28.3.1 Change Log Commands

The Emacs command C-x 4 a adds a new entry to the change log file for the file you are editing (add-change-log-entry-other-window). If that file is actually a backup file, it makes an entry appropriate for the file’s parent—that is useful for making log entries for functions that have been deleted in the current version.

C-x 4 a visits the change log file and creates a new entry unless the most recent entry is for today’s date and your name. It also creates a new item for the current file. For many languages, it can even guess the name of the function or other object that was changed.

To find the change log file, Emacs searches up the directory tree from the file you are editing. By default, it stops if it finds a directory that seems to be the root of a version-control repository. To change this, customize change-log-directory-files.

When the variable add-log-keep-changes-together is non-nil, C-x 4 a adds to any existing item for the file, rather than starting a new item.

You can combine multiple changes of the same nature. If you don’t enter any text after the initial C-x 4 a, any subsequent C-x 4 a adds another symbol to the change log entry.

If add-log-always-start-new-record is non-nil, C-x 4 a always makes a new entry, even if the last entry was made by you and on the same date.

If the value of the variable change-log-version-info-enabled is non-nil, C-x 4 a adds the file’s version number to the change log entry. It finds the version number by searching the first ten percent of the file, using regular expressions from the variable change-log-version-number-regexp-list.

The change log file is visited in Change Log mode. In this major mode, each bunch of grouped items counts as one paragraph, and each entry is considered a page. This facilitates editing the entries. C-j and auto-fill indent each new line like the previous line; this is convenient for entering the contents of an entry.

You can use the command change-log-goto-source (by default bound to C-c C-c) to go to the source location of the change log entry near point, when Change Log mode is on. Then subsequent invocations of the next-error command (by default bound to M-g M-n and C-x `) will move between entries in the change log. You will jump to the actual site in the file that was changed, not just to the next change log entry. You can also use previous-error to move back through the change log entries.

You can use the command M-x change-log-merge to merge other log files into a buffer in Change Log Mode, preserving the date ordering of entries.

Version control systems are another way to keep track of changes in your program and keep a change log. Many projects that use a VCS don’t keep a separate versioned change log file nowadays, so you may wish to avoid having such a file in the repository. If the value of add-log-dont-create-changelog-file is non-nil, commands like C-x 4 a (add-change-log-entry-other-window) will record changes in a suitably named temporary buffer instead of a file, if such a file does not already exist.

Whether you have a change log file or use a temporary buffer for change logs, you can type C-c C-a (log-edit-insert-changelog) in the VC Log buffer to insert the relevant change log entries, if they exist. See Log Buffer.