SVG-AAM Implementation: Expose SVGs with no accessible children as image

Currently an SVG root element is treated as a document rather than an
image. Given that most SVGs on the web are for icons rather than complex
documents, this exposure might not make sense. There is an open issue in
the SVG-AAM spec's github suggesting that if an SVG has no accessible
children, it should be exposed as an image rather than as a document.
See w3c/svg-aam#12

AX-Relnotes: Expose SVGs with no accessible children as an image rather
than a document.

Bug: 231654
Change-Id: I1b05d713813ecc9546cd26b602b8f6526b41e861
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3195891
Reviewed-by: Aaron Leventhal <[email protected]>
Reviewed-by: Jochen Eisinger <[email protected]>
Reviewed-by: Nektarios Paisios <[email protected]>
Commit-Queue: Aaron Leventhal <[email protected]>
Cr-Commit-Position: refs/heads/main@{#930670}
NOKEYCHECK=True
GitOrigin-RevId: 2b46499fc2ba3e80f2b1f1e3f7fef64fa6be3c03

blink/renderer/modules/accessibility/ax_object.cc

@@ -1056,7 +1056,7 @@ AccessibleNode* AXObject::GetAccessibleNode() const {
 
 void AXObject::Serialize(ui::AXNodeData* node_data,
                          ui::AXMode accessibility_mode) {
-  node_data->role = RoleValue();
+  node_data->role = ComputeFinalRoleForSerialization();
   node_data->id = AXObjectID();
 
   DCHECK(!IsDetached()) << "Do not serialize detached nodes: "
@@ -1727,6 +1727,22 @@ bool AXObject::IsVirtualObject() const {
   return false;
 }
 
+ax::mojom::blink::Role AXObject::ComputeFinalRoleForSerialization() const {
+  // An SVG with no accessible children should be exposed as an image rather
+  // than a document. See https://github.com/w3c/svg-aam/issues/12.
+  // We do this check here for performance purposes: When
+  // AXLayoutObject::RoleFromLayoutObjectOrNode is called, that node's
+  // accessible children have not been calculated. Rather than force calculation
+  // there, wait until we have the full tree.
+  if (role_ == ax::mojom::blink::Role::kSvgRoot && !UnignoredChildCount())
+    return ax::mojom::blink::Role::kImage;
+
+  // TODO(accessibility): Consider moving the image vs. image map role logic
+  // here. Currently it is implemented in AXPlatformNode subclasses and thus
+  // not available to the InspectorAccessibilityAgent.
+  return role_;
+}
+
 ax::mojom::blink::Role AXObject::RoleValue() const {
   return role_;
 }

blink/renderer/modules/accessibility/ax_object.h

@@ -353,6 +353,14 @@ class MODULES_EXPORT AXObject : public GarbageCollected<AXObject> {
   // Check object role or purpose.
   ax::mojom::blink::Role RoleValue() const;
 
+  // This method is useful in cases where the final role exposed to ATs needs
+  // to change based on contextual information. For instance, an svgRoot should
+  // be exposed as an image if it lacks accessible children. Whether or not it
+  // has accessible children is not known at the time the role is assigned and
+  // may depend on whether or not a given platform includes children that other
+  // platforms ignore.
+  ax::mojom::blink::Role ComputeFinalRoleForSerialization() const;
+
   // Returns true if this object is an ARIA text field, i.e. it is neither an
   // <input> nor a <textarea>, but it has an ARIA role of textbox, searchbox or
   // (on certain platforms) combobox.

blink/renderer/modules/accessibility/inspector_accessibility_agent.cc

@@ -211,7 +211,7 @@ bool RoleAllowsSort(ax::mojom::Role role) {
 
 void FillWidgetProperties(AXObject& ax_object,
                           protocol::Array<AXProperty>& properties) {
-  ax::mojom::Role role = ax_object.RoleValue();
+  ax::mojom::blink::Role role = ax_object.ComputeFinalRoleForSerialization();
   String autocomplete = ax_object.AutoComplete();
   if (!autocomplete.IsEmpty())
     properties.emplace_back(
@@ -303,7 +303,7 @@ void FillWidgetProperties(AXObject& ax_object,
 
 void FillWidgetStates(AXObject& ax_object,
                       protocol::Array<AXProperty>& properties) {
-  ax::mojom::Role role = ax_object.RoleValue();
+  ax::mojom::blink::Role role = ax_object.ComputeFinalRoleForSerialization();
   const char* checked_prop_val = nullptr;
   switch (ax_object.CheckedState()) {
     case ax::mojom::CheckedState::kTrue:
@@ -695,7 +695,7 @@ std::unique_ptr<AXNode> InspectorAccessibilityAgent::BuildProtocolAXObject(
     bool fetch_relatives,
     std::unique_ptr<protocol::Array<AXNode>>& nodes,
     AXObjectCacheImpl& cache) const {
-  ax::mojom::Role role = ax_object.RoleValue();
+  ax::mojom::blink::Role role = ax_object.ComputeFinalRoleForSerialization();
   std::unique_ptr<AXNode> node_object =
       AXNode::create()
           .setNodeId(String::Number(ax_object.AXObjectID()))
@@ -957,7 +957,7 @@ void InspectorAccessibilityAgent::AddChildren(
 namespace {
 
 void setNameAndRole(const AXObject& ax_object, std::unique_ptr<AXNode>& node) {
-  ax::mojom::blink::Role role = ax_object.RoleValue();
+  ax::mojom::blink::Role role = ax_object.ComputeFinalRoleForSerialization();
   node->setRole(CreateRoleNameValue(role));
   AXObject::NameSources name_sources;
   String computed_name = ax_object.GetName(&name_sources);
@@ -1021,7 +1021,8 @@ Response InspectorAccessibilityAgent::queryAXTree(
 
     // if querying by role: skip if role of current object does not match.
     if (role.isJust() &&
-        role.fromJust() != AXObject::RoleName(ax_object->RoleValue())) {
+        role.fromJust() !=
+            AXObject::RoleName(ax_object->ComputeFinalRoleForSerialization())) {
       continue;
     }
 

blink/web_tests/http/tests/inspector-protocol/accessibility/accessibility-ignoredNodes-expected.txt

@@ -16,7 +16,7 @@ RootWebArea
 
 RootWebArea
   img
-    *SvgRoot
+    *img
 {
     childIds : <object>
     domNode : svg
@@ -47,8 +47,8 @@ RootWebArea
     properties : [
     ]
     role : {
-        type : internalRole
-        value : SvgRoot
+        type : role
+        value : img
     }
 }
 

blink/web_tests/http/tests/inspector-protocol/accessibility/accessibility-nameSources-img-figure-expected.txt

@@ -671,8 +671,8 @@ Tests name sources in images and figures.
         }
     ]
     role : {
-        type : internalRole
-        value : SvgRoot
+        type : role
+        value : img
     }
 }