[editing] Make PositionTemplate::LastPositionInOrAfterNode() not to m…

…ake invalid position

This patch changes `PositionTemplate::LastPositionInOrAfterNode()`
not to call `PositionTemplate::AfterNode()` when specified `Node`
doesn't have parent `Node` which is invalid position.

Bug: 1248760
Change-Id: I5cab0b8a44975d51e32e42308acd717128713258
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3828389
Auto-Submit: Yoshifumi Inoue <yosin@chromium.org>
Commit-Queue: Kent Tamura <tkent@chromium.org>
Reviewed-by: Kent Tamura <tkent@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1034938}

third_party/blink/renderer/core/editing/position.cc

@@ -577,8 +577,9 @@ PositionTemplate<Strategy>::FirstPositionInOrBeforeNode(const Node& node) {
 template <typename Strategy>
 PositionTemplate<Strategy>
 PositionTemplate<Strategy>::LastPositionInOrAfterNode(const Node& node) {
-  return EditingIgnoresContent(node) ? AfterNode(node)
-                                     : LastPositionInNode(node);
+  return EditingIgnoresContent(node) && Strategy::Parent(node)
+             ? AfterNode(node)
+             : LastPositionInNode(node);
 }
 
 PositionInFlatTree ToPositionInFlatTree(const Position& pos) {

third_party/blink/renderer/core/editing/position_test.cc

@@ -72,6 +72,25 @@ TEST_F(PositionTest, editingPositionOfWithEditingIgnoresContent) {
             Position::EditingPositionOf(textarea, 3));
 }
 
+// http://crbug.com/1248760
+TEST_F(PositionTest, LastPositionInOrAfterNodeNotInFlatTree) {
+  SetBodyContent("<option><select>A</select></option>");
+  const Element& document_element = *GetDocument().documentElement();
+  const Element& select = *GetDocument().QuerySelector("select");
+
+  EXPECT_EQ(Position::LastPositionInNode(document_element),
+            Position::LastPositionInOrAfterNode(document_element));
+  EXPECT_EQ(PositionInFlatTree::LastPositionInNode(document_element),
+            PositionInFlatTree::LastPositionInOrAfterNode(document_element));
+
+  // Note: <select> isn't appeared in flat tree, because <option> doesn't
+  // take it as valid child node.
+  EXPECT_EQ(Position::AfterNode(select),
+            Position::LastPositionInOrAfterNode(select));
+  EXPECT_EQ(PositionInFlatTree::LastPositionInNode(select),
+            PositionInFlatTree::LastPositionInOrAfterNode(select));
+}
+
 TEST_F(PositionTest, NodeAsRangeLastNode) {
   const char* body_content =
       "<p id='p1'>11</p><p id='p2'></p><p id='p3'>33</p>";