Register the visited file for version control.
The command C-x v i (vc-register) registers each
file in the current VC fileset, placing it under version control.
This is essentially equivalent to the action of C-x v v on an
unregistered VC fileset (see Basic Editing under Version Control), except that if the
VC fileset is already registered, C-x v i signals an error
whereas C-x v v performs some other action.
To register a file, Emacs must choose a version control system. For
a multi-file VC fileset, the VC Directory buffer specifies the system
to use (see VC Directory Mode). For a single-file VC fileset, if
the file’s directory already contains files registered in a version
control system, or if the directory is part of a directory tree
controlled by a version control system, Emacs chooses that system. In
the event that more than one version control system is applicable,
Emacs uses the one that appears first in the variable
vc-handled-backends (see Customizing VC).
If Emacs cannot find a version control system to register the file
under, it prompts for a repository type, creates a new repository, and
registers the file into that repository.
On most version control systems, registering a file with C-x v i or C-x v v adds it to the working tree but not to the repository. Such files are labeled as ‘added’ in the VC Directory buffer, and show a revision ID of ‘@@’ in the mode line. To make the registration take effect in the repository, you must perform a commit (see Basic Editing under Version Control). Note that a single commit can include both file additions and edits to existing files.
On a locking-based version control system (see Merge-based vs Lock-based Version Control), registering a file leaves it unlocked and read-only. Type C-x v v to start editing it.