Fix a bug when inputting text after grapheme cluster

third_party/WebKit/Source/core/editing/commands/InsertIncrementalTextCommand.cpp

 // Copyright (c) 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/editing/commands/InsertIncrementalTextCommand.h"
 
 #include "core/dom/Document.h"
 #include "core/dom/Element.h"
 #include "core/dom/Text.h"
 #include "core/editing/EditingUtilities.h"
@@ skipping 34 matching lines @@
       nextPositionOf(position, PositionMoveType::GraphemeCluster),
       PositionMoveType::GraphemeCluster);
   DCHECK_EQ(position.anchorNode(), adjustedPosition.anchorNode());
   DCHECK_GE(position.computeOffsetInContainerNode(),
             adjustedPosition.computeOffsetInContainerNode());
   return static_cast<size_t>(position.computeOffsetInContainerNode() -
                              adjustedPosition.computeOffsetInContainerNode());
 }
 
 size_t computeCommonGraphemeClusterPrefixLength(
+    const int selectionStart,
     const String& oldText,
     const String& newText,
     const Element* rootEditableElement) {
   const size_t commonPrefixLength = computeCommonPrefixLength(oldText, newText);
 
   // For grapheme cluster, we should adjust it for grapheme boundary.
   const EphemeralRange& range =
-      PlainTextRange(0, commonPrefixLength).createRange(*rootEditableElement);
+      PlainTextRange(0, selectionStart + commonPrefixLength)
+          .createRange(*rootEditableElement);
   if (range.isNull())
     return 0;
   const Position& position = range.endPosition();
   const size_t diff = computeDistanceToLeftGraphemeBoundary(position);
   DCHECK_GE(commonPrefixLength, diff);
   return commonPrefixLength - diff;
 }
 
 // If current position is at grapheme boundary, return 0; otherwise, return the
 // distance to its nearest right grapheme boundary.
 size_t computeDistanceToRightGraphemeBoundary(const Position& position) {
   const Position& adjustedPosition = nextPositionOf(
       previousPositionOf(position, PositionMoveType::GraphemeCluster),
       PositionMoveType::GraphemeCluster);
   DCHECK_EQ(position.anchorNode(), adjustedPosition.anchorNode());
   DCHECK_GE(adjustedPosition.computeOffsetInContainerNode(),
             position.computeOffsetInContainerNode());
   return static_cast<size_t>(adjustedPosition.computeOffsetInContainerNode() -
                              position.computeOffsetInContainerNode());
 }
 
 size_t computeCommonGraphemeClusterSuffixLength(
+    const int selectionStart,
     const String& oldText,
     const String& newText,
     const Element* rootEditableElement) {
   const size_t commonSuffixLength = computeCommonSuffixLength(oldText, newText);
 
   // For grapheme cluster, we should adjust it for grapheme boundary.
   const EphemeralRange& range =
-      PlainTextRange(0, oldText.length() - commonSuffixLength)
+      PlainTextRange(0, selectionStart + oldText.length() - commonSuffixLength)
           .createRange(*rootEditableElement);
   if (range.isNull())
     return 0;
   const Position& position = range.endPosition();
   const size_t diff = computeDistanceToRightGraphemeBoundary(position);
   DCHECK_GE(commonSuffixLength, diff);
   return commonSuffixLength - diff;
 }
 
 const String computeTextForInsertion(const String& newText,
@@ skipping 40 matching lines @@
 
 void InsertIncrementalTextCommand::doApply(EditingState* editingState) {
   const Element* element = endingSelection().rootEditableElement();
   DCHECK(element);
 
   const EphemeralRange selectionRange(endingSelection().start(),
                                       endingSelection().end());
   const String oldText = plainText(selectionRange);
   const String& newText = m_text;
 
+  const int selectionStart =
+      endingSelection().start().computeOffsetInContainerNode();
   const size_t newTextLength = newText.length();
   const size_t oldTextLength = oldText.length();
-  const size_t commonPrefixLength =
-      computeCommonGraphemeClusterPrefixLength(oldText, newText, element);
+  const size_t commonPrefixLength = computeCommonGraphemeClusterPrefixLength(
+      selectionStart, oldText, newText, element);
   // We should ignore common prefix when finding common suffix.
   const size_t commonSuffixLength = computeCommonGraphemeClusterSuffixLength(
-      oldText.right(oldTextLength - commonPrefixLength),
+      selectionStart, oldText.right(oldTextLength - commonPrefixLength),
       newText.right(newTextLength - commonPrefixLength), element);
   DCHECK_GE(oldTextLength, commonPrefixLength + commonSuffixLength);
 
   m_text =
       computeTextForInsertion(m_text, commonPrefixLength, commonSuffixLength);
 
   const int offset = static_cast<int>(commonPrefixLength);
   const int length =
       static_cast<int>(oldTextLength - commonPrefixLength - commonSuffixLength);
   const VisibleSelection& selectionForInsertion = computeSelectionForInsertion(
       selectionRange, offset, length, endingSelection().isDirectional());
 
   setEndingSelectionWithoutValidation(selectionForInsertion.start(),
                                       selectionForInsertion.end());
 
   InsertTextCommand::doApply(editingState);
 }
 
 }  // namespace blink