EXPERIMENT Make toPositionInFlatTree() to return null for DOM position not in flat tree

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

Index: third_party/WebKit/Source/core/editing/SelectionEditor.cpp
diff --git a/third_party/WebKit/Source/core/editing/SelectionEditor.cpp b/third_party/WebKit/Source/core/editing/SelectionEditor.cpp
index 615c5d770b4043b30b15b649f011dc21ed370af3..ba0b25356aa4229361fdde825b0699768f6103b3 100644
--- a/third_party/WebKit/Source/core/editing/SelectionEditor.cpp
+++ b/third_party/WebKit/Source/core/editing/SelectionEditor.cpp
@@ -377,15 +377,22 @@ void SelectionEditor::updateCachedVisibleSelectionIfNeeded() const {
     m_cachedVisibleSelectionInFlatTree = VisibleSelectionInFlatTree();
     return;
   }
-  m_cachedVisibleSelectionInFlatTree = createVisibleSelection(
-      SelectionInFlatTree::Builder()
-          .setBaseAndExtent(toPositionInFlatTree(m_selection.base()),
-                            toPositionInFlatTree(m_selection.extent()))
-          .setAffinity(m_selection.affinity())
-          .setHasTrailingWhitespace(m_selection.hasTrailingWhitespace())
-          .setGranularity(m_selection.granularity())
-          .setIsDirectional(m_selection.isDirectional())
-          .build());
+  const PositionInFlatTree& base = toPositionInFlatTree(m_selection.base());
+  const PositionInFlatTree& extent = toPositionInFlatTree(m_selection.extent());
+  SelectionInFlatTree::Builder builder;
+  builder.setAffinity(m_selection.affinity())
+      .setHasTrailingWhitespace(m_selection.hasTrailingWhitespace())
+      .setGranularity(m_selection.granularity())
+      .setIsDirectional(m_selection.isDirectional());
+  // TODO(editing-dev): Is it better to adjust base and extent if they are not
+  // in flat tree?
+  if (base.isNotNull() && extent.isNotNull())
+    builder.setBaseAndExtent(base, extent);
+  else if (base.isNotNull())
+    builder.collapse(base);
+  else if (extent.isNotNull())
+    builder.collapse(extent);
+  m_cachedVisibleSelectionInFlatTree = createVisibleSelection(builder.build());

[Xiaocheng, 2017/03/27 18:17:45]

Is it fine if the cached VS and VSInFlatTree have different types (e.g., VS is
range but VSInFlatTree is Caret)?

[yosin_UTC9, 2017/03/29 03:20:21]

So far, we did adjustment in [1] which removed adjustment function. However, it
doesn't handle this case.
We want to have smarter adjustment, e.g. move a position before shadow host,
etc.

Since we're rewriting selection paint adjustment for layout NG, this case should
be handle there.

[1] http://crrrev.com/2706003002: Get rid of unused functions
SelectionAdjuster::adjustSelectionIn{DOM,Flat}Tree

[Xiaocheng, 2017/03/29 23:56:40]

OK. So the type mismatch currently exists, and will be eliminated systematically
later.

In this case, I don't mind introducing one more source of mismatch.

 }
 
 void SelectionEditor::cacheRangeOfDocument(Range* range) {