Bug 1693411: Make sure an a11y node is removed when visibility: hidden is set but the layout frame is reconstructed; e.g. position: fixed. r=eeejay

Differential Revision: https://phabricator.services.mozilla.com/D105934

accessible/generic/DocAccessible.cpp

@@ -1584,6 +1584,18 @@ bool DocAccessible::PruneOrInsertSubtree(nsIContent* aRoot) {
     // We schedule it for reinsertion. For example, a slotted element
     // can change its slot attribute to a different slot.
     insert = true;
+
+    // If the frame is invisible, remove it.
+    // Normally, layout sends explicit a11y notifications for visibility
+    // changes (see SendA11yNotifications in RestyleManager). However, if a
+    // visibility change also reconstructs the frame, we must handle it here.
+    if (frame && !frame->StyleVisibility()->IsVisible()) {
+      ContentRemoved(aRoot);
+      // There might be visible descendants, so we want to walk the subtree.
+      // However, we know we don't want to reinsert this node, so we set insert
+      // to false.
+      insert = false;
+    }
   } else {
     // If there is no current accessible, and the node has a frame, or is
     // display:contents, schedule it for insertion.

accessible/tests/mochitest/treeupdate/test_delayed_removal.html

@@ -341,6 +341,40 @@
       is(getAccessible("c14").name, "one two three", "subtree has correct order");
     }
 
+    // Ensure that a node is removed when visibility: hidden is set but the
+    // layout frame is reconstructed; e.g. because of position: fixed. Also
+    // ensure that visible children aren't clobbered.
+    async function visibilityHiddenWithReframe() {
+      let msg = "visibilityHiddenWithReframe";
+      info(msg);
+
+      testAccessibleTree("c15", { SECTION: [ // c15
+        { SECTION: [ // c15_inner
+          { TEXT_LEAF: [] }, // Text
+          { PARAGRAPH: [
+            { TEXT_LEAF: [] } // Para
+          ] },
+          { HEADING: [ // c15_visible
+            { TEXT_LEAF: [] } // Visible
+          ] }, // c15_visible
+        ] } // c15_inner
+      ] });
+
+      let events = waitForOrderedEvents([
+          [EVENT_HIDE, "c15_inner"],
+          [EVENT_SHOW, "c15_visible"],
+          [EVENT_REORDER, "c15"],
+        ], msg);
+      getNode("c15_inner").style = "visibility: hidden; position: fixed;";
+      await events;
+
+      testAccessibleTree("c15", { SECTION: [ // c15
+        { HEADING: [ // c15_visible
+          { TEXT_LEAF: [] } // Visible
+        ] }, // c15_visible
+      ] });
+    }
+
     async function doTest() {
       await hideDivFromInsideSpan();
 
@@ -369,6 +403,9 @@
       await testCSSGeneratedContentRemovedFromButton();
 
       await testSlack();
+
+      await visibilityHiddenWithReframe();
+
       SimpleTest.finish();
     }
 
@@ -448,6 +485,12 @@
     </div>
   </div>
 
+  <div id="c15"><div id="c15_inner">
+    Text
+    <p>Para</p>
+    <h1 id="c15_visible" style="visibility: visible;">Visible</h1>
+  </div></div>
+
   <div id="eventdump"></div>
 </body>
 </html>