Fix setComposingText when newCursorPosition != 1

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 7aeb0d1f45878ec10d499195a6e38f8e40180923..89d9017dd73a84876001fe0f70e4733a8e58534d 100644
--- a/third_party/WebKit/Source/core/editing/InputMethodController.cpp
+++ b/third_party/WebKit/Source/core/editing/InputMethodController.cpp
@@ -231,7 +231,7 @@ void InputMethodController::cancelCompositionIfSelectionIsInvalid()
     frame().chromeClient().didCancelCompositionOnSelectionChange();
 }
 
-void InputMethodController::setComposition(const String& text, const Vector<CompositionUnderline>& underlines, unsigned selectionStart, unsigned selectionEnd)
+void InputMethodController::setComposition(const String& text, const Vector<CompositionUnderline>& underlines, int selectionStart, int selectionEnd)
 {
     Editor::RevealSelectionScope revealSelectionScope(&editor());
 
@@ -319,8 +319,8 @@ void InputMethodController::setComposition(const String& text, const Vector<Comp
     if (baseNode->layoutObject())
         baseNode->layoutObject()->setShouldDoFullPaintInvalidation();
 
-    unsigned start = std::min(baseOffset + selectionStart, extentOffset);
-    unsigned end = std::min(std::max(start, baseOffset + selectionEnd), extentOffset);
+    int start = std::min(std::max((int)baseOffset + selectionStart, 0), (int)extentOffset);

[Changwan Ryu, 2016/04/01 00:37:26]

baseOffset >= 0 so you just need to make sure selectionStart >= 0. I believe
that should happen in some other place.

[yabinh, 2016/04/01 04:14:17]

selectionStart can be negative, because it is the relative position of the
cursor.
If newCursorPosition < 1, selectionStart = newCursorPosition; If
newCursorPosition >= 1, selectionStart = newCursorPosition + text.length() - 1.

[Changwan Ryu, 2016/04/01 05:36:15]

I see. Thanks for clarification.
By the way, we prefer using static casting to c-style casting. So it should be
static_cast<int>(baseOffset). Also you'll need unit tests around the changed
behavior in Blink.

I was a bit worried that there would be a slight chance of overflow converting
from unsigned to int, but there are so many other places 
which does it incorrectly. I'll punt unsigned-int conversion issues to aelias@.

+    int end = std::min(std::max((int)baseOffset + selectionEnd, start), (int)extentOffset);
     RefPtrWillBeRawPtr<Range> selectedRange = Range::create(baseNode->document(), baseNode, start, baseNode, end);
     frame().selection().setSelectedRange(selectedRange.get(), TextAffinity::Downstream, SelectionDirectionalMode::NonDirectional, NotUserTriggered);