How to query the name of the current branch in an elisp function?

Question

I'd like to know the current branch I'm in (in elisp), is there a generic function that returns the name of the current branch?

From looking into vc-mode mode-line logic it seems this relies on private functionality.

Is there a generic way to access the current branch in Emacs? (Using git but via vc this might work for other version control systems too).

Answer 1

The current GIT branch can be accessed using (car (vc-git-branches)) which always returns the current branch first.

However this uses a relatively slow method which accesses all branches. Currently the most direct way to access this is with a private function:
(vc-git--symbolic-ref (buffer-file-name))

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Note that a VCS agnostic function would be preferred but as far as I know this doesn't exist.

Answer 2

You can issue the git-command git branch --show-current directly with vc-git-command:

(defun git+-branch (&optional buffer)
  "Return Git branch for file of BUFFER.
BUFFER defaults to the current buffer."
  (let ((fn (buffer-file-name (or buffer (current-buffer)))))
    (with-temp-buffer 
      (and (eq (vc-backend fn)
           'Git)
       (eq (vc-git-command t 0 fn "branch" "--show-current") 0)
       (buffer-substring-no-properties (point-min) (line-end-position 0))))))