-@node Remote Repositories
-@subsection Remote Repositories
-@cindex remote repositories
-
- A common way of using CVS and other more advanced VCSes is to set up
-a central repository on some Internet host, then have each
-developer check out a personal working copy of the files on his local
-machine. Committing changes to the repository, and picking up changes
-from other users into one's own working area, then works by direct
-interactions with the repository server.
-
- One difficulty is that access to a repository server is often slow,
-and that developers might need to work off-line as well. While only
-third-generation decentralized VCses such as GNU Arch or Mercurial
-really solve this problem, VC is designed to reduce the amount of
-network interaction necessary.
-
- If you are using a truly decentralized VCS you can skip the rest of
-this section. It describes backup and local-repository techniques
-that are only useful for Subversion and earlier VCSes.
-
-@menu
-* Version Backups:: Keeping local copies of repository versions.
-* Local Version Control:: Using another version system for local editing.
-@end menu
-
-@node Version Backups
-@subsubsection Version Backups
-@cindex version backups
-
-@cindex automatic version backups
- When VC sees that the repository for a file is on a remote
-machine, it automatically makes local backups of unmodified versions
-of the file---@dfn{automatic version backups}. This means that you
-can compare the file to the repository version (@kbd{C-x v =}), or
-revert to that version (@kbd{C-x v u}), without any network
-interactions.
-
- The local copy of the unmodified file is called a @dfn{version
-backup} to indicate that it corresponds exactly to a version that is
-stored in the repository. Note that version backups are not the same
-as ordinary Emacs backup files
-@iftex
-(@pxref{Backup,,,emacs, the Emacs Manual}).
-@end iftex
-@ifnottex
-(@pxref{Backup}).
-@end ifnottex
-But they follow a similar naming convention.
-
- For a file that comes from a remote repository, VC makes a
-version backup whenever you save the first changes to the file, and
-removes it after you have committed your modified version to the
-repository. You can disable the making of automatic version backups by
-setting @code{vc-cvs-stay-local} to @code{nil} (@pxref{CVS Options}).
-
-@cindex manual version backups
- The name of the automatic version backup for version @var{version}
-of file @var{file} is @code{@var{file}.~@var{version}.~}. This is
-almost the same as the name used by @kbd{C-x v ~}
-@iftex
-(@pxref{Old Revisions,,,emacs, the Emacs Manual}),
-@end iftex
-@ifnottex
-(@pxref{Old Revisions}),
-@end ifnottex
-the only difference being the additional dot (@samp{.}) after the
-version number. This similarity is intentional, because both kinds of
-files store the same kind of information. The file made by @kbd{C-x v
-~} acts as a @dfn{manual version backup}.
-
- All the VC commands that operate on old versions of a file can use
-both kinds of version backups. For instance, @kbd{C-x v ~} uses
-either an automatic or a manual version backup, if possible, to get
-the contents of the version you request. Likewise, @kbd{C-x v =} and
-@kbd{C-x v u} use either an automatic or a manual version backup, if
-one of them exists, to get the contents of a version to compare or
-revert to. If you changed a file outside of Emacs, so that no
-automatic version backup was created for the previous text, you can
-create a manual backup of that version using @kbd{C-x v ~}, and thus
-obtain the benefit of the local copy for Emacs commands.
-
- The only difference in Emacs's handling of manual and automatic
-version backups, once they exist, is that Emacs deletes automatic
-version backups when you commit to the repository. By contrast,
-manual version backups remain until you delete them.
-
-@node Local Version Control
-@subsubsection Local Version Control
-@cindex local version control
-@cindex local back end (version control)
-
-When you make many changes to a file that comes from a remote
-repository, it can be convenient to have version control on your local
-machine as well. You can then record intermediate versions, revert to
-a previous state, etc., before you actually commit your changes to the
-remote server.
-
-VC lets you do this by putting a file under a second, local version
-control system, so that the file is effectively registered in two
-systems at the same time. For the description here, we will assume
-that the remote system is CVS, and you use RCS locally, although the
-mechanism works with any combination of version control systems
-(@dfn{back ends}).
-
-To make it work with other back ends, you must make sure that the
-``more local'' back end comes before the ``more remote'' back end in
-the setting of @code{vc-handled-backends} (@pxref{Customizing VC}). By
-default, this variable is set up so that you can use remote CVS and
-local RCS as described here.
-
-To start using local RCS for a file that comes from a remote CVS
-server, you must @emph{register the file in RCS}, by typing @kbd{C-u
-C-x v v rcs @key{RET}}. (In other words, use @code{vc-next-action} with a
-prefix argument, and specify RCS as the back end.)
-
-You can do this at any time; it does not matter whether you have
-already modified the file with respect to the version in the CVS
-repository. If possible, VC tries to make the RCS master start with
-the unmodified repository version, then checks in any local changes
-as a new version. This works if you have not made any changes yet, or
-if the unmodified repository version exists locally as a version
-backup (@pxref{Version Backups}). If the unmodified version is not
-available locally, the RCS master starts with the modified version;
-the only drawback to this is that you cannot compare your changes
-locally to what is stored in the repository.
-
-The version number of the RCS master is derived from the current CVS
-version, starting a branch from it. For example, if the current CVS
-version is 1.23, the local RCS branch will be 1.23.1. Version 1.23 in
-the RCS master will be identical to version 1.23 under CVS; your first
-changes are checked in as 1.23.1.1. (If the unmodified file is not
-available locally, VC will check in the modified file twice, both as
-1.23 and 1.23.1.1, to make the revision numbers consistent.)
-
-If you do not use locking under CVS (the default), locking is also
-disabled for RCS, so that editing under RCS works exactly as under
-CVS.
-
-When you are done with local editing, you can commit the final version
-back to the CVS repository by typing @kbd{C-u C-x v v cvs @key{RET}}.
-This initializes the log entry buffer
-@iftex
-(@pxref{Log Buffer,,,emacs, the Emacs Manual})
-@end iftex
-@ifnottex
-(@pxref{Log Buffer})
-@end ifnottex
-to contain all the log entries you have recorded in the RCS master;
-you can edit them as you wish, and then commit in CVS by typing
-@kbd{C-c C-c}. If the commit is successful, VC removes the RCS
-master, so that the file is once again registered under CVS only.
-(The RCS master is not actually deleted, just renamed by appending
-@samp{~} to the name, so that you can refer to it later if you wish.)
-
-While using local RCS, you can pick up recent changes from the CVS
-repository into your local file, or commit some of your changes back
-to CVS, without terminating local RCS version control. To do this,
-switch to the CVS back end temporarily, with the @kbd{C-x v b} command:
-
-@table @kbd
-@item C-x v b
-Switch to another back end that the current file is registered
-under (@code{vc-switch-backend}).
-
-@item C-u C-x v b @var{backend} @key{RET}
-Switch to @var{backend} for the current file.
-@end table
-
-@kindex C-x v b
-@findex vc-switch-backend
-@kbd{C-x v b} does not change the buffer contents, or any files; it
-only changes VC's perspective on how to handle the file. Any
-subsequent VC commands for that file will operate on the back end that
-is currently selected.
-
-If the current file is registered in more than one back end, typing
-@kbd{C-x v b} ``cycles'' through all of these back ends. With a
-prefix argument, it asks for the back end to use in the minibuffer.
-
-Thus, if you are using local RCS, and you want to pick up some recent
-changes in the file from remote CVS, first visit the file, then type
-@kbd{C-x v b} to switch to CVS, and finally use @kbd{C-x v m
-@key{RET}} to merge the news
-@iftex
-(@pxref{Merging,,,emacs, the Emacs Manual}).
-@end iftex
-@ifnottex
-(@pxref{Merging}).
-@end ifnottex
-You can then switch back to RCS by typing @kbd{C-x v b} again, and
-continue to edit locally.
-
-But if you do this, the revision numbers in the RCS master no longer
-correspond to those of CVS. Technically, this is not a problem, but
-it can become difficult to keep track of what is in the CVS repository
-and what is not. So we suggest that you return from time to time to
-CVS-only operation, by committing your local changes back to the
-repository using @kbd{C-u C-x v v cvs @key{RET}}.
-
-@node Revision Tags
-@subsection Revision Tags
-@cindex tags and version control
-
- In a VCS with per-file revision numbers (such as SCCS, RCS, or CVS)
-@dfn{tag} is a named set of file versions (one for each registered
-file) that you can treat as a unit. In a VCS with per-repository
-version numbers (Subversion and most later ones) a tag is simply
-a symbolic name for a revision.
-
- One important kind of tag is a @dfn{release}, a (theoretically)
-stable version of the system that is ready for distribution to users.
-
-@menu
-* Making Revision Tags:: The tag facilities.
-* Revision Tag Caveats:: Things to be careful of when using tags.
-@end menu
-
-@node Making Revision Tags
-@subsubsection Making and Using Revision Tags
-
- There are two basic commands for tags; one makes a
-tag with a given name, the other retrieves a named tag.
-
-@table @code
-@kindex C-x v s
-@findex vc-create-tag
-@item C-x v s @var{name} @key{RET}
-Define the working revision of every registered file in or under the
-current directory as a tag named @var{name}
-(@code{vc-create-tag}).
-
-@kindex C-x v r
-@findex vc-retrieve-tag
-@item C-x v r @var{name} @key{RET}
-For all registered files at or below the current directory level,
-retrieve the tagged revision @var{name}. This command will
-switch to a branch if @var{name} is a branch name and your VCS
-distinguishes branches from tags.
-(@code{vc-retrieve-tag}).
-
-This command reports an error if any files are locked at or below the
-current directory, without changing anything; this is to avoid
-overwriting work in progress.
-@end table
-
-Tags are inexpensive, so you need not hesitate to create them whenever
-they are useful. Branches vary in cost depending on your VCS; in
-older ones they may be expensive.
-
- You can give a tag or branch name as an argument to @kbd{C-x v =} or
-@kbd{C-x v ~}
-@iftex
-(@pxref{Old Revisions,,,emacs, the Emacs Manual}).
-@end iftex
-@ifnottex
-(@pxref{Old Revisions}).
-@end ifnottex
-Thus, you can use it to compare a tagged version against the current files,
-or two tagged versions against each other.
-
-@node Revision Tag Caveats
-@subsubsection Revision Tag Caveats
-
- For SCCS, VC implements tags itself; these tags are visible only
-through VC. Most later systems (including CVS, Subversion, bzr, git,
-and hg) have a native tag facility, and VC uses it where
-available; those tags will be visible even when you bypass VC.
-
- There is no support for VC tags using GNU Arch yet.
-
- Under older VCSes (SCCS, RCS, CVS, early versions of Subversion),
-renaming and deletion could create some difficulties with tags. This is
-not a VC-specific problem, but a general design issue in version
-control systems that was not solved effectively until the earliest
-third-generation systems.
-
- In a file-oriented VCS, when you rename a registered file you need
-to rename its master along with it; the command @code{vc-rename-file}
-will do this automatically. If you are using SCCS, you must also
-update the records of the tag, to mention the file by its new name
-(@code{vc-rename-file} does this, too). An old tag that refers to a
-master file that no longer exists under the recorded name is invalid;
-VC can no longer retrieve it. It would be beyond the scope of this
-manual to explain enough about RCS and SCCS to explain how to update
-the tags by hand.
-
- Using @code{vc-rename-file} makes the tag remain valid for
-retrieval, but it does not solve all problems. For example, some of the
-files in your program probably refer to others by name. At the very
-least, the makefile probably mentions the file that you renamed. If you
-retrieve an old tag, the renamed file is retrieved under its new
-name, which is not the name that the makefile expects. So the program
-won't really work as retrieved.
-