I use this function to get the emacs dev version.


(defun emacs-version-dev (here)
  "Display emacs build info and also save it to the kill-ring.
If HERE is non-nil, also insert the string at point."
  (interactive "P")
  (let ((emacs-build-info
         (concat "Emacs version: " (emacs-version) ","
                 " built using commit " emacs-repository-version ".\n\n"
                 "./configure options:\n  " system-configuration-options "\n\n"
                 "Features:\n  " system-configuration-features "\n")))
    (kill-new emacs-build-info)
    (message emacs-build-info)
    (when here
      (insert emacs-build-info))
    emacs-build-info))

AFAIK there is no definitive way to get the branch name because
branches are ephemeral. But the below hack works for me.

(defvar emacs-git-branch
  (when (and emacs-repository-version
             (file-exists-p source-directory))
    (let ((shell-return
           (replace-regexp-in-string
            "[\n)]" " " ; Replace newline and ) chars with spaces
            (shell-command-to-string
             (concat "cd " source-directory " && "
                     "git branch --contains "
                     emacs-repository-version)))))
      ;; Below regexp is tested for following "git branch --contains" values
      ;; Output for a commit in master branch too
      ;;   "* (HEAD detached at origin/emacs-25)
      ;;     master
      ;;   "
      ;; Output for a commit only in emacs-25 branch
      ;;   "* (HEAD detached at origin/emacs-25)
      ;;   "
      ;; (message "%S" shell-return)
      (string-match ".*[/ ]\\([^ ]+?\\)\\s-*$" shell-return)
      (match-string-no-properties 1 shell-return)))
  "Name of git branch from which the current emacs is built.")

https://github.com/kaushalmodi/.emacs.d/blob/master/setup-files/setup-misc.el



-- 

--
Kaushal Modi