[LayoutNG] Fix coordinate space of NG LocalCaretRect() in vertical-rl

LocalCaretRect should use the "flipped blocks" coordinate space for
vertical-rl writing mode. This patch applies that in the NG implementation.

Note: this patch only changes behavior for text-anchored carets. When
caret is anchored to atomic inline, there is no reference as the legacy
behavior is broken, and LocalCaretRect is consumed by legacy.

Bug: 822575
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_layout_tests_layout_ng
Change-Id: I4019f560f8410ef14c7d52312d7fc1de8db6ee28
Reviewed-on: https://chromium-review.googlesource.com/1011296Reviewed-by: Koji Ishii <kojii@chromium.org>
Commit-Queue: Xiaocheng Hu <xiaochengh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#551528}

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

@@ -201,8 +201,7 @@ TEST_P(ParameterizedLocalCaretRectTest, UnderflowTextRtl) {
                 Position(text, 2), TextAffinity::kDownstream)));
 }
 
-// TODO(xiaochengh): Fix NG LocalCaretText computation for vertical text.
-TEST_F(LocalCaretRectTest, VerticalRLText) {
+TEST_P(ParameterizedLocalCaretRectTest, VerticalRLText) {
   // This test only records the current behavior. Future changes are allowed.
 
   LoadAhem();
@@ -211,11 +210,6 @@ TEST_F(LocalCaretRectTest, VerticalRLText) {
       "font: 10px/10px Ahem; width: 30px; height: 30px'>XXXYYYZZZ</div>");
   const Node* foo = GetElementById("div")->firstChild();
 
-  // TODO(xiaochengh): In vertical-rl writing mode, the |X| property of
-  // LocalCaretRect's LayoutRect seems to refer to the distance to the right
-  // edge of the inline formatting context instead. Figure out if this is
-  // correct.
-
   EXPECT_EQ(LocalCaretRect(foo->GetLayoutObject(), LayoutRect(0, 0, 10, 1)),
             LocalCaretRectOfPosition(PositionWithAffinity(
                 Position(foo, 0), TextAffinity::kDownstream)));

third_party/blink/renderer/core/layout/ng/inline/ng_caret_rect.cc

@@ -7,7 +7,7 @@
 #include "third_party/blink/renderer/core/editing/local_caret_rect.h"
 #include "third_party/blink/renderer/core/editing/position_with_affinity.h"
 #include "third_party/blink/renderer/core/frame/local_frame_view.h"
-#include "third_party/blink/renderer/core/layout/layout_object.h"
+#include "third_party/blink/renderer/core/layout/layout_block_flow.h"
 #include "third_party/blink/renderer/core/layout/ng/geometry/ng_physical_offset_rect.h"
 #include "third_party/blink/renderer/core/layout/ng/inline/ng_caret_position.h"
 #include "third_party/blink/renderer/core/layout/ng/inline/ng_physical_text_fragment.h"
@@ -120,29 +120,38 @@ LocalCaretRect ComputeLocalCaretRect(const NGCaretPosition& caret_position) {
   if (caret_position.IsNull())
     return LocalCaretRect();
 
+  const NGPaintFragment& fragment = *caret_position.fragment;
+  const LayoutObject* layout_object = fragment.GetLayoutObject();
   switch (caret_position.position_type) {
     case NGCaretPositionType::kBeforeBox:
     case NGCaretPositionType::kAfterBox: {
-      DCHECK(caret_position.fragment->PhysicalFragment().IsBox());
+      DCHECK(fragment.PhysicalFragment().IsBox());
       const NGPhysicalOffsetRect fragment_local_rect =
-          ComputeLocalCaretRectByBoxSide(*caret_position.fragment,
+          ComputeLocalCaretRectByBoxSide(fragment,
                                          caret_position.position_type);
-      return {caret_position.fragment->GetLayoutObject(),
-              fragment_local_rect.ToLayoutRect()};
+      return {layout_object, fragment_local_rect.ToLayoutRect()};
     }
     case NGCaretPositionType::kAtTextOffset: {
-      DCHECK(caret_position.fragment->PhysicalFragment().IsText());
+      DCHECK(fragment.PhysicalFragment().IsText());
       DCHECK(caret_position.text_offset.has_value());
       const NGPhysicalOffsetRect caret_rect = ComputeLocalCaretRectAtTextOffset(
-          *caret_position.fragment, *caret_position.text_offset);
-
-      return {caret_position.fragment->GetLayoutObject(),
-              caret_rect.ToLayoutRect()};
+          fragment, *caret_position.text_offset);
+      LayoutRect layout_rect = caret_rect.ToLayoutRect();
+
+      // For vertical-rl, convert to "flipped block-flow" coordinates space.
+      // See core/layout/README.md#coordinate-spaces for details.
+      if (fragment.Style().IsFlippedBlocksWritingMode()) {
+        const LayoutBlockFlow* container =
+            layout_object->EnclosingNGBlockFlow();
+        container->FlipForWritingMode(layout_rect);
+      }
+
+      return {layout_object, layout_rect};
     }
   }
 
   NOTREACHED();
-  return {caret_position.fragment->GetLayoutObject(), LayoutRect()};
+  return {layout_object, LayoutRect()};
 }
 
 }  // namespace