The commit messages in source code repositories are valuable but not easy to be
generated manually in time for tracking issues, reporting bugs, and understanding codes.
Recently published works indicated that the deep neural machine translation approaches
have drawn considerable attentions on automatic generation of commit messages.
However, they could not deal with out-of-vocabulary (OOV) words, which are essential
context-specific identifiers such as class names and method names in code diffs. In this …