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 df935114b462563caaec2e0304e1baef383c096a..84dc6673e0bccb51c3c1d1a1b046781ed25a363f 100644
--- a/third_party/WebKit/Source/core/editing/InputMethodController.cpp
+++ b/third_party/WebKit/Source/core/editing/InputMethodController.cpp
@@ -338,6 +338,16 @@ void InputMethodController::cancelCompositionIfSelectionIsInvalid()
     frame().chromeClient().didCancelCompositionOnSelectionChange();
 }
 
+static size_t computeCommonPrefixLength(const String& str1, const String& str2)
+{
+    size_t commonPrefixLength = 0;
+    size_t length1 = str1.length();
+    size_t length2 = str2.length();
+    while (commonPrefixLength < length1 && commonPrefixLength < length2 && str1[commonPrefixLength] == str2[commonPrefixLength])

[Changwan Ryu, 2016/09/27 05:23:03]

Can you skip a loop for surrogate pairs? Things can get weird if we apply
different formats to surrogate head and tail.

[yabinh, 2016/09/27 08:47:20]

Done.

+        commonPrefixLength++;
+    return commonPrefixLength;
+}
+
 void InputMethodController::setComposition(const String& text, const Vector<CompositionUnderline>& underlines, int selectionStart, int selectionEnd)
 {
     Editor::RevealSelectionScope revealSelectionScope(&editor());
@@ -347,6 +357,58 @@ void InputMethodController::setComposition(const String& text, const Vector<Comp
     // 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()) {
+        String composing = composingText();
+        size_t commonPrefixLength = computeCommonPrefixLength(composing, text);
+
+        bool appending = text.length() > commonPrefixLength;
+        bool backspacing = composing.length() > commonPrefixLength;
+        if (appending || backspacing) {
+            const EphemeralRange range = compositionEphemeralRange();
+            Element* editable = frame().selection().rootEditableElement();
+            if (!editable)
+                return;
+
+            // Move selection to the end of the composition.
+            PlainTextRange compositionPlainOffsets = PlainTextRange::create(*editable, range);
+            VisibleSelection selection;
+            selection.setWithoutValidation(range.endPosition(), range.endPosition());
+            frame().selection().setSelection(selection, 0);
+            clear();
+
+            Element* target = frame().document()->focusedElement();
+            if (!target)
+                return;
+
+            // Apply the incremental change.
+            if (backspacing)
+                extendSelectionAndDelete(composing.length() - commonPrefixLength, 0);

[aelias_OOO_until_Jul13, 2016/09/27 04:55:58]

Hmm, this has the same JS event problem as the other case you just fixed.  How
about selecting all the non-shared suffix characters in the selection logic
above, and then just always calling insertTextDuringCompositionWithEvents()
(possibly with "" for the backspacing case) and relying on the replacement of
selection?

[yabinh, 2016/09/27 08:47:20]

Done.

+            if (appending)
+                insertTextDuringCompositionWithEvents(frame(), text.substring(commonPrefixLength), TypingCommand::PreventSpellChecking, TypingCommand::TextCompositionUpdate);
+
+            // Event handlers might destroy document.
+            if (!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, compositionPlainOffsets.start(), compositionPlainOffsets.start() + text.length());
+            selectComposition();
+            PlainTextRange selectedRange = createSelectionRangeForSetComposition(selectionStart, selectionEnd, text.length());
+            // We shouldn't close typing in the middle of setComposition.
+            setEditableSelectionOffsets(selectedRange, NotUserTriggered);
+            m_isDirty = true;
+            return;
+        }
+    }
+
     selectComposition();
 
     if (frame().selection().isNone())
@@ -356,14 +418,7 @@ void InputMethodController::setComposition(const String& text, const Vector<Comp
     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 since this
@@ -466,6 +521,18 @@ void InputMethodController::setComposition(const String& text, const Vector<Comp
     }
 }
 
+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();
+
+    int selectionOffsetsStart = static_cast<int>(getSelectionOffsets().start());
+    int start = selectionOffsetsStart + selectionStart;
+    int end = selectionOffsetsStart + selectionEnd;
+    return createRangeForSelection(start, end, textLength);
+}
+
 void InputMethodController::setCompositionFromExistingText(const Vector<CompositionUnderline>& underlines, unsigned compositionStart, unsigned compositionEnd)
 {
     Element* editable = frame().selection().rootEditableElement();