gistfile1.el

(defun find-git-repos-internal (dir found-dirs)
  (cond ((file-directory-p dir)
	 (or (char-equal ?/ (aref dir(1- (length dir))))
	     (setq dir (file-name-as-directory dir)))
	 (let ((lst (directory-files dir nil nil t))
	       fullname file)
	   (while lst
	     (setq file (car lst))
	     (setq lst (cdr lst))
	     (setq fullname (concat dir file))
	     (cond ((member file '("." "..")))
		   ((file-exists-p (concat fullname "/.git"))
		    (message "Found a git directory at %s" fullname)
		    (message "directories so far: %s" found-dirs)
		    (setq found-dirs (add-to-list 'found-dirs fullname)))
		   (t
		    (find-git-repos-internal fullname found-dirs))))))
	(t
	 (message "Directories: %s" found-dirs)
	 found-dirs)))