Stop flat tree selection canonicalization from using invalid positions

third_party/WebKit/Source/core/editing/SelectionEditor.cpp

 /*
  * Copyright (C) 2004, 2008, 2009, 2010 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 387 matching lines @@
   // Note: Since we |FrameCaret::updateApperance()| is called from
   // |FrameView::performPostLayoutTasks()|, we check lifecycle against
   // |AfterPerformLayout| instead of |LayoutClean|.
   DCHECK_GE(GetDocument().Lifecycle().GetState(),
             DocumentLifecycle::kAfterPerformLayout);
   AssertSelectionValid();
   if (!NeedsUpdateVisibleSelectionInFlatTree())
     return;
   style_version_for_flat_tree_ = GetDocument().StyleVersion();
   cached_visible_selection_in_flat_tree_is_dirty_ = false;
-  cached_visible_selection_in_flat_tree_ = CreateVisibleSelection(
-      SelectionInFlatTree::Builder()
-          .SetBaseAndExtent(ToPositionInFlatTree(selection_.Base()),
-                            ToPositionInFlatTree(selection_.Extent()))
-          .SetAffinity(selection_.Affinity())
-          .SetHasTrailingWhitespace(selection_.HasTrailingWhitespace())
-          .SetGranularity(selection_.Granularity())
-          .SetIsDirectional(selection_.IsDirectional())
-          .Build());
+  SelectionInFlatTree::Builder builder;
+  const PositionInFlatTree& base = ToPositionInFlatTree(selection_.Base());
+  const PositionInFlatTree& extent = ToPositionInFlatTree(selection_.Extent());
+  if (base.IsNotNull() && extent.IsNotNull())
+    builder.SetBaseAndExtent(base, extent);
+  else if (base.IsNotNull())
+    builder.Collapse(base);
+  else if (extent.IsNotNull())
+    builder.Collapse(extent);
+  builder.SetAffinity(selection_.Affinity())
+      .SetHasTrailingWhitespace(selection_.HasTrailingWhitespace())
+      .SetGranularity(selection_.Granularity())
+      .SetIsDirectional(selection_.IsDirectional());
+  cached_visible_selection_in_flat_tree_ =
+      CreateVisibleSelection(builder.Build());
   if (!cached_visible_selection_in_flat_tree_.IsNone())
     return;
   style_version_for_dom_tree_ = GetDocument().StyleVersion();
   cached_visible_selection_in_dom_tree_is_dirty_ = false;
   cached_visible_selection_in_dom_tree_ = VisibleSelection();
 }
 
 void SelectionEditor::CacheRangeOfDocument(Range* range) {
   cached_range_ = range;
 }
 
 Range* SelectionEditor::DocumentCachedRange() const {
   return cached_range_;
 }
 
 void SelectionEditor::ClearDocumentCachedRange() {
   cached_range_ = nullptr;
 }
 
 DEFINE_TRACE(SelectionEditor) {
   visitor->Trace(frame_);
   visitor->Trace(selection_);
   visitor->Trace(cached_visible_selection_in_dom_tree_);
   visitor->Trace(cached_visible_selection_in_flat_tree_);
   visitor->Trace(cached_range_);
   SynchronousMutationObserver::Trace(visitor);
 }
 
 }  // namespace blink