[editing] Fix DCHECK failure in ToPositionInFlatTree

A Shadow DOM V0 insertion point can't participate in the flat tree, so
attempting to convert a Position with such an anchor node into a
PositionInFlatTree used to produce a DCHECK failure.

This patch makes ToPositionInFlatTree use a position with the parent
node, if the given one is a V0 insertion point.

Bug: 1151536

Test=PositionTest.ToPositionInFlatTreeWithV0InsertionPoint1
Test=PositionTest.ToPositionInFlatTreeWithV0InsertionPoint2
Test=PositionTest.ToPositionInFlatTreeWithV0InsertionPoint3

Change-Id: I2d823294ed092ceb7dca4cd708fd75eca5a55f92
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2551131
Commit-Queue: Oriol Brufau <obrufau@igalia.com>
Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#830527}

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

@@ -592,6 +592,10 @@ PositionInFlatTree ToPositionInFlatTree(const Position& pos) {
   if (pos.IsOffsetInAnchor()) {
     if (anchor->IsCharacterDataNode())
       return PositionInFlatTree(anchor, pos.ComputeOffsetInContainerNode());
+    if (IsActiveV0InsertionPoint(*anchor)) {
+      return ToPositionInFlatTree(Position(NodeTraversal::Parent(*anchor),
+                                           NodeTraversal::Index(*anchor)));
+    }
     DCHECK(!anchor->IsElementNode() || anchor->CanParticipateInFlatTree());
     int offset = pos.ComputeOffsetInContainerNode();
     Node* child = NodeTraversal::ChildAt(*anchor, offset);
@@ -620,9 +624,11 @@ PositionInFlatTree ToPositionInFlatTree(const Position& pos) {
 
   if (anchor->IsShadowRoot())
     return PositionInFlatTree(anchor->OwnerShadowHost(), pos.AnchorType());
+  if (IsActiveV0InsertionPoint(*anchor))
+    return ToPositionInFlatTree(pos.ToOffsetInAnchor());
+  DCHECK(anchor->CanParticipateInFlatTree());
   if (pos.IsBeforeAnchor() || pos.IsAfterAnchor()) {
-    if (anchor->CanParticipateInFlatTree() &&
-        !FlatTreeTraversal::Parent(*anchor)) {
+    if (!FlatTreeTraversal::Parent(*anchor)) {
       // For Before/AfterAnchor, if |anchor| doesn't have parent in the flat
       // tree, there is no valid corresponding PositionInFlatTree.
       // Since this function is a primitive function, we do not adjust |pos|

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

@@ -228,6 +228,62 @@ TEST_F(PositionTest, ToPositionInFlatTreeWithEmptyShadowRoot) {
             ToPositionInFlatTree(Position(shadow_root, 0)));
 }
 
+TEST_F(PositionTest, ToPositionInFlatTreeWithV0InsertionPoint1) {
+  SetBodyContent("<p id=host></p>");
+  ShadowRoot* shadow_root = SetShadowContent("<content></content>", "host");
+  Element* host = GetDocument().getElementById("host");
+  Node* content = shadow_root->QuerySelector("content");
+  EXPECT_FALSE(content->CanParticipateInFlatTree());
+  EXPECT_EQ(PositionInFlatTree(host, 0),
+            ToPositionInFlatTree(Position::BeforeNode(*content)));
+  EXPECT_EQ(PositionInFlatTree(host, 0),
+            ToPositionInFlatTree(Position::FirstPositionInNode(*content)));
+  EXPECT_EQ(PositionInFlatTree(host, 0),
+            ToPositionInFlatTree(Position(content, 0)));
+  EXPECT_EQ(PositionInFlatTree(host, 0),
+            ToPositionInFlatTree(Position::LastPositionInNode(*content)));
+  EXPECT_EQ(PositionInFlatTree::LastPositionInNode(*host),
+            ToPositionInFlatTree(Position::AfterNode(*content)));
+}
+
+TEST_F(PositionTest, ToPositionInFlatTreeWithV0InsertionPoint2) {
+  SetBodyContent("<p id=host></p>");
+  ShadowRoot* shadow_root =
+      SetShadowContent("foo<content></content>bar", "host");
+  Element* host = GetDocument().getElementById("host");
+  Node* content = shadow_root->QuerySelector("content");
+  EXPECT_FALSE(content->CanParticipateInFlatTree());
+  EXPECT_EQ(PositionInFlatTree(host, 1),
+            ToPositionInFlatTree(Position::BeforeNode(*content)));
+  EXPECT_EQ(PositionInFlatTree(host, 1),
+            ToPositionInFlatTree(Position::FirstPositionInNode(*content)));
+  EXPECT_EQ(PositionInFlatTree(host, 1),
+            ToPositionInFlatTree(Position(content, 0)));
+  EXPECT_EQ(PositionInFlatTree(host, 1),
+            ToPositionInFlatTree(Position::LastPositionInNode(*content)));
+  EXPECT_EQ(PositionInFlatTree(host, 1),
+            ToPositionInFlatTree(Position::AfterNode(*content)));
+}
+
+TEST_F(PositionTest, ToPositionInFlatTreeWithV0InsertionPoint3) {
+  SetBodyContent("<p id=host><b>11</b><b>22</b></p>");
+  ShadowRoot* shadow_root =
+      SetShadowContent("foo<content></content>bar", "host");
+  Element* host = GetDocument().getElementById("host");
+  Node* content = shadow_root->QuerySelector("content");
+  EXPECT_FALSE(content->CanParticipateInFlatTree());
+  EXPECT_EQ(PositionInFlatTree(host, 1),
+            ToPositionInFlatTree(Position::BeforeNode(*content)));
+  EXPECT_EQ(PositionInFlatTree(host, 1),
+            ToPositionInFlatTree(Position::FirstPositionInNode(*content)));
+  EXPECT_EQ(PositionInFlatTree(host, 1),
+            ToPositionInFlatTree(Position(content, 0)));
+  EXPECT_EQ(PositionInFlatTree(host, 1),
+            ToPositionInFlatTree(Position::LastPositionInNode(*content)));
+  EXPECT_EQ(PositionInFlatTree(host, 3),
+            ToPositionInFlatTree(Position::AfterNode(*content)));
+}
+
 TEST_F(PositionTest, NullPositionNotConnected) {
   EXPECT_FALSE(Position().IsConnected());
   EXPECT_FALSE(PositionInFlatTree().IsConnected());