Basic Version Control with Merging

With a modern merging-based version control system (such as Git and Hg; see Merge-based vs Lock-based Version Control), C-x v v does the following when invoked from a buffer that visits a version-controlled file or a VC Directory or Dired buffer:

These rules also apply when you use RCS in its non-locking mode, except that changes are not automatically merged from the repository. Nothing informs you if another user has committed changes in the same file since you began editing it; when you commit your revision, that other user’s changes are removed (however, they remain in the repository and are thus not irrevocably lost). Therefore, you must verify that the current revision is unchanged before committing your changes. In addition, locking is possible with RCS even in this mode: C-x v v with an unmodified file locks the file, just as it does with RCS in its normal locking mode (see Basic Version Control with Locking).

If C-x v v is invoked from a buffer under Diff Mode, the command assumes the buffer holds a set of patches for one or more files. It then applies the changes to the respective files and commits the changes after popping up the *vc-log* buffer to allow you to type a suitable commit log message.