Changeset 295779 in webkit

Timestamp:

Jun 23, 2022, 9:44:06 AM (2 years ago)

Author:

Tyler Wilcock

Message:

AX: AXIsolatedTree::updateChildren sometimes fails to update isolated subtrees when the given live object is ignored
​https://bugs.webkit.org/show_bug.cgi?id=241735

Reviewed by Andres Gonzalez.

Our current algorithm in AXIsolatedTree::updateChildren is:

1. If the object we got an AXChildrenChanged notification for is in the isolated tree, update its isolated children

2. Otherwise, ascend the ancestry to the nearest in-isolated-tree ancestor, and update the children of that object

This is not always adequate when the object passed to updateChildren
is ignored, as in some cases the ancestor has no children changes
but the subtrees of the ignored object do.

This patch fixes this by also checking the live-children of the ignored
object for any that have unitialized children. If so, we call
AXIsolatedTree::updateChildren on those too.

• Source/WebCore/accessibility/AccessibilityObject.h:

(WebCore::AccessibilityObject::childrenInitialized const):
Move from private to public.

• Source/WebCore/accessibility/isolatedtree/AXIsolatedTree.cpp:

(WebCore::AXIsolatedTree::updateChildren):

Canonical link: ​https://commits.webkit.org/251784@main

Location:

trunk/Source/WebCore/accessibility

Files:

• AccessibilityObject.h (modified) (2 diffs)
• isolatedtree/AXIsolatedTree.cpp (modified) (4 diffs)
• isolatedtree/AXIsolatedTree.h (modified) (1 diff)

trunk/Source/WebCore/accessibility/AccessibilityObject.h

@@ -498 +498 @@
 
     virtual void updateRole() { }
+    bool childrenInitialized() const { return m_childrenInitialized; }
     const AccessibilityChildrenVector& children(bool updateChildrenIfNeeded = true) override;
     virtual void addChildren() { }
@@ -828 +829 @@
     
 protected: // FIXME: Make the data members private.
-    bool childrenInitialized() const { return m_childrenInitialized; }
     AccessibilityChildrenVector m_children;
     mutable bool m_childrenInitialized { false };

trunk/Source/WebCore/accessibility/isolatedtree/AXIsolatedTree.cpp

@@ -210 +210 @@
 }
 
+static bool shouldCreateNodeChange(AXCoreObject& axObject)
+{
+    // We should never create an isolated object from an ignored object or one with an invalid ID.
+    return !axObject.accessibilityIsIgnored() && axObject.objectID().isValid();
+}
+
 std::optional<AXIsolatedTree::NodeChange> AXIsolatedTree::nodeChangeForObject(Ref<AXCoreObject> axObject, AttachWrapper attachWrapper)
 {
     ASSERT(isMainThread());
-
-    // We should never create an isolated object from an ignored object.
-    if (axObject->accessibilityIsIgnored())
+    ASSERT(axObject->objectID().isValid());
+
+    if (!shouldCreateNodeChange(axObject.get()))
         return std::nullopt;
-
-    if (!axObject->objectID().isValid()) {
-        // Either the axObject has an invalid ID or something else went terribly wrong. Don't bother doing anything else.
-        ASSERT_NOT_REACHED();
-        return std::nullopt;
-    }
 
     auto object = AXIsolatedObject::create(axObject, this);
@@ -459 +459 @@
 }
 
-void AXIsolatedTree::updateChildren(AXCoreObject& axObject)
+void AXIsolatedTree::updateChildren(AXCoreObject& axObject, ResolveNodeChanges resolveNodeChanges)
 {
     AXTRACE("AXIsolatedTree::updateChildren"_s);
@@ -490 +490 @@
     }
 
-#ifndef NDEBUG
     if (axAncestor != &axObject) {
         AXLOG(makeString("Original object with ID ", axObject.objectID().loggingString(), " wasn't in the isolated tree, so instead updating the closest in-isolated-tree ancestor:"));
         AXLOG(axAncestor);
-    }
-#endif
+        for (auto& child : axObject.children()) {
+            auto* liveChild = dynamicDowncast<AccessibilityObject>(child.get());
+            if (!liveChild || liveChild->childrenInitialized())
+                continue;
+
+            if (!m_nodeMap.contains(liveChild->objectID())) {
+                if (!shouldCreateNodeChange(*liveChild))
+                    continue;
+
+                // This child should be added to the isolated tree but hasn't been yet.
+                // Add it to the nodemap so the recursive call to updateChildren below properly builds the subtree for this object.
+                auto* parent = liveChild->parentObjectUnignored();
+                m_nodeMap.set(liveChild->objectID(), ParentChildrenIDs { parent ? parent->objectID() : AXID(), liveChild->childrenIDs() });
+                m_unresolvedPendingAppends.set(liveChild->objectID(), AttachWrapper::OnMainThread);
+            }
+
+            AXLOG(makeString(
+                "Child ID ", liveChild->objectID().loggingString(), " of original object ID ", axObject.objectID().loggingString(), " was found in the isolated tree with uninitialized live children. Updating its isolated children."
+            ));
+            // Don't immediately resolve node changes in these recursive calls to updateChildren. This avoids duplicate node change creation in this scenario:
+            //   1. Some subtree is updated in the below call to updateChildren.
+            //   2. Later in this function, when updating axAncestor, we update some higher subtree that includes the updated subtree from step 1.
+            updateChildren(*liveChild, ResolveNodeChanges::No);
+        }
+    }
 
     auto oldIDs = m_nodeMap.get(axAncestor->objectID());
@@ -529 +551 @@
             removeSubtreeFromNodeMap(axID, axAncestor);
     }
-    queueRemovalsAndUnresolvedChanges(oldChildrenIDs);
+
+    if (resolveNodeChanges == ResolveNodeChanges::Yes)
+        queueRemovalsAndUnresolvedChanges(oldChildrenIDs);
+    else
+        queueRemovals(oldChildrenIDs);
 
     // Also queue updates to the target node itself and any properties that depend on children().

trunk/Source/WebCore/accessibility/isolatedtree/AXIsolatedTree.h

@@ -347 +347 @@
     void generateSubtree(AXCoreObject&);
     void updateNode(AXCoreObject&);
-    void updateChildren(AXCoreObject&);
+    enum class ResolveNodeChanges : bool { No, Yes };
+    void updateChildren(AXCoreObject&, ResolveNodeChanges = ResolveNodeChanges::Yes);
     void updateNodeProperty(AXCoreObject&, AXPropertyName);
     void updateNodeAndDependentProperties(AXCoreObject&);