magit-status-dir.el

  (defun $magit-status-in-dir (dir)
    "limit magit status to directory"
    (interactive "D")
    (require 'magit)
    (let* ((root (vc-git-root dir))
           (dir (list (file-relative-name dir root)))
           (magit-status-mode-hook (cons (lambda () (setq-local magit-diff-section-file-args dir))
                                         magit-status-mode-hook)))
      (magit-status-internal root)))

  (defun $magit-status-current-dir ()
    "run magit in current dir"
    (interactive)
    ($magit-status-in-dir default-directory))

  (defun $magit-clear-diff-args-if-not-dir-local ()
    (unless (assq 'magit-diff-section-file-args dir-local-variables-alist)
      (setq-local magit-diff-section-file-args nil)))

  (advice-add 'magit-status :around
              (defun $magit-remove-diff-args (fn &rest args)
                (let ((magit-status-mode-hook (cons '$magit-clear-diff-args-if-not-dir-local
                                                    magit-status-mode-hook)))
                  (apply fn args))))