;;; filelock-tests.el --- test file locking -*- lexical-binding: t; -*-

;; Copyright (C) 2021  Free Software Foundation, Inc.

;; 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 this program.  If not, see <https://www.gnu.org/licenses/>.

;;; Commentary:

;; This file tests code in src/filelock.c and, to some extent, the
;; related code in src/fileio.c.
;;
;; See also (info "(emacs)Interlocking") and (info "(elisp)File Locks")

;;; Code:

(require 'cl-macs)
(require 'ert)
(require 'seq)

(defun filelock-tests--fixture (test-function)
  "Call TEST-FUNCTION under a test fixture.
Create a test directory and a buffer whose `buffer-file-name' and
`buffer-file-truename' are a file within it, then call
TEST-FUNCTION.  Finally, delete the buffer and the test
directory."
  (let* ((temp-dir (make-temp-file "filelock-tests" t))
         (name (concat (file-name-as-directory temp-dir)
                       "userfile"))
         (create-lockfiles t))
    (unwind-protect
        (with-temp-buffer
          (setq buffer-file-name name
                buffer-file-truename name)
          (unwind-protect
              (save-current-buffer
                (funcall test-function))
            ;; Set `buffer-file-truename' nil to prevent unlocking,
            ;; which might prompt the user and/or signal errors.
            (setq buffer-file-name nil
                  buffer-file-truename nil)))
      (delete-directory temp-dir t nil))))

(defun filelock-tests--make-lock-name (file-name)
  "Return the lock file name for FILE-NAME.
Equivalent logic in Emacs proper is implemented in C and
unavailable to Lisp."
  (concat (file-name-directory (expand-file-name file-name))
          ".#"
          (file-name-nondirectory file-name)))

(defun filelock-tests--spoil-lock-file (file-name)
  "Spoil the lock file for FILE-NAME.
Cause Emacs to report errors for various file locking operations
on FILE-NAME going forward.  Create a file that is incompatible
with Emacs' file locking protocol, but uses the same name as
FILE-NAME's lock file.  A directory file is used, which is
portable in practice."
  (make-directory (filelock-tests--make-lock-name file-name)))

(defun filelock-tests--unspoil-lock-file (file-name)
  "Remove the lock file spoiler for FILE-NAME.
See `filelock-tests--spoil-lock-file'."
  (delete-directory (filelock-tests--make-lock-name file-name) t))

(defun filelock-tests--should-be-locked ()
  "Abort the current test if the current buffer is not locked.
Exception: on systems without lock file support, aborts the
current test if the current file is locked (which should never
the case)."
  (if (eq system-type 'ms-dos)
      (should-not (file-locked-p buffer-file-truename))
    (should (file-locked-p buffer-file-truename))))

(ert-deftest filelock-tests-lock-unlock-no-errors ()
  "Check that locking and unlocking works without error."
  (filelock-tests--fixture
   (lambda ()
     (should-not (file-locked-p (buffer-file-name)))

     ;; inserting text should lock the buffer's file.
     (insert "this locks the buffer's file")
     (filelock-tests--should-be-locked)
     (unlock-buffer)
     (set-buffer-modified-p nil)
     (should-not (file-locked-p (buffer-file-name)))

     ;; `set-buffer-modified-p' should lock the buffer's file.
     (set-buffer-modified-p t)
     (filelock-tests--should-be-locked)
     (unlock-buffer)
     (should-not (file-locked-p (buffer-file-name)))

     (should-not (file-locked-p (buffer-file-name))))))

(ert-deftest filelock-tests-lock-spoiled ()
  "Check `lock-buffer' ."
  (skip-unless (not (eq system-type 'ms-dos))) ; no filelock support
  (filelock-tests--fixture
   (lambda ()
     (filelock-tests--spoil-lock-file buffer-file-truename)
     ;; FIXME: errors when locking a file are ignored; should they be?
     (set-buffer-modified-p t)
     (filelock-tests--unspoil-lock-file buffer-file-truename)
     (should-not (file-locked-p buffer-file-truename)))))

(ert-deftest filelock-tests-file-locked-p-spoiled ()
  "Check that `file-locked-p' fails if the lockfile is \"spoiled\"."
  (skip-unless (not (eq system-type 'ms-dos))) ; no filelock support
  (filelock-tests--fixture
   (lambda ()
     (filelock-tests--spoil-lock-file buffer-file-truename)
     (let ((err (should-error (file-locked-p (buffer-file-name)))))
       (should (equal (seq-subseq err 0 2)
                      '(file-error "Testing file lock")))))))

(ert-deftest filelock-tests-unlock-spoiled ()
  "Check that `unlock-buffer' fails if the lockfile is \"spoiled\"."
  (skip-unless (not (eq system-type 'ms-dos))) ; no filelock support
  (filelock-tests--fixture
   (lambda ()
     ;; Set the buffer modified with file locking temporarily
     ;; disabled.
     (let ((create-lockfiles nil))
       (set-buffer-modified-p t))
     (should-not (file-locked-p buffer-file-truename))
     (filelock-tests--spoil-lock-file buffer-file-truename)

     ;; Errors from `unlock-buffer' should call
     ;; `userlock--handle-unlock-error' (bug#46397).
     (let (errors)
       (cl-letf (((symbol-function 'userlock--handle-unlock-error)
                  (lambda (err) (push err errors))))
         (unlock-buffer))
       (should (consp errors))
       (should (equal '(file-error "Unlocking file")
                      (seq-subseq (car errors) 0 2)))
       (should (equal (length errors) 1))))))

(ert-deftest filelock-tests-kill-buffer-spoiled ()
  "Check that `kill-buffer' fails if a lockfile is \"spoiled\"."
  (skip-unless (not (eq system-type 'ms-dos))) ; no filelock support
  (filelock-tests--fixture
   (lambda ()
     ;; Set the buffer modified with file locking temporarily
     ;; disabled.
     (let ((create-lockfiles nil))
       (set-buffer-modified-p t))
     (should-not (file-locked-p buffer-file-truename))
     (filelock-tests--spoil-lock-file buffer-file-truename)

     ;; Kill the current buffer.  Because the buffer is modified Emacs
     ;; will attempt to unlock it.  Temporarily bind `yes-or-no-p' to
     ;; a function that fakes a "yes" answer for the "Buffer modified;
     ;; kill anyway?" prompt.
     ;;
     ;; File errors from unlocking files should call
     ;; `userlock--handle-unlock-error' (bug#46397).
     (let (errors)
       (cl-letf (((symbol-function 'yes-or-no-p)
                  (lambda (&rest _) t))
                 ((symbol-function 'userlock--handle-unlock-error)
                  (lambda (err) (push err errors))))
         (kill-buffer))
       (should (consp errors))
       (should (equal '(file-error "Unlocking file")
                      (seq-subseq (car errors) 0 2)))
       (should (equal (length errors) 1))))))

(provide 'filelock-tests)
;;; filelock-tests.el ends here