Introduce NGInlineCursor::MoveTo{Next,Previous}InlineLeaf{,IgnoringLineBreak}()

This patch introduces member functions to |NGInlineCursor| for preparation of
the patch[1]:
 - MoveToNextInlineLeaf()
 - MoveToNextInlineLeafIgnoringLineBreak()
 - MoveToPreviousInlineLeaf()
 - MoveToPreviousInlineLeafIgnoringLineBreak()
along with helper functions:
 - MoveToPrevious()
  * MoveToPreviousPaintFragment()
  * MoveToPreviousSiblingPaintFragment()
used in |AbstractInlineBox|, |AXInlineTextBox| and |AXLayoutObject|.

Note: These functions are similar to |NGPaintFragmentTraversal|, but these
functions doesn't skip adjacent inline leaf when starting from non-inline
leaf fragment.
 PFT |<b>abc</b><b>def</b> => next =>|<b>abc</b><b>|def</b>
 IC  |<b>abc</b><b>def</b> => next => <b>|abc</b><b>|def</b>

This change affects only |{Next,Previous}OnLineInlineNG()| for |AXLayoutObject|.

[1] http://crrev.com/c/1888242 Utilize NGInlineCursor for inline box traversal

Bug: 982194
Change-Id: I0eac23fde8e4eb1028c98c76c17bc584d4e86bd2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1895258
Commit-Queue: Koji Ishii <kojii@chromium.org>
Reviewed-by: Koji Ishii <kojii@chromium.org>
Auto-Submit: Yoshifumi Inoue <yosin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#712056}

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

@@ -712,6 +712,19 @@ void NGInlineCursor::MoveToNextForSameLayoutObject() {
   }
 }
 
+void NGInlineCursor::MoveToNextInlineLeaf() {
+  if (IsNotNull() && IsInlineLeaf())
+    MoveToNext();
+  while (IsNotNull() && !IsInlineLeaf())
+    MoveToNext();
+}
+
+void NGInlineCursor::MoveToNextInlineLeafIgnoringLineBreak() {
+  do {
+    MoveToNextInlineLeaf();
+  } while (IsNotNull() && IsLineBreak());
+}
+
 void NGInlineCursor::MoveToNextLine() {
   DCHECK(IsLineBox());
   if (current_paint_fragment_) {
@@ -740,6 +753,25 @@ void NGInlineCursor::MoveToNextSkippingChildren() {
   MoveToNextItemSkippingChildren();
 }
 
+void NGInlineCursor::MoveToPrevious() {
+  if (root_paint_fragment_)
+    return MoveToPreviousPaintFragment();
+  MoveToPreviousItem();
+}
+
+void NGInlineCursor::MoveToPreviousInlineLeaf() {
+  if (IsNotNull() && IsInlineLeaf())
+    MoveToPrevious();
+  while (IsNotNull() && !IsInlineLeaf())
+    MoveToPrevious();
+}
+
+void NGInlineCursor::MoveToPreviousInlineLeafIgnoringLineBreak() {
+  do {
+    MoveToPreviousInlineLeaf();
+  } while (IsNotNull() && IsLineBreak());
+}
+
 void NGInlineCursor::MoveToPreviousLine() {
   DCHECK(IsLineBox());
   if (current_paint_fragment_) {
@@ -866,6 +898,30 @@ void NGInlineCursor::MoveToNextPaintFragmentSkippingChildren() {
   }
 }
 
+void NGInlineCursor::MoveToPreviousPaintFragment() {
+  DCHECK(IsPaintFragmentCursor() && current_paint_fragment_);
+  const NGPaintFragment* const parent = current_paint_fragment_->Parent();
+  MoveToPreviousSiblingPaintFragment();
+  if (current_paint_fragment_) {
+    while (TryToMoveToLastChild())
+      continue;
+    return;
+  }
+  current_paint_fragment_ = parent == root_paint_fragment_ ? nullptr : parent;
+}
+
+void NGInlineCursor::MoveToPreviousSiblingPaintFragment() {
+  DCHECK(IsPaintFragmentCursor() && current_paint_fragment_);
+  const NGPaintFragment* const current = current_paint_fragment_;
+  current_paint_fragment_ = nullptr;
+  for (auto* sibling : current->Parent()->Children()) {
+    if (sibling == current)
+      return;
+    current_paint_fragment_ = sibling;
+  }
+  NOTREACHED();
+}
+
 std::ostream& operator<<(std::ostream& ostream, const NGInlineCursor& cursor) {
   if (cursor.IsNull())
     return ostream << "NGInlineCursor()";

third_party/blink/renderer/core/layout/ng/inline/ng_inline_cursor.h

@@ -248,6 +248,15 @@ class CORE_EXPORT NGInlineCursor {
   // Same as |MoveToNext| except that this skips children even if they exist.
   void MoveToNextSkippingChildren();
 
+  // Move the current to next/previous inline leaf.
+  void MoveToNextInlineLeaf();
+  void MoveToNextInlineLeafIgnoringLineBreak();
+  void MoveToPreviousInlineLeaf();
+  void MoveToPreviousInlineLeafIgnoringLineBreak();
+
+  // Move the cursor position to previous fragment in pre-order DFS.
+  void MoveToPrevious();
+
   // Move the current position to previous line. It is error to call other than
   // line box.
   void MoveToPreviousLine();
@@ -299,6 +308,8 @@ class CORE_EXPORT NGInlineCursor {
   void MoveToNextSiblingPaintFragment();
   void MoveToNextPaintFragmentSkippingChildren();
 
+  void MoveToPreviousPaintFragment();
+  void MoveToPreviousSiblingPaintFragment();
   ItemsSpan items_;
   ItemsSpan::iterator item_iter_;
   const NGFragmentItem* current_item_ = nullptr;

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

@@ -288,6 +288,32 @@ TEST_P(NGInlineCursorTest, Next) {
                                 "#span2", "text3", "text4", "text5"));
 }
 
+TEST_P(NGInlineCursorTest, NextInlineLeaf) {
+  // TDOO(yosin): Remove <style> once NGFragmentItem don't do culled inline.
+  InsertStyleElement("b { background: gray; }");
+  NGInlineCursor cursor =
+      SetupCursor("<div id=root>abc<b>DEF</b><br>xyz</div>");
+  Vector<String> list;
+  while (cursor) {
+    list.push_back(ToDebugString(cursor));
+    cursor.MoveToNextInlineLeaf();
+  }
+  EXPECT_THAT(list, ElementsAre("#linebox", "abc", "DEF", "", "xyz"));
+}
+
+TEST_P(NGInlineCursorTest, NextInlineLeafIgnoringLineBreak) {
+  // TDOO(yosin): Remove <style> once NGFragmentItem don't do culled inline.
+  InsertStyleElement("b { background: gray; }");
+  NGInlineCursor cursor =
+      SetupCursor("<div id=root>abc<b>DEF</b><br>xyz</div>");
+  Vector<String> list;
+  while (cursor) {
+    list.push_back(ToDebugString(cursor));
+    cursor.MoveToNextInlineLeafIgnoringLineBreak();
+  }
+  EXPECT_THAT(list, ElementsAre("#linebox", "abc", "DEF", "xyz"));
+}
+
 TEST_P(NGInlineCursorTest, NextLine) {
   NGInlineCursor cursor = SetupCursor("<div id=root>abc<br>xyz</div>");
   NGInlineCursor line1(cursor);
@@ -410,6 +436,73 @@ TEST_P(NGInlineCursorTest, EmptyOutOfFlow) {
   EXPECT_THAT(list, ElementsAre());
 }
 
+TEST_P(NGInlineCursorTest, Previous) {
+  // TDOO(yosin): Remove <style> once NGFragmentItem don't do culled inline.
+  InsertStyleElement("b { background: gray; }");
+  NGInlineCursor cursor =
+      SetupCursor("<div id=root>abc<b>DEF</b><br>xyz</div>");
+  // TDOO(yosin): We'll use |MoveTo(*cursor.GetLayoutBlockFlow()->LastChild())|
+  // once |MoveTo()| works with rootless cursor.
+  while (cursor) {
+    NGInlineCursor next(cursor);
+    next.MoveToNext();
+    if (!next)
+      break;
+    cursor = next;
+  }
+  Vector<String> list;
+  while (cursor) {
+    list.push_back(ToDebugString(cursor));
+    cursor.MoveToPrevious();
+  }
+  EXPECT_THAT(list, ElementsAre("xyz", "#linebox", "", "DEF", "LayoutInline B",
+                                "abc", "#linebox"));
+}
+
+TEST_P(NGInlineCursorTest, PreviousInlineLeaf) {
+  // TDOO(yosin): Remove <style> once NGFragmentItem don't do culled inline.
+  InsertStyleElement("b { background: gray; }");
+  NGInlineCursor cursor =
+      SetupCursor("<div id=root>abc<b>DEF</b><br>xyz</div>");
+  // TDOO(yosin): We'll use |MoveTo(*cursor.GetLayoutBlockFlow()->LastChild())|
+  // once |MoveTo()| works with rootless cursor.
+  while (cursor) {
+    NGInlineCursor next(cursor);
+    next.MoveToNext();
+    if (!next)
+      break;
+    cursor = next;
+  }
+  Vector<String> list;
+  while (cursor) {
+    list.push_back(ToDebugString(cursor));
+    cursor.MoveToPreviousInlineLeaf();
+  }
+  EXPECT_THAT(list, ElementsAre("xyz", "", "DEF", "abc"));
+}
+
+TEST_P(NGInlineCursorTest, PreviousInlineLeafIgnoringLineBreak) {
+  // TDOO(yosin): Remove <style> once NGFragmentItem don't do culled inline.
+  InsertStyleElement("b { background: gray; }");
+  NGInlineCursor cursor =
+      SetupCursor("<div id=root>abc<b>DEF</b><br>xyz</div>");
+  // TDOO(yosin): We'll use |MoveTo(*cursor.GetLayoutBlockFlow()->LastChild())|
+  // once |MoveTo()| works with rootless cursor.
+  while (cursor) {
+    NGInlineCursor next(cursor);
+    next.MoveToNext();
+    if (!next)
+      break;
+    cursor = next;
+  }
+  Vector<String> list;
+  while (cursor) {
+    list.push_back(ToDebugString(cursor));
+    cursor.MoveToPreviousInlineLeafIgnoringLineBreak();
+  }
+  EXPECT_THAT(list, ElementsAre("xyz", "DEF", "abc"));
+}
+
 TEST_P(NGInlineCursorTest, PreviousLine) {
   NGInlineCursor cursor = SetupCursor("<div id=root>abc<br>xyz</div>");
   NGInlineCursor line1(cursor);