emacs/lisp/emacs-lock.el

;;; emacs-lock.el --- protect buffers against killing or exiting -*- lexical-binding: t -*-

;; Copyright (C) 2011-2018 Free Software Foundation, Inc.

;; Author: Juanma Barranquero <lekktu@gmail.com>
;; Inspired by emacs-lock.el by Tom Wurgler <twurgler@goodyear.com>
;; Maintainer: emacs-devel@gnu.org
;; Keywords: extensions, processes

;; This file is part of GNU Emacs.

;; GNU Emacs is free software: you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation, either version 3 of the License, or
;; (at your option) any later version.

;; GNU Emacs is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;; GNU General Public License for more details.

;; You should have received a copy of the GNU General Public License
;; along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.

;;; Commentary:

;; This package defines a minor mode Emacs Lock to mark a buffer as
;; protected against accidental killing, or exiting Emacs, or both.
;; Buffers associated with inferior modes, like shell or telnet, can
;; be treated specially, by auto-unlocking them if their inferior
;; processes are dead.

;;; Code:

(defgroup emacs-lock nil
  "Emacs-Lock mode."
  :version "24.1"
  :group 'convenience)

(defcustom emacs-lock-default-locking-mode 'all
  "Default locking mode of Emacs-Locked buffers.

Its value is used as the default for `emacs-lock-mode' (which
see) the first time that Emacs Lock mode is turned on in a buffer
without passing an explicit locking mode.

Possible values are:
 exit   -- Emacs cannot exit while the buffer is locked
 kill   -- the buffer cannot be killed, but Emacs can exit as usual
 all    -- the buffer is locked against both actions
 nil    -- the buffer is not locked"
  :type '(choice
          (const :tag "Do not allow Emacs to exit" exit)
          (const :tag "Do not allow killing the buffer" kill)
          (const :tag "Do not allow killing the buffer or exiting Emacs" all)
          (const :tag "Do not lock the buffer" nil))
  :group 'emacs-lock
  :version "24.1")

;; Note: as auto-unlocking can lead to data loss, it would be better
;; to default to nil; but the value below is for compatibility with
;; the old emacs-lock.el.
(defcustom emacs-lock-unlockable-modes '((shell-mode . all)
                                         (telnet-mode . all))
  "Alist of auto-unlockable modes.
Each element is a pair (MAJOR-MODE . ACTION), where ACTION is
one of `kill', `exit' or `all'.  Buffers with matching major
modes are auto-unlocked for the specific action if their
inferior processes are not alive.  If this variable is t, all
buffers associated to inferior processes are auto-unlockable
for both actions (NOT RECOMMENDED)."
  :type '(choice
          (const :tag "All buffers with inferior processes" t)
          (repeat :tag "Selected modes"
           (cons :tag "Set auto-unlock for"
            (symbol :tag "Major mode")
            (radio
             (const :tag "Allow exiting" exit)
             (const :tag "Allow killing" kill)
             (const :tag "Allow both" all)))))
  :group 'emacs-lock
  :version "24.1")

(defcustom emacs-lock-locked-buffer-functions nil
  "Abnormal hook run when Emacs Lock prevents exiting Emacs, or killing a buffer.
The functions get one argument, the first locked buffer found."
  :type 'hook
  :group 'emacs-lock
  :version "24.3")

(defvar-local emacs-lock-mode nil
  "If non-nil, the current buffer is locked.
It can be one of the following values:
 exit   -- Emacs cannot exit while the buffer is locked
 kill   -- the buffer cannot be killed, but Emacs can exit as usual
 all    -- the buffer is locked against both actions
 nil    -- the buffer is not locked

See also `emacs-lock-unlockable-modes', which exempts buffers under
some major modes from being locked under some circumstances.")
(put 'emacs-lock-mode 'permanent-local t)

(defvar-local emacs-lock--old-mode nil
  "Most recent locking mode set on the buffer.
Internal use only.")
(put 'emacs-lock--old-mode 'permanent-local t)

(defvar-local emacs-lock--try-unlocking nil
  "Non-nil if current buffer should be checked for auto-unlocking.
Internal use only.")
(put 'emacs-lock--try-unlocking 'permanent-local t)

(defun emacs-lock-live-process-p (buffer-or-name)
  "Return t if BUFFER-OR-NAME is associated with a live process."
  (process-live-p (get-buffer-process buffer-or-name)))

(defun emacs-lock--can-auto-unlock (action)
  "Return t if the current buffer can auto-unlock for ACTION.
ACTION must be one of `kill' or `exit'.
See `emacs-lock-unlockable-modes'."
  (and emacs-lock--try-unlocking
       (not (emacs-lock-live-process-p (current-buffer)))
       (or (eq emacs-lock-unlockable-modes t)
           (let ((unlock (cdr (assq major-mode emacs-lock-unlockable-modes))))
             (or (eq unlock 'all) (eq unlock action))))))

(defun emacs-lock--exit-locked-buffer ()
  "Return the first exit-locked buffer found."
  (save-current-buffer
    (catch :found
      (dolist (buffer (buffer-list))
        (set-buffer buffer)
        (unless (or (emacs-lock--can-auto-unlock 'exit)
                    (memq emacs-lock-mode '(nil kill)))
          (throw :found buffer)))
      nil)))

(defun emacs-lock--kill-emacs-hook ()
  "Signal an error if any buffer is exit-locked.
Used from `kill-emacs-hook' (which see)."
  (let ((locked (emacs-lock--exit-locked-buffer)))
    (when locked
      (run-hook-with-args 'emacs-lock-locked-buffer-functions locked)
      (error "Emacs cannot exit because buffer %S is locked"
             (buffer-name locked)))))

(defun emacs-lock--kill-emacs-query-functions ()
  "Display a message if any buffer is exit-locked.
Return a value appropriate for `kill-emacs-query-functions' (which see)."
  (let ((locked (emacs-lock--exit-locked-buffer)))
    (if (not locked)
        t
      (run-hook-with-args 'emacs-lock-locked-buffer-functions locked)
      (message "Emacs cannot exit because buffer %S is locked"
               (buffer-name locked))
      nil)))

(defun emacs-lock--kill-buffer-query-functions ()
  "Display a message if the current buffer is kill-locked.
Return a value appropriate for `kill-buffer-query-functions' (which see)."
  (if (or (emacs-lock--can-auto-unlock 'kill)
          (memq emacs-lock-mode '(nil exit)))
      t
    (run-hook-with-args 'emacs-lock-locked-buffer-functions (current-buffer))
    (message "Buffer %S is locked and cannot be killed" (buffer-name))
    nil))

(defun emacs-lock--set-mode (mode arg)
  "Setter function for `emacs-lock-mode'."
  (setq emacs-lock-mode
        (cond ((memq arg '(all exit kill))
               ;; explicit locking mode arg, use it
               arg)
              ((and (eq arg current-prefix-arg) (consp current-prefix-arg))
               ;; called with C-u M-x emacs-lock-mode, so ask the user
               (intern (completing-read "Locking mode: "
                                        '("all" "exit" "kill")
                                        nil t nil nil
                                        (symbol-name
                                         emacs-lock-default-locking-mode))))
              ((eq mode t)
               ;; turn on, so use previous setting, or customized default
               (or emacs-lock--old-mode emacs-lock-default-locking-mode))
              (t
               ;; anything else (turn off)
               mode))))

(define-obsolete-variable-alias 'emacs-lock-from-exiting
  'emacs-lock-mode "24.1")

;;;###autoload
(define-minor-mode emacs-lock-mode
  "Toggle Emacs Lock mode in the current buffer.
If called with a plain prefix argument, ask for the locking mode
to be used.  With any other prefix ARG, turn mode on if ARG is
positive, off otherwise.  If called from Lisp, enable the mode if
ARG is omitted or nil.

Initially, if the user does not pass an explicit locking mode, it
defaults to `emacs-lock-default-locking-mode' (which see);
afterwards, the locking mode most recently set on the buffer is
used instead.

When called from Elisp code, ARG can be any locking mode:

 exit   -- Emacs cannot exit while the buffer is locked
 kill   -- the buffer cannot be killed, but Emacs can exit as usual
 all    -- the buffer is locked against both actions

Other values are interpreted as usual.

See also `emacs-lock-unlockable-modes', which exempts buffers under
some major modes from being locked under some circumstances."
  :init-value nil
  :lighter (""
            (emacs-lock--try-unlocking " locked:" " Locked:")
            (:eval (symbol-name emacs-lock-mode)))
  :group 'emacs-lock
  :variable (emacs-lock-mode .
                             (lambda (mode)
                               (emacs-lock--set-mode mode arg)))
  (when emacs-lock-mode
    (setq emacs-lock--old-mode emacs-lock-mode)
    (setq emacs-lock--try-unlocking
          (and (if (eq emacs-lock-unlockable-modes t)
                   (emacs-lock-live-process-p (current-buffer))
                 (assq major-mode emacs-lock-unlockable-modes))
               t))))

(unless noninteractive
  (add-hook 'kill-buffer-query-functions 'emacs-lock--kill-buffer-query-functions)
  ;; We set a hook in both kill-emacs-hook and kill-emacs-query-functions because
  ;; we really want to use k-e-q-f to stop as soon as possible, but don't want to
  ;; be caught by surprise if someone calls `kill-emacs' instead.
  (add-hook 'kill-emacs-hook 'emacs-lock--kill-emacs-hook)
  (add-hook 'kill-emacs-query-functions 'emacs-lock--kill-emacs-query-functions))

(defun emacs-lock-unload-function ()
  "Unload the Emacs Lock library."
  (catch :continue
    (dolist (buffer (buffer-list))
      (set-buffer buffer)
      (when emacs-lock-mode
        (if (y-or-n-p (format "Buffer %S is locked, unlock it? " (buffer-name)))
            (emacs-lock-mode -1)
          (message "Unloading of feature `emacs-lock' aborted.")
          (throw :continue t))))
    ;; continue standard unloading
    nil))

;;; Compatibility

(defun toggle-emacs-lock ()
  "Toggle `emacs-lock-from-exiting' for the current buffer."
  (declare (obsolete emacs-lock-mode "24.1"))
  (interactive)
  (call-interactively 'emacs-lock-mode))

(provide 'emacs-lock)

;;; emacs-lock.el ends here