use nonstandard `.git` directory with magit

Question

I have been using the setup described on the top comment here to manage my dotfiles using git. In short, I have this in my .bashrc:

alias config='/usr/bin/env git --git-dir=$HOME/.myconf/ --work-tree=$HOME'

I then can run any git command using config add <file>, etc. Is there anyway to get this working with magit, so I can commit changes to my configuration files without dropping into a shell?

Answer 1

In reviewing the magit project and its code, clearly the magit project opinion is to not set global configuration of the git directory, and with clear reasons. (#2939, #3516)

That said, this is your Emacs, and RMS et al want you to hack it. If you are running an Emacs session exclusively for the purpose of editing a repository with a nonstandard git directory, then magit's magit-git-global-arguments configuration provides a suitable hook.

;;; Configure magit to use .myconf (and not .git) as the git
;;; directory when a .myconf directory is found in the current
;;; working directory (which Emacs calls its `default-directory'
;;; per buffer) and there is no .git directory.
;;;
;;; For example, if dotfiles are tracked with a git directory at
;;; $HOME/.myconf, and the Emacs process starts from $HOME (and
;;; nothing in its configuration changes its `default-directory'
;;; in the current buffer), this will configure magit to use
;;; .myconf as the git directory.
;;;
;;; NOTE: This setting will apply for the entire Emacs process,
;;; regardless of magit invocation in other directories.
(unless (boundp 'myconf-magit-hook?)
  ;; Only run this hook once, even if Emacs reloads configuration.
  (eval-after-load 'magit
    '(let ((myconf-path (expand-file-name ".myconf")))
       (when (and (file-exists-p myconf-path)
                  (not (file-exists-p ".git")))
         ;; Insert git directory and working tree into magit's git
         ;; global arguments, while preserving magit's existing
         ;; command-line settings; `add-to-list' adds to the
         ;; beginning of the list.
         (add-to-list 'magit-git-global-arguments
                      (format "--work-tree=%s"
                              ;; Drop trailing slash.
                              (directory-file-name
                               ;; Get directory part (`dirname`).
                               (file-name-directory myconf-path))))
         (add-to-list 'magit-git-global-arguments
                      (format "--git-dir=%s" myconf-path)))))
  (setq myconf-magit-hook? t))

I tested this on GNU Emacs 26.1 with Magit 2.90.1, and I made it a point to avoid any Emacs Lisp features added in the past few years.

It would be convenient to configure magit to look for a nonstandard .git directory in the current buffer's default-directory, but short of monkeypatching (or a fork / pull request), I don't know of a way to configure that (given how global variables are used). Note that magit's design is intended to support multiple repositories within the same Emacs process, and has first-class interactions for a list of repositories.

I have been tracking $HOME files with git and a nonstandard git directory for 9 years. The use case: It's extremely common to run git in a subdirectory of $HOME and a nonstandard git directory for dotfiles will ensure that git never accidentally runs against the $HOME repository when there's no intermediate .git directory when git walks up the directory tree. It's clear from the OP's alias command that this is exactly the use case.

Personally, I run an Emacs session per project.

Answer 2

I use slightly-modifed @rduplain's approach with tweaking magit-git-global-arguments. This allows for working with standard and non-standard directories at different times within the same Emacs session (not concurrently), at the small price of having a separate shortcut for launching Magit with non-standard directory configured.

;; prepare the arguments
(setq dotfiles-git-dir (concat "--git-dir=" (expand-file-name "~/.dotfiles")))
(setq dotfiles-work-tree (concat "--work-tree=" (expand-file-name "~")))

;; function to start magit on dotfiles
(defun dotfiles-magit-status ()
  (interactive)
  (add-to-list 'magit-git-global-arguments dotfiles-git-dir)
  (add-to-list 'magit-git-global-arguments dotfiles-work-tree)
  (call-interactively 'magit-status))
(global-set-key (kbd "F5 d") 'dotfiles-magit-status)

;; wrapper to remove additional args before starting magit
(defun magit-status-with-removed-dotfiles-args ()
  (interactive)
  (setq magit-git-global-arguments (remove dotfiles-git-dir magit-git-global-arguments))
  (setq magit-git-global-arguments (remove dotfiles-work-tree magit-git-global-arguments))
  (call-interactively 'magit-status))
;; redirect global magit hotkey to our wrapper
(global-set-key (kbd "C-x g") 'magit-status-with-removed-dotfiles-args)
(define-key magit-file-mode-map (kbd "C-x g") 'magit-status-with-removed-dotfiles-args)

Answer 3

This won't work. I recommend you set it up like this instead:

cd $HOME
cat "gitdir: ./.myconf" > .git
cd .myconf                     # conceptually, not really necessary
git config core.worktree ./

At that point git and thus magit know that $HOME is a working tree and where the data is.

Then again, it seems that's what you are trying to prevent (at least for git, why not for magit also?). Because otherwise what is the benefit of storing the git data in $HOME/.myconf instead of in $HOME/.git?

If that is so, then I have another question: what's the benefit of that? I mean I see the appeal of vcsh (which also won't work with Magit), it allows you to use different repositories for the configuration files of multiple packages even though they are all in the same place. But from what you have said, it doesn't appear that this is what you are after.

So it seems the answer is "you can't". In theory you could advice a bunch of Magit functions, and that might kind of work - but there would be bugs, and you would be solely responsible for dealing with them. I would strongly recommend against attempting this.

Answer 4

I found that this was sufficient to make git and magit work on the home directory.

cd $HOME
echo "gitdir: ./.dotfiles.git" > .git

Then when I'm done using magit to edit the dot files:

rm $HOME/.git

What's the benefit of a nonstandard git directory for the dot files? @tarsius asked. If you use a shell prompt that shows the current git branch you're on, then your entire home directory will look like it's in some git repo and it is in a way. To avoid that confusion of it looking like git is everywhere, it's nice to special case the dot files so that you're not in a git repository everywhere you turn. I usually couple this with an alias to operate on the dot files:

alias homegit="git --work-tree=$HOME --git-dir=$HOME/.dotfiles.git"

But my command line git fu has atrophied from intense magit usage (thank you, @tarsius!) so it's helpful to be able to tend to my dot files with magit.