My dotspacemacs/user-init ()

.spacemacs.el

  (defun untabify-buffer ()
    (interactive)
    (untabify (point-min) (point-max)))

  (defun indent-buffer ()
    (interactive)
    (indent-region (point-min) (point-max)))

  (defun cleanup-buffer ()
    "Perform a bunch of operations on the whitespace content of a buffer."
    (interactive)
    (indent-buffer)
    (untabify-buffer)
    (delete-trailing-whitespace))

  (defun cleanup-region (beg end)
    "Remove tmux artifacts from region."
    (interactive "r")
    (dolist (re '("\\\\|\.*\n" "\W*|\.*"))
      (replace-regexp re "" nil beg end)))

  (global-set-key (kbd "C-x M-t") 'cleanup-region)
  (global-set-key (kbd "C-c n") 'cleanup-buffer)

  (defun save-some-buffers-silently ()
    (interactive)
    (save-some-buffers '!))
  (global-set-key (kbd "C-x w") 'save-some-buffers-silently)

  (defun check-expansion ()
    (save-excursion
      (if (looking-at "\\_>") t
        (backward-char 1)
        (if (looking-at "\\.") t
          (backward-char 1)
          (if (looking-at "->") t nil)))))

  (defun do-yas-expand ()
    (let ((yas/fallback-behavior 'return-nil))
      (yas/expand)))

  (defun tab-indent-or-complete ()
    (interactive)
    (if (minibufferp)
        (minibuffer-complete)
      (if (or (not yas/minor-mode)
              (null (do-yas-expand)))
          (if (check-expansion)
              (company-complete-common)
            (indent-for-tab-command)))))

  (global-set-key [tab] 'tab-indent-or-complete)