Cherry-pick 6d76fb1. rdar://115226509

    AX: No accessibility label is exposed for display:contents role="treeitem" elements that have a newline before their child text
    https://bugs.webkit.org/show_bug.cgi?id=261376
    rdar://problem/115226509

    Reviewed by Chris Fleizach.

    This patch fixes two bugs:

      1. No accessibility label is exposed for display:contents role="treeitem" elements that have a newline before their child text

      2. Some display:contents role="treeitem" expose text for other
         elements, resulting in that text being doubly-exposed

    The first was caused by a lack of resilience in AccessibilityNodeObject::firstChild.
    AccessibilityNodeObject::textUnderElement relies on iterating through its accessible children like so:

    for (RefPtr child = firstChild(); child; child = child->nextSibling()) {
       ... compute AX text ...
    }

    However, for elements that AXObjectCache::getOrCreate fails to create an
    object for, we would never iterate because firstChild returned nullptr,
    thus resulting in no AX text being gathered. AccessibilityNodeObject::firstChild
    now detects this, and iterates until it finds the first accessible child.

    The second bug was caused by AccessibilityNodeObject::textUnderElement
    recursively calling and textUnderElement for an element that was not
    it's child. With this patch, we detect this and continue the loop when
    it happens.

    New testcases added to accessibility/display-contents/tree-and-treeitems.html.

    * LayoutTests/accessibility/display-contents/tree-and-treeitems-expected.txt:
    * LayoutTests/accessibility/display-contents/tree-and-treeitems.html:
    * Source/WebCore/accessibility/AXLogger.cpp:
    (WebCore::operator<<):
    * Source/WebCore/accessibility/AccessibilityNodeObject.cpp:
    (WebCore::AccessibilityNodeObject::firstChild const):
    (WebCore::AccessibilityNodeObject::textUnderElement const):
    * Source/WebCore/accessibility/AccessibilityObjectInterface.h:

    Canonical link: https://commits.webkit.org/267839@main
Identifier: 265423.1036@safari-7616-branch

LayoutTests/accessibility/display-contents/tree-and-treeitems-expected.txt

@@ -9,17 +9,31 @@ PASS: treeitem1.isExpanded === true
 PASS: treeitem1.hierarchicalLevel === 0
 PASS: treeitem1.isAttributeSupported('AXValue') === true
 PASS: canSetDisclosing === true
+treeitem1 text:
+	AXTitle:
+	AXDescription: Animals
+	AXHelp:
+
 PASS: treeitem2.role === 'AXRole: AXRow'
 PASS: treeitem2.subrole === 'AXSubrole: AXOutlineRow'
 PASS: treeitem2.isExpanded === false
 PASS: treeitem2.hierarchicalLevel === 1
 PASS: treeitem2.disclosedByRow().isEqual(treeitem1) === true
 PASS: canSetDisclosing === false
+treeitem2 text:
+	AXTitle:
+	AXDescription: Birds
+	AXHelp:
+
 PASS: treeitem3.stringValue === 'AXValue: Birds'
 PASS: canSetDisclosing === false
 PASS: treeitem3.role === 'AXRole: AXRow'
 PASS: treeitem3.subrole === 'AXSubrole: AXOutlineRow'
 PASS: treeitem3.isExpanded === true
+treeitem3 text:
+	AXTitle:
+	AXDescription: Cats
+	AXHelp:
 PASS: treeitem3.isSelected === false
 PASS: treeitem3.isSelected === true
 PASS: selectedRow.isEqual(treeitem3) === true

LayoutTests/accessibility/display-contents/tree-and-treeitems.html

@@ -63,6 +63,7 @@
     output += expect("treeitem1.isAttributeSupported('AXValue')", "true");
     var canSetDisclosing = treeitem1.isAttributeSettable('AXDisclosing');
     output += expect("canSetDisclosing", "true");
+    output += `treeitem1 text:\n${platformTextAlternatives(treeitem1)}\n\n`;
 
     var treeitem2 = treeitem1.disclosedRowAtIndex(0);
     output += expect("treeitem2.role", "'AXRole: AXRow'");
@@ -72,6 +73,7 @@
     output += expect("treeitem2.disclosedByRow().isEqual(treeitem1)", "true");
     canSetDisclosing = treeitem2.isAttributeSettable('AXDisclosing');
     output += expect("canSetDisclosing", "false");
+    output += `treeitem2 text:\n${platformTextAlternatives(treeitem2)}\n\n`;
 
     var treeitem3 = treeitem2.childAtIndex(0);
     output += expect("treeitem3.stringValue", "'AXValue: Birds'");
@@ -83,6 +85,7 @@
     output += expect("treeitem3.role", "'AXRole: AXRow'");
     output += expect("treeitem3.subrole", "'AXSubrole: AXOutlineRow'");
     output += expect("treeitem3.isExpanded", "true");
+    output += `treeitem3 text:\n${platformTextAlternatives(treeitem3)}\n`;
 
     var selectedRow, treeitem4, treeitem5, treeitem6;
     // Test that the row can be selected correctly.

Source/WebCore/accessibility/AXLogger.cpp

@@ -395,6 +395,46 @@ TextStream& operator<<(TextStream& stream, const AccessibilitySearchCriteria& cr
     return stream;
 }
 
+TextStream& operator<<(TextStream& stream, AccessibilityTextSource source)
+{
+    switch (source) {
+    case AccessibilityTextSource::Alternative:
+        stream << "Alternative";
+        break;
+    case AccessibilityTextSource::Children:
+        stream << "Children";
+        break;
+    case AccessibilityTextSource::Summary:
+        stream << "Summary";
+        break;
+    case AccessibilityTextSource::Help:
+        stream << "Help";
+        break;
+    case AccessibilityTextSource::Visible:
+        stream << "Visible";
+        break;
+    case AccessibilityTextSource::TitleTag:
+        stream << "TitleTag";
+        break;
+    case AccessibilityTextSource::Placeholder:
+        stream << "Placeholder";
+        break;
+    case AccessibilityTextSource::LabelByElement:
+        stream << "LabelByElement";
+        break;
+    case AccessibilityTextSource::Title:
+        stream << "Title";
+        break;
+    case AccessibilityTextSource::Subtitle:
+        stream << "Subtitle";
+        break;
+    case AccessibilityTextSource::Action:
+        stream << "Action";
+        break;
+    }
+    return stream;
+}
+
 TextStream& operator<<(TextStream& stream, AccessibilityObjectInclusion inclusion)
 {
     switch (inclusion) {

Source/WebCore/accessibility/AccessibilityNodeObject.cpp

@@ -135,16 +135,20 @@ void AccessibilityNodeObject::updateRole()
 
 AccessibilityObject* AccessibilityNodeObject::firstChild() const
 {
-    if (!node())
+    auto* currentChild = node() ? node()->firstChild() : nullptr;
+    if (!currentChild)
         return nullptr;
-
-    Node* firstChild = node()->firstChild();
 
-    if (!firstChild)
+    auto* cache = axObjectCache();
+    if (!cache)
         return nullptr;
 
-    auto objectCache = axObjectCache();
-    return objectCache ? objectCache->getOrCreate(firstChild) : nullptr;
+    auto* axCurrentChild = cache->getOrCreate(currentChild);
+    while (!axCurrentChild && currentChild) {
+        currentChild = currentChild->nextSibling();
+        axCurrentChild = cache->getOrCreate(currentChild);
+    }
+    return axCurrentChild;
 }
 
 AccessibilityObject* AccessibilityNodeObject::lastChild() const
@@ -2382,10 +2386,17 @@ String AccessibilityNodeObject::textUnderElement(AccessibilityTextUnderElementMo
                 continue;
             }
         }
-
+
+        if (node) {
+            auto* childParentElement = child->node() ? child->node()->parentElement() : nullptr;
+            // Do not take the textUnderElement for a different element (determined by child's element parent not being us). Otherwise we may doubly-expose the same text.
+            if (childParentElement && childParentElement != node && childParentElement->shadowHost() != node)
+                continue;
+        }
+
         String childText = child->textUnderElement(mode);
         if (childText.length())
-            appendNameToStringBuilder(builder, childText);
+            appendNameToStringBuilder(builder, WTFMove(childText));
     }
 
     return builder.toString().trim(deprecatedIsSpaceOrNewline).simplifyWhiteSpace(isHTMLSpaceButNotLineBreak);

Source/WebCore/accessibility/AccessibilityObjectInterface.h

@@ -2019,5 +2019,6 @@ WTF::TextStream& operator<<(WTF::TextStream&, AccessibilitySearchKey);
 WTF::TextStream& operator<<(WTF::TextStream&, const AccessibilitySearchCriteria&);
 WTF::TextStream& operator<<(WTF::TextStream&, AccessibilityObjectInclusion);
 WTF::TextStream& operator<<(WTF::TextStream&, const AXCoreObject&);
+WTF::TextStream& operator<<(WTF::TextStream&, AccessibilityTextSource);
 
 } // namespace WebCore