visit = (node: Node, skipSlotted: boolean) => {
+      if (skipSlotted && (node as Element | Text).assignedSlot)
+        return;
       if (node.nodeType === 1 /* Node.ELEMENT_NODE */) {
         const display = getComputedStyle(node as Element)?.getPropertyValue('display') || 'inline';
         let token = getElementAccessibleNameInternal(node as Element, childOptions);
@@ -596,14 +598,20 @@ function getElementAccessibleNameInternal(element: Element, options: AccessibleN
       }
     };
     tokens.push(getPseudoContent(getComputedStyle(element, '::before')));
-    for (let child = element.firstChild; child; child = child.nextSibling)
+    const assignedNodes = element.nodeName === 'SLOT' ? (element as HTMLSlotElement).assignedNodes() : [];
-      visit(child);
+    if (assignedNodes.length) {
-    if (element.shadowRoot) {
+      for (const child of assignedNodes)
-      for (let child = element.shadowRoot.firstChild; child; child = child.nextSibling)
+        visit(child, false);
-        visit(child);
+    } else {
+      for (let child = element.firstChild; child; child = child.nextSibling)
+        visit(child, true);
+      if (element.shadowRoot) {
+        for (let child = element.shadowRoot.firstChild; child; child = child.nextSibling)
+          visit(child, true);
+      }
+      for (const owned of getIdRefs(element, element.getAttribute('aria-owns')))
+        visit(owned, true);
     }
-    for (const owned of getIdRefs(element, element.getAttribute('aria-owns')))
-      visit(owned);
     tokens.push(getPseudoContent(getComputedStyle(element, '::after')));
     const accessibleName = tokens.join('');
     if (accessibleName.trim())

tests/page/selectors-role.spec.ts

@@ -423,3 +423,63 @@ test('errors', async ({ page }) => {
   const e8 = await page.$('role=treeitem[expanded="none"]').catch(e => e);
   expect(e8.message).toContain(`"expanded" must be one of true, false`);
 });
+
+test('should detect accessible name with slots', async ({ page }) => {
+  // Text "foo" is assigned to the slot, should not be used twice.
+  await page.setContent(`
+    <button><div>foo</div></button>
+    <script>
+      (() => {
+        const container = document.querySelector('div');
+        const shadow = container.attachShadow({ mode: 'open' });
+        const slot = document.createElement('slot');
+        shadow.appendChild(slot);
+      })();
+    </script>
+  `);
+  expect(await page.locator(`role=button[name="foo"]`).evaluateAll(els => els.map(e => e.outerHTML))).toEqual([
+    `<button><div>foo</div></button>`,
+  ]);
+
+  // Text "foo" is assigned to the slot, should be used instead of slot content.
+  await page.setContent(`
+    <div>foo</div>
+    <script>
+      (() => {
+        const container = document.querySelector('div');
+        const shadow = container.attachShadow({ mode: 'open' });
+        const button = document.createElement('button');
+        shadow.appendChild(button);
+        const slot = document.createElement('slot');
+        button.appendChild(slot);
+        const span = document.createElement('span');
+        span.textContent = 'pre';
+        slot.appendChild(span);
+      })();
+    </script>
+  `);
+  expect(await page.locator(`role=button[name="foo"]`).evaluateAll(els => els.map(e => e.outerHTML))).toEqual([
+    `<button><slot><span>pre</span></slot></button>`,
+  ]);
+
+  // Nothing is assigned to the slot, should use slot content.
+  await page.setContent(`
+    <div></div>
+    <script>
+      (() => {
+        const container = document.querySelector('div');
+        const shadow = container.attachShadow({ mode: 'open' });
+        const button = document.createElement('button');
+        shadow.appendChild(button);
+        const slot = document.createElement('slot');
+        button.appendChild(slot);
+        const span = document.createElement('span');
+        span.textContent = 'pre';
+        slot.appendChild(span);
+      })();
+    </script>
+  `);
+  expect(await page.locator(`role=button[name="pre"]`).evaluateAll(els => els.map(e => e.outerHTML))).toEqual([
+    `<button><slot><span>pre</span></slot></button>`,
+  ]);
+});