Emacs supports programmable completion in a couple of modes through a
feature called pcomplete. This
article
goes into more detail. For reference, this is what I have in my Emacs
config file (code mostly from that article):
(defun pcmpl-git-commands ()
"Return the most common git commands by parsing the git output."
(with-temp-buffer
(call-process-shell-command "git" nil (current-buffer) nil "help" "--all")
(goto-char 0)
(search-forward "Main Porcelain Commands")
(let (commands)
(while (re-search-forward
"^[[:blank:]]+\\([[:word:]-.]+\\)[[:blank:]]*\\([[:word:]-.]+\\)?"
nil t)
(push (match-string 1) commands)
(when (match-string 2)
(push (match-string 2) commands)))
(sort commands #'string<))))
(defconst pcmpl-git-commands (pcmpl-git-commands)
"List of `git' commands.")
(defvar pcmpl-git-ref-list-cmd "git for-each-ref refs/ --format='%(refname)'"
"The `git' command to run to get a list of refs.")
(defun pcmpl-git-get-refs (type)
"Return a list of `git' refs filtered by TYPE."
(with-temp-buffer
(insert (shell-command-to-string pcmpl-git-ref-list-cmd))
(goto-char (point-min))
(let (refs)
(while (re-search-forward (concat "^refs/" type "/\\(.+\\)$") nil t)
(push (match-string 1) refs))
(nreverse refs))))
(defun pcmpl-git-remotes ()
"Return a list of remote repositories."
(split-string (shell-command-to-string "git remote")))
(defun pcomplete/git ()
"Completion for `git'."
;; Completion for the command argument.
(pcomplete-here* pcmpl-git-commands)
(cond
((pcomplete-match "help" 1)
(pcomplete-here* pcmpl-git-commands))
((pcomplete-match (regexp-opt '("pull" "push")) 1)
(pcomplete-here (pcmpl-git-remotes)))
;; provide branch completion for the command `checkout'.
((pcomplete-match "checkout" 1)
(pcomplete-here* (append (pcmpl-git-get-refs "heads")
(pcmpl-git-get-refs "tags"))))
(t
(while (pcomplete-here (pcomplete-entries))))))
Unfortunately, git help doesn’t give a machine-parsable list of
commands, so the first function which tries to identify them is sort
of a hack. But, as you can see, it’s fairly straightforward to add
your own complete functions. I think I’ll use it as an excuse to learn
more Emacs Lisp.