AX: AccessibilityRenderObject::computeAccessibilityIsIgnored performs…

… an unnecessary ancestry traversal for RenderTexts

https://bugs.webkit.org/show_bug.cgi?id=264861
rdar://problem/118437052

Reviewed by Chris Fleizach and Andres Gonzalez.

AccessibilityRenderObject::computeAccessibilityIsIgnored for RenderTexts traverses the ancestry twice.
We can combine this into one traversal. Also modernizes some nearby code to use dynamicDowncast instead
of is + downcast.

* Source/WebCore/accessibility/AccessibilityRenderObject.cpp:
(WebCore::AccessibilityRenderObject::computeAccessibilityIsIgnored const):

Canonical link: https://commits.webkit.org/270805@main

Source/WebCore/accessibility/AccessibilityRenderObject.cpp

@@ -1101,45 +1101,40 @@ bool AccessibilityRenderObject::computeAccessibilityIsIgnored() const
     if (m_renderer->isBR())
         return true;
 
-    if (is<RenderText>(*m_renderer)) {
-        // static text beneath MenuItems and MenuButtons are just reported along with the menu item, so it's ignored on an individual level
-        AXCoreObject* parent = parentObjectUnignored();
-
-        // Walking up the parent chain might reset the m_renderer.
-        if (!m_renderer)
-            return true;
-
-        if (parent && (parent->isMenuItem() || parent->isMenuButton()))
+    if (WeakPtr renderText = dynamicDowncast<RenderText>(m_renderer.get())) {
+        // Text elements with no rendered text, or only whitespace should not be part of the AX tree.
+        if (!renderText->hasRenderedText() || renderText->text().containsOnly<isASCIIWhitespace>())
             return true;
 
-        auto& renderText = downcast<RenderText>(*m_renderer);
-        if (!renderText.hasRenderedText())
+        if (renderText->parent()->isFirstLetter())
             return true;
 
-        if (renderText.parent()->isFirstLetter())
-            return true;
-
-        // static text beneath TextControls is reported along with the text control text so it's ignored.
-        for (AccessibilityObject* parent = parentObject(); parent; parent = parent->parentObject()) { 
-            if (parent->roleValue() == AccessibilityRole::TextField)
-                return true;
-        }
-
-        // Walking up the parent chain might reset the m_renderer.
-        if (!m_renderer)
-            return true;
-
         // The alt attribute may be set on a text fragment through CSS, which should be honored.
-        if (is<RenderTextFragment>(renderText)) {
-            AccessibilityObjectInclusion altTextInclusion = objectInclusionFromAltText(downcast<RenderTextFragment>(renderText).altText());
+        if (auto* renderTextFragment = dynamicDowncast<RenderTextFragment>(renderText.get())) {
+            auto altTextInclusion = objectInclusionFromAltText(renderTextFragment->altText());
             if (altTextInclusion == AccessibilityObjectInclusion::IgnoreObject)
                 return true;
             if (altTextInclusion == AccessibilityObjectInclusion::IncludeObject)
                 return false;
         }
 
-        // text elements that are just empty whitespace should not be returned
-        return renderText.text().containsOnly<isASCIIWhitespace>();
+        bool checkForIgnored = true;
+        for (RefPtr ancestor = parentObject(); ancestor; ancestor = ancestor->parentObject()) {
+            // Static text beneath TextControls is reported along with the text control text so it's ignored.
+            // FIXME: Why does this not check for the other text-control roles (e.g. textarea)?
+            if (ancestor->roleValue() == AccessibilityRole::TextField)
+                return true;
+
+            if (checkForIgnored && !ancestor->accessibilityIsIgnored()) {
+                checkForIgnored = false;
+                // Static text beneath MenuItems and MenuButtons are just reported along with the menu item, so it's ignored on an individual level.
+                if (ancestor->isMenuItem() || ancestor->isMenuButton())
+                    return true;
+            }
+        }
+
+        // If iterating the ancestry has caused m_renderer to be destroyed, ignore `this`.
+        return !renderText;
     }
 
     if (isHeading())