Make PreviousWordPosition() utilitize TextSegments class

This patch changes |PreviousWordPosition()| to utilize |TextSegments|
class to make |PreviousWordPosition()| work with LayoutNG.

This patch also reveals an existing bug (or feature?) in editing
boundary adjustments, as shown in the changed layout test.

Bug: 778507, 900060
Change-Id: Ic797c960715576dc85a946a7b34b0be568c19805
Reviewed-on: https://chromium-review.googlesource.com/c/1307056Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
Commit-Queue: Xiaocheng Hu <xiaochengh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#604152}

third_party/WebKit/LayoutTests/TestExpectations

@@ -4651,6 +4651,9 @@ crbug.com/770232 [ Win10 ] fast/text/unicode-fallback-font.html [ Failure ]
 crbug.com/764489 editing/execCommand/format-block-multiple-paragraphs.html [ Failure ]
 crbug.com/764489 editing/execCommand/format-block-multiple-paragraphs-in-pre.html [ Failure ]
 
+# Previous/NextWordPosition crossing editing boundaries.
+crbug.com/900060 editing/selection/mixed-editability-8.html [ Failure ]
+
 # Sheriff failures 2017-09-11
 crbug.com/763975 [ Linux Mac Debug ] webaudio/internals/cycle-connection-gc.html [ Pass Failure ]
 

third_party/WebKit/LayoutTests/editing/selection/mixed-editability-8.html

@@ -60,5 +60,33 @@ selection_test(
       'editable',
     '</div>',
   ],
-  'Move backward backward');
+  'Move backward word');
+
+selection_test(
+  [
+    '<div contenteditable>',
+      'editable',
+      '<table border="1" contenteditable="false"><tbody><tr><td>',
+        '<div style="display:inline-block;">',
+          '<span contenteditable="plaintext-only">e|ditable</span>',
+          '<span>static</span>',
+         '</div>',
+      '</td></tr></tbody></table>',
+      'editable',
+    '</div>',
+  ],
+  selection => selection.modify('move', 'forward', 'word'),
+  [
+    '<div contenteditable>',
+      'editable',
+      '<table border="1" contenteditable="false"><tbody><tr><td>',
+        '<div style="display:inline-block;">',
+          '<span contenteditable="plaintext-only">editable|</span>',
+          '<span>static</span>',
+         '</div>',
+      '</td></tr></tbody></table>',
+      'editable',
+    '</div>',
+  ],
+  'Move forward word');
 </script>

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

@@ -56,4 +56,28 @@ PositionInFlatTree TextSegments::FindBoundaryForward(
   return last_position;
 }
 
+// static
+PositionInFlatTree TextSegments::FindBoundaryBackward(
+    const PositionInFlatTree& position,
+    Finder* finder) {
+  DCHECK(position.IsNotNull());
+  PositionInFlatTree last_position = position;
+  for (const auto& inline_contents :
+       TextOffsetMapping::BackwardRangeOf(position)) {
+    const TextOffsetMapping mapping(inline_contents);
+    const String text = mapping.GetText();
+    const unsigned offset = last_position == position
+                                ? mapping.ComputeTextOffset(position)
+                                : mapping.GetText().length();
+    const TextSegments::Finder::Position result = finder->Find(text, offset);
+    if (result.IsBefore())
+      return mapping.GetPositionBefore(result.Offset());
+    if (result.IsAfter())
+      return mapping.GetPositionAfter(result.Offset());
+    DCHECK(result.IsNone());
+    last_position = mapping.GetRange().StartPosition();
+  }
+  return last_position;
+}
+
 }  // namespace blink

third_party/blink/renderer/core/editing/text_segments.h

@@ -51,13 +51,15 @@ class TextSegments final {
     virtual Position Find(const String text, unsigned offset) = 0;
   };
 
-  // TODO(editing-dev): We should have |FindBoundaryBackward()|.
-
   // Returns a boundary position found by |finder| followed by |position|
   // (inclusive). |finder| can be stateful or stateless.
   static PositionInFlatTree FindBoundaryForward(
       const PositionInFlatTree& position,
       Finder* finder);
+
+  static PositionInFlatTree FindBoundaryBackward(
+      const PositionInFlatTree& position,
+      Finder* finder);
 };
 
 }  // namespace blink

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

@@ -110,19 +110,30 @@ PositionInFlatTree NextWordPositionInternal(
   return TextSegments::FindBoundaryForward(position, &finder);
 }
 
-unsigned PreviousWordPositionBoundary(
-    const UChar* characters,
-    unsigned length,
-    unsigned offset,
-    BoundarySearchContextAvailability may_have_more_context,
-    bool& need_more_context) {
-  if (may_have_more_context &&
-      !StartOfLastWordBoundaryContext(characters, offset)) {
-    need_more_context = true;
-    return 0;
-  }
-  need_more_context = false;
-  return FindNextWordBackward(characters, length, offset);
+PositionInFlatTree PreviousWordPositionInternal(
+    const PositionInFlatTree& position) {
+  class Finder final : public TextSegments::Finder {
+    STACK_ALLOCATED();
+
+   private:
+    Position Find(const String text, unsigned offset) final {
+      DCHECK_LE(offset, text.length());
+      if (!offset || text.length() == 0)
+        return Position();
+      TextBreakIterator* it =
+          WordBreakIterator(text.Characters16(), text.length());
+      for (int runner = it->preceding(offset); runner != kTextBreakDone;
+           runner = it->preceding(runner)) {
+        // We stop searching when the character following the break is
+        // alphanumeric or underscore.
+        if (runner && (WTF::Unicode::IsAlphanumeric(text[runner]) ||
+                       text[runner] == kLowLineCharacter))
+          return Position::Before(runner);
+      }
+      return Position::Before(0);
+    }
+  } finder;
+  return TextSegments::FindBoundaryBackward(position, &finder);
 }
 
 unsigned StartWordBoundary(
@@ -219,12 +230,24 @@ VisiblePosition NextWordPosition(const VisiblePosition& c) {
   return CreateVisiblePosition(NextWordPosition(c.DeepEquivalent()));
 }
 
+PositionInFlatTreeWithAffinity PreviousWordPosition(
+    const PositionInFlatTree& start) {
+  const PositionInFlatTree prev = PreviousWordPositionInternal(start);
+  return AdjustBackwardPositionToAvoidCrossingEditingBoundaries(
+      PositionInFlatTreeWithAffinity(prev), start);
+}
+
+PositionWithAffinity PreviousWordPosition(const Position& start) {
+  const PositionInFlatTreeWithAffinity& prev =
+      PreviousWordPosition(ToPositionInFlatTree(start));
+  return ToPositionInDOMTreeWithAffinity(prev);
+}
+
+// TODO(xiaochengh): Remove this function. Change callers to use the
+// Position version as it doesn't need canonical input position.
 VisiblePosition PreviousWordPosition(const VisiblePosition& c) {
   DCHECK(c.IsValid()) << c;
-  VisiblePosition prev =
-      CreateVisiblePosition(PreviousBoundary(c, PreviousWordPositionBoundary));
-  return AdjustBackwardPositionToAvoidCrossingEditingBoundaries(
-      prev, c.DeepEquivalent());
+  return CreateVisiblePosition(PreviousWordPosition(c.DeepEquivalent()));
 }
 
 Position StartOfWordPosition(const VisiblePosition& position, EWordSide side) {

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

@@ -451,7 +451,7 @@ TEST_P(ParameterizedVisibleUnitsWordTest, NextWordSkipTab) {
 
 //----
 
-TEST_F(VisibleUnitsWordTest, PreviousWordBasic) {
+TEST_P(ParameterizedVisibleUnitsWordTest, PreviousWordBasic) {
   EXPECT_EQ("<p> |(1) abc def</p>", DoPreviousWord("<p>| (1) abc def</p>"));
   EXPECT_EQ("<p> |(1) abc def</p>", DoPreviousWord("<p> |(1) abc def</p>"));
   EXPECT_EQ("<p> |(1) abc def</p>", DoPreviousWord("<p> (|1) abc def</p>"));