Bug 493683 part 2: When an Accessible mutates, fire name change events on an Accessible labelled by it (or an ancestor thereof) via a relation. r=eeejay

HasNameDependent is now set on an Accessible (and thus its descendants) which has A LABEL_FOR relation.
When text mutations occur on such an Accessible, EventQueue::PushNameChange now queues a name change for the Accessible being labelled.

Differential Revision: https://phabricator.services.mozilla.com/D102677

accessible/base/EventQueue.cpp

@@ -14,6 +14,7 @@
 #ifdef A11Y_LOG
 #  include "Logging.h"
 #endif
+#include "Relation.h"
 
 namespace mozilla {
 namespace a11y {
@@ -48,31 +49,41 @@ bool EventQueue::PushEvent(AccEvent* aEvent) {
 }
 
 bool EventQueue::PushNameChange(Accessible* aTarget) {
-  // Fire name change event on parent given that this event hasn't been
-  // coalesced, the parent's name was calculated from its subtree, and the
-  // subtree was changed.
+  // Fire name change event on parent or related Accessible being labelled given
+  // that this event hasn't been coalesced, the dependent's name was calculated
+  // from this subtree, and the subtree was changed.
+  bool pushed = false;
+  bool checkAncestor = true;
   if (aTarget->HasNameDependent()) {
     // Only continue traversing up the tree if it's possible that the parent
-    // accessible's name can depend on this accessible's name.
+    // Accessible's name (or an Accessible being labelled by this Accessible or
+    // an ancestor) can depend on this Accessible's name.
     Accessible* parent = aTarget->Parent();
     while (parent &&
            nsTextEquivUtils::HasNameRule(parent, eNameFromSubtreeIfReqRule)) {
       // Test possible name dependent parent.
-      if (nsTextEquivUtils::HasNameRule(parent, eNameFromSubtreeRule)) {
+      if (checkAncestor &&
+          nsTextEquivUtils::HasNameRule(parent, eNameFromSubtreeRule)) {
         nsAutoString name;
         ENameValueFlag nameFlag = parent->Name(name);
         // If name is obtained from subtree, fire name change event.
         if (nameFlag == eNameFromSubtree) {
           RefPtr<AccEvent> nameChangeEvent =
               new AccEvent(nsIAccessibleEvent::EVENT_NAME_CHANGE, parent);
-          return PushEvent(nameChangeEvent);
+          pushed |= PushEvent(nameChangeEvent);
         }
-        break;
+        checkAncestor = false;
+      }
+      Relation rel = parent->RelationByType(RelationType::LABEL_FOR);
+      while (Accessible* relTarget = rel.Next()) {
+        RefPtr<AccEvent> nameChangeEvent =
+            new AccEvent(nsIAccessibleEvent::EVENT_NAME_CHANGE, relTarget);
+        pushed |= PushEvent(nameChangeEvent);
       }
       parent = parent->Parent();
     }
   }
-  return false;
+  return pushed;
 }
 
 ////////////////////////////////////////////////////////////////////////////////

accessible/base/NotificationController.h

@@ -114,9 +114,8 @@ class NotificationController final : public EventQueue,
   }
 
   /**
-   * Creates and adds a name change event into the queue for a container of
-   * the given accessible, if the accessible is a part of name computation of
-   * the container.
+   * Creates and adds a name change event into the queue for an Accessible which
+   * depends on the given Accessible for name computation, if any.
    */
   void QueueNameChange(Accessible* aChangeTarget) {
     if (PushNameChange(aChangeTarget)) {

accessible/generic/Accessible.cpp

@@ -2069,8 +2069,8 @@ void Accessible::BindToParent(Accessible* aParent, uint32_t aIndexInParent) {
   mParent = aParent;
   mIndexInParent = aIndexInParent;
 
-  // Note: this is currently only used for richlistitems and their children.
-  if (mParent->HasNameDependent() || mParent->IsXULListItem()) {
+  if (mParent->HasNameDependent() || mParent->IsXULListItem() ||
+      RelationByType(RelationType::LABEL_FOR).Next()) {
     mContextFlags |= eHasNameDependent;
   } else {
     mContextFlags &= ~eHasNameDependent;

accessible/tests/mochitest/events/test_namechange.html

@@ -19,6 +19,11 @@
           src="../states.js"></script>
 
   <script type="application/javascript">
+    let PromEvents = {};
+    Services.scriptloader.loadSubScript(
+      "chrome://mochitests/content/a11y/accessible/tests/mochitest/promisified-events.js",
+      PromEvents);
+
     // //////////////////////////////////////////////////////////////////////////
     // Invokers
 
@@ -57,8 +62,15 @@
     // gA11yEventDumpToConsole = true; // debuggin
 
     var gQueue = null;
-    function doTests() {
+    async function doTests() {
       gQueue = new eventQueue();
+      // Later tests use await.
+      let queueFinished = new Promise(resolve => {
+        gQueue.onFinish = function() {
+          resolve();
+          return DO_NOT_FINISH_TEST;
+        };
+      });
 
       gQueue.push(new setAttr("tst1", "aria-label", "hi",
                               new invokerChecker(EVENT_NAME_CHANGE, "tst1")));
@@ -88,7 +100,26 @@
       gQueue.push(new setAttr("tst4", "title", "title",
                               new invokerChecker(EVENT_NAME_CHANGE, "tst4")));
 
-      gQueue.invoke(); // Will call SimpleTest.finish();
+      gQueue.invoke();
+      await queueFinished;
+      // Tests beyond this point use await rather than eventQueue.
+
+      const labelledBy = getNode("labelledBy");
+      const label = getNode("label");
+      let nameChanged = PromEvents.waitForEvent(EVENT_NAME_CHANGE, labelledBy);
+      info("Changing text of aria-labelledby target");
+      label.textContent = "l2";
+      await nameChanged;
+      nameChanged = PromEvents.waitForEvent(EVENT_NAME_CHANGE, labelledBy);
+      info("Adding node to aria-labelledby target");
+      label.innerHTML = '<p id="labelChild">l3</p>';
+      await nameChanged;
+      nameChanged = PromEvents.waitForEvent(EVENT_NAME_CHANGE, labelledBy);
+      info("Changing text of aria-labelledby target's child");
+      getNode("labelChild").textContent = "l4";
+      await nameChanged;
+
+      SimpleTest.finish();
     }
 
     SimpleTest.waitForExplicitFinish();
@@ -114,6 +145,9 @@
   <img id="tst3">
   <img id="tst4" src="../moz.png">
 
+  <div id="labelledBy" aria-labelledby="label"></div>
+  <div id="label">l1</div>
+
   <div id="eventdump"></div>
 </body>
 </html>