Bug 1650740 - Don't allow text range retrieval when doc tree is not fully constructed. r=morgan

Differential Revision: https://phabricator.services.mozilla.com/D82410

accessible/mac/GeckoTextMarker.mm

@@ -199,6 +199,7 @@ bool GeckoTextMarkerRange::TextInternal(nsAString& aText, AccessibleOrProxy aCur
   // Find the first link that is at or after the start offset.
   for (int32_t i = 0; i < linkCount; i++) {
     AccessibleOrProxy link = LinkAt(aCurrent, i);
+    MOZ_ASSERT(!link.IsNull());
     linkStartOffset = StartOffset(link);
     if (aStartIntlOffset <= linkStartOffset) {
       next = link;

accessible/mac/MOXTextMarkerDelegate.mm

@@ -60,6 +60,23 @@ static nsDataHashtable<nsUint64HashKey, MOXTextMarkerDelegate*> sDelegates;
 }
 
 - (NSString*)moxStringForTextMarkerRange:(id)textMarkerRange {
+  if (mGeckoDocAccessible.IsAccessible()) {
+    if (!mGeckoDocAccessible.AsAccessible()->AsDoc()->HasLoadState(
+            DocAccessible::eTreeConstructed)) {
+      // If the accessible tree is still being constructed the text tree
+      // is not in a traversable state yet.
+      return @"";
+    }
+  } else {
+    if (mGeckoDocAccessible.AsProxy()->State() & states::STALE) {
+      // In the proxy case we don't have access to load state,
+      // so we need to use the less granular generic STALE state
+      // this state also includes DOM unloaded, which isn't ideal.
+      // Since we really only care if the a11y tree is loaded.
+      return @"";
+    }
+  }
+
   mozilla::a11y::GeckoTextMarkerRange range(mGeckoDocAccessible, textMarkerRange);
   return range.Text();
 }