Emacs: Update git-gutter annotations when staging or unstaging changes in magit-status buffer

Question

I use git-gutter for visualizing changes I make to version-controlled files, and magit for staging/committing/diffing etc.

When working on a project I usually keep a magit-status window open at all times. The problem I have is that when I stage or unstage changes in the magit-status buffer and then switch back to the window showing the file whose status I just updated, the fringe annotations produced by git-gutter are not adjusted automatically. (My current workaround to trigger an update is to hit SPC Backspace followed by C-x C-s to save the file, but that's not very efficient.)

I looked at git-gutter.el, and sure enough it provides a customizable variable called git-gutter:update-hooks which is set to

(after-save-hook after-revert-hook window-configuration-change-hook)

by default. So all I really need to do is add the correct hook to this list and I should be good to go. What's the name of the hook that is run when switching windows? I've looked at various sections of the Elisp manual and haven't been able to find what I am looking for. Alternatively, does magit provide a hook that is run when staging or unstaging changes?

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EDIT:

If you are reading this because you're facing a similar problem: Both of the answers I got below are working solutions! For newer versions of magit, @lunaryorn's solution is short and sweet. @Jordon Biondo's solution requires adding a bit more custom code, but comes with generalizable (!) advice for creating custom hooks and injecting them into existing functionality. So, since I can only accept one answer: Boost your SO karma by rewarding both posters with an upvote :)

Answer 1

Edit: with the latest versions of magit and git-gutter, this no longer requires so much configuration, see lunaryorns answer for a more up to date and simple solution.

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Original Answer:

The switching window method might be a bit overkill since you'll be refreshing more than you need to be.

Magit does not offer before/after stage/unstage hooks, however we can make our own hooks using advice!

You can define two variables for your stage and unstage hooks.

(defvar my-magit-after-stage-hooks nil
  "Hooks to be run after staging one item in magit.")

(defvar my-magit-after-unstage-hooks nil
  "Hooks to be run after unstaging one item in magit.")

There is a nice wrapper function for running hooks: run-hooks we will use function advice to run our custom hooks after magit-stage-item and magit-unstage-item

(defadvice magit-stage-item (after run-my-after-stage-hooks activate)
  "Run `my-magit-after-stage-hooks` after staging an item in magit."
  (when (called-interactively-p 'interactive)
    (run-hooks 'my-magit-after-stage-hooks)))

(defadvice magit-unstage-item (after run-my-after-unstage-hooks activate)
  "Run `my-magit-after-unstage-hooks` after unstaging an item in magit."
  (when (called-interactively-p 'interactive)
    (run-hooks 'my-magit-after-unstage-hooks)))

For our hook we can just iterate over all the buffers, and refresh git-gutter when applicable because we don't know what is staged or unstaged. So We will just refresh the git-gutter display on all visible buffers that are running git-gutter-mode. (If you'd like to do all git-gutter buffers, just remove the get-buffer-window call.)

(defun my-refresh-visible-git-gutter-buffers ()
  "Refresh git-gutter-mode on all visible git-gutter-mode buffers."
  (dolist (buff (buffer-list))
    (with-current-buffer buff
      (when (and git-gutter-mode (get-buffer-window buff))
        (git-gutter-mode t)))))

Finally, just add your hook function to your custom hook!

(add-hook 'my-magit-after-unstage-hooks
          'my-refresh-visible-git-gutter-buffers)
(add-hook 'my-magit-after-stage-hooks
          'my-refresh-visible-git-gutter-buffers)

Ideally we would know what file(s) got staged/unstaged and only refresh those buffers, if you could use around advice on a deeper magit function and get the name of the magit status buffer item you are acting on and refresh only that. But this is a good start!

Answer 2

This is what I needed to do with current magit:

(add-hook 'magit-post-refresh-hook
          #'git-gutter:update-all-windows)