Bug 1800787 - [devtools] Accessibility picker: Hit test using sub-document/panel Accessible if the target is inside a sub-document/panel. r=ayeddi,devtools-reviewers,nchevobbe

This allows the picker to work correctly inside pop-ups, even if the pop-up contains a sub-document.

Differential Revision: https://phabricator.services.mozilla.com/D187242

devtools/server/actors/accessibility/walker.js

@@ -1099,11 +1099,17 @@ class AccessibleWalkerActor extends Actor {
    */
   _findAndAttachAccessible(event) {
     const target = event.originalTarget || event.target;
-    const docAcc = this.getRawAccessibleFor(this.rootDoc);
     const win = target.ownerGlobal;
+    // This event might be inside a sub-document, so don't use this.rootDoc.
+    const docAcc = this.getRawAccessibleFor(win.document);
     const zoom = this.isXUL ? 1 : getCurrentZoom(win);
     const scale = this.pixelRatio / zoom;
-    const rawAccessible = docAcc.getDeepestChildAtPointInProcess(
+    // If the target is inside a pop-up widget, we need to query the pop-up
+    // Accessible, not the DocAccessible. The DocAccessible can't hit test
+    // inside pop-ups.
+    const popup = win.isChromeWindow ? target.closest("panel") : null;
+    const containerAcc = popup ? this.getRawAccessibleFor(popup) : docAcc;
+    const rawAccessible = containerAcc.getDeepestChildAtPointInProcess(
       event.screenX * scale,
       event.screenY * scale
     );