Fix setComposingText when newCursorPosition != 1

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

 /*
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2005 Alexey Proskuryakov.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 130 matching lines @@
                     resultEnd = textRunStartPosition;
                 else
                     resultEnd = textRunEndPosition;
             }
             docTextPosition += len;
             break;
         }
         docTextPosition += len;
     }
 
-    if (!startRangeFound)
-        return EphemeralRange();
+    if (!startRangeFound) {

[Changwan Ryu, 2016/04/04 06:23:13]

Could you leave some comment on how startRangeFound is related to the right
boundary exceeding case?
Also, is there any genuine case where we want to return empty ephemeral range?
e.g. there was no text information in this node.

[yabinh, 2016/04/04 08:31:51]

OK.
startRangeFound = start() >= docTextPosition && start() <= docTextPosition +
len.
The former ensure new cursor doesn't exceed the left boundary, and the latter
ensures the right boundary.

In the old implementation, it will return empty ephemeral range if and only if
new cursor exceeds the boundary.

+        // If cursor position exceeds the right boundary, it should stay at the right boundary
+        resultStart = textRunEndPosition;
+        resultEnd = textRunEndPosition;
+    }
 
     if (length() && end() > docTextPosition) { // end() is out of bounds
         resultEnd = textRunEndPosition;
     }
 
     return EphemeralRange(resultStart.toOffsetInAnchor(), resultEnd.toOffsetInAnchor());
 }
 
 PlainTextRange PlainTextRange::create(const ContainerNode& scope, const EphemeralRange& range)
 {
@@ skipping 17 matching lines @@
 
     return PlainTextRange(start, end);
 }
 
 PlainTextRange PlainTextRange::create(const ContainerNode& scope, const Range& range)
 {
     return create(scope, EphemeralRange(&range));
 }
 
 } // namespace blink