Workaround for setComposition styling clobber

third_party/WebKit/Source/core/editing/InputMethodController.cpp

Index: third_party/WebKit/Source/core/editing/InputMethodController.cpp
diff --git a/third_party/WebKit/Source/core/editing/InputMethodController.cpp b/third_party/WebKit/Source/core/editing/InputMethodController.cpp
index f8628dc7e842b61d332d1ad4b0a6870b9b25a253..30b6a09b5a296d2a92fa9be4c9928f23f4d21c85 100644
--- a/third_party/WebKit/Source/core/editing/InputMethodController.cpp
+++ b/third_party/WebKit/Source/core/editing/InputMethodController.cpp
@@ -357,6 +357,154 @@ void InputMethodController::cancelCompositionIfSelectionIsInvalid() {
   frame().chromeClient().didCancelCompositionOnSelectionChange();
 }
 
+static size_t computeCommonPrefixLength(const String& str1,
+                                        const String& str2) {
+  const size_t maxCommonPrefixLength = std::min(str1.length(), str2.length());
+  for (size_t index = 0; index < maxCommonPrefixLength; ++index) {
+    if (str1[index] != str2[index])
+      return index;
+  }
+

[yosin_UTC9, 2016/10/12 06:35:37]

nit: Please remove an extra blank line.

[yabinh, 2016/10/12 07:32:32]

Done.

+  return maxCommonPrefixLength;
+}
+
+static size_t computeCommonSuffixLength(const String& str1,
+                                        const String& str2) {
+  const size_t length1 = str1.length();
+  const size_t length2 = str2.length();
+  const size_t maxCommonSuffixLength = std::min(length1, length2);
+  for (size_t index = 0; index < maxCommonSuffixLength; ++index) {
+    if (str1[length1 - index - 1] != str2[length2 - index - 1])
+      return index;
+  }
+

[yosin_UTC9, 2016/10/12 06:35:38]

nit: Please remove an extra blank line.

[yabinh, 2016/10/12 07:32:32]

Done.

+  return maxCommonSuffixLength;
+}
+
+static size_t computeCommonGraphemeClusterPrefixLengthForSetComposition(
+    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);
+  if (range.isNull())
+    return 0;
+  const Position& position = range.endPosition();
+  const Position& adjustedPosition = previousPositionOf(
+      nextPositionOf(position, PositionMoveType::GraphemeCluster),
+      PositionMoveType::GraphemeCluster);
+  DCHECK_EQ(position.anchorNode(), adjustedPosition.anchorNode());
+  const int diff = position.computeOffsetInContainerNode() -

[yosin_UTC9, 2016/10/12 06:35:37]

Let's do
DCHECK_GE(position.computeOffsetInContainerNode(),
          adjustedPosition.computeOffsetInContainerNode())
rather than
DCHECK_GE(diff, 0)
to print offset values for helping debug.

[yabinh, 2016/10/12 07:32:32]

Done.

+                   adjustedPosition.computeOffsetInContainerNode();
+  DCHECK_GE(diff, 0);
+  return commonPrefixLength - static_cast<size_t>(diff);
+}
+
+static size_t computeCommonGraphemeClusterSuffixLengthForSetComposition(
+    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)
+          .createRange(*rootEditableElement);
+  if (range.isNull())
+    return 0;
+  const Position& position = range.endPosition();
+  const Position& adjustedPosition = nextPositionOf(
+      previousPositionOf(position, PositionMoveType::GraphemeCluster),
+      PositionMoveType::GraphemeCluster);
+  DCHECK_EQ(position.anchorNode(), adjustedPosition.anchorNode());
+  const int diff = adjustedPosition.computeOffsetInContainerNode() -
+                   position.computeOffsetInContainerNode();
+  DCHECK_GE(diff, 0);

[yosin_UTC9, 2016/10/12 06:35:37]

Ditto as computeCommonGraphemeClusterPrefixLengthForSetComposition

[yabinh, 2016/10/12 07:32:33]

Done.

+  return commonSuffixLength - static_cast<size_t>(diff);
+}
+
+void InputMethodController::setCompositionWithIncrementalText(
+    const String& text,
+    const Vector<CompositionUnderline>& underlines,
+    int selectionStart,
+    int selectionEnd) {
+  Element* editable = frame().selection().rootEditableElement();
+  if (!editable)
+    return;
+
+  String composing = composingText();
+  const size_t commonPrefixLength =
+      computeCommonGraphemeClusterPrefixLengthForSetComposition(composing, text,
+                                                                editable);
+
+  // We should ignore common prefix when finding common suffix.
+  const size_t commonSuffixLength =
+      computeCommonGraphemeClusterSuffixLengthForSetComposition(
+          composing.right(composing.length() - commonPrefixLength),
+          text.right(text.length() - commonPrefixLength), editable);
+
+  const bool appending =

[yosin_UTC9, 2016/10/12 06:35:38]

s/appending/inserting/

[yabinh, 2016/10/12 07:32:32]

Done.

+      text.length() > commonPrefixLength + commonSuffixLength;
+  const bool subtracting =

[yosin_UTC9, 2016/10/12 06:35:37]

s/subtracting/deleting/

[yabinh, 2016/10/12 07:32:32]

Done.

+      composing.length() > commonPrefixLength + +commonSuffixLength;

[yosin_UTC9, 2016/10/12 06:35:38]

nit: Remove |+| before |comonSuffixLength|.

[yabinh, 2016/10/12 07:32:32]

Done.

+
+  if (appending || subtracting) {
+    // Select the text to be subtracted.

[yosin_UTC9, 2016/10/12 06:35:38]

s/subtracted/deleted/

[yabinh, 2016/10/12 07:32:32]

Done.

+    const size_t compositionStart =
+        PlainTextRange::create(*editable, compositionEphemeralRange()).start();
+    const size_t subtractionStart = compositionStart + commonPrefixLength;
+    const size_t subtractionEnd =
+        compositionStart + composing.length() - commonSuffixLength;
+    const EphemeralRange& subtractionRange =
+        PlainTextRange(subtractionStart, subtractionEnd).createRange(*editable);
+    VisibleSelection selection;
+    selection.setWithoutValidation(subtractionRange.startPosition(),
+                                   subtractionRange.endPosition());
+    const Document* currentDocument = frame().document();

[yosin_UTC9, 2016/10/12 06:35:37]

s/const Document*/Document* const/

[yabinh, 2016/10/12 07:32:32]

Done.

+    frame().selection().setSelection(selection, 0);
+    clear();
+
+    // FrameSeleciton::setSelection() can change document associate to |frame|.
+    if (*currentDocument != *frame().document())

[yosin_UTC9, 2016/10/12 06:35:38]

Remove |*|, we don't need to de-reference for comparison.

[yabinh, 2016/10/12 07:32:32]

Done.

+      return;
+    if (!currentDocument->focusedElement())
+      return;
+
+    // Append the incremental text.
+    const size_t appendingLength =
+        text.length() - commonPrefixLength - commonSuffixLength;
+    String appendingText = text.substring(commonPrefixLength, appendingLength);

[yosin_UTC9, 2016/10/12 06:35:37]

s/String/const String&/

[yabinh, 2016/10/12 07:32:33]

Done.

+    insertTextDuringCompositionWithEvents(frame(), appendingText,
+                                          TypingCommand::PreventSpellChecking,
+                                          TypingCommand::TextCompositionUpdate);
+
+    // Event handlers might destroy document.
+    if (!frame().document())

[yosin_UTC9, 2016/10/12 06:35:37]

No need to checking null document. |currentDocument != frame().document()| is
suffice.

[yabinh, 2016/10/12 07:32:32]

Done.

+      return;
+    if (*currentDocument != *frame().document())
+      return;
+
+    // TODO(yosin): The use of updateStyleAndLayoutIgnorePendingStylesheets
+    // needs to be audited. see http://crbug.com/590369 for more details.
+    frame().document()->updateStyleAndLayoutIgnorePendingStylesheets();
+
+    // Now recreate the composition starting at its original start, and
+    // apply the specified final selection offsets.
+    setCompositionFromExistingText(underlines, compositionStart,
+                                   compositionStart + text.length());
+  }
+
+  selectComposition();
+  const PlainTextRange& selectedRange = createSelectionRangeForSetComposition(
+      selectionStart, selectionEnd, text.length());
+  // We shouldn't close typing in the middle of setComposition.
+  setEditableSelectionOffsets(selectedRange, NotUserTriggered);
+  m_isDirty = true;
+}
+
 void InputMethodController::setComposition(
     const String& text,
     const Vector<CompositionUnderline>& underlines,
@@ -369,6 +517,14 @@ void InputMethodController::setComposition(
   // See https://bugs.webkit.org/show_bug.cgi?id=46868
   frame().document()->updateStyleAndLayoutTree();
 
+  // When the IME only wants to change a few characters at the end of the
+  // composition, only touch those characters in order to preserve rich text
+  // substructure.
+  if (hasComposition() && text.length()) {
+    return setCompositionWithIncrementalText(text, underlines, selectionStart,
+                                             selectionEnd);
+  }
+
   selectComposition();
 
   if (frame().selection().isNone())
@@ -378,15 +534,8 @@ void InputMethodController::setComposition(
   if (!target)
     return;
 
-  // TODO(xiaochengh): The use of updateStyleAndLayoutIgnorePendingStylesheets
-  // needs to be audited. see http://crbug.com/590369 for more details.
-  frame().document()->updateStyleAndLayoutIgnorePendingStylesheets();
-
-  int selectionOffsetsStart = static_cast<int>(getSelectionOffsets().start());
-  int start = selectionOffsetsStart + selectionStart;
-  int end = selectionOffsetsStart + selectionEnd;
-  PlainTextRange selectedRange =
-      createRangeForSelection(start, end, text.length());
+  PlainTextRange selectedRange = createSelectionRangeForSetComposition(
+      selectionStart, selectionEnd, text.length());
 
   // Dispatch an appropriate composition event to the focused node.
   // We check the composition status and choose an appropriate composition event
@@ -503,6 +652,21 @@ void InputMethodController::setComposition(
   }
 }
 
+PlainTextRange InputMethodController::createSelectionRangeForSetComposition(
+    int selectionStart,
+    int selectionEnd,
+    size_t textLength) const {
+  // TODO(xiaochengh): The use of updateStyleAndLayoutIgnorePendingStylesheets
+  // needs to be audited. see http://crbug.com/590369 for more details.
+  frame().document()->updateStyleAndLayoutIgnorePendingStylesheets();

[yosin_UTC9, 2016/10/12 06:35:37]

This code fragment should be in callers rather than newly introduced function.

[yabinh, 2016/10/12 07:32:33]

Done.

+
+  const int selectionOffsetsStart =
+      static_cast<int>(getSelectionOffsets().start());
+  int start = selectionOffsetsStart + selectionStart;

[yosin_UTC9, 2016/10/12 06:35:37]

s/int/const int/

[yabinh, 2016/10/12 07:32:32]

Done.

+  int end = selectionOffsetsStart + selectionEnd;

[yosin_UTC9, 2016/10/12 06:35:37]

s/int/const int/

[yabinh, 2016/10/12 07:32:32]

Done.

+  return createRangeForSelection(start, end, textLength);
+}
+
 void InputMethodController::setCompositionFromExistingText(
     const Vector<CompositionUnderline>& underlines,
     unsigned compositionStart,