bug#66546: 30.0.50; save-buffer to write-protected file without backup fails

[Jens Schmidt]

reopen 66546
thanks

Eli Zaretskii <eliz@gnu.org> writes:

>> Date: Sun, 29 Oct 2023 15:23:26 +0100
>> From: Jens Schmidt <jschmidt4gnu@vodafonemail.de>
>> Cc: 66546@debbugs.gnu.org
>>
>> Thanks for installing.
>> 
>> Would you accept a unit test for these issues?
>
> Sure, addition to the test suite are always welcome.

Please review attached test.  I hope I haven't been overperforming.

Thanks.

>From d8ed8ed8ff4e81b7bbee484a3dade45bc15967db Mon Sep 17 00:00:00 2001
From: Jens Schmidt <jschmidt4gnu@vodafonemail.de>
Date: Wed, 1 Nov 2023 19:56:06 +0100
Subject: [PATCH] ; Add tests for writing to write-protected files with
 save-buffer

* test/lisp/files-tests.el (files-tests--with-yes-or-no-p): Add new
macro.
(files-tests-save-buffer-read-only-file): Add new test to test writing
to write-protected files with `save-buffer'.
---
 test/lisp/files-tests.el | 144 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 144 insertions(+)

diff --git a/test/lisp/files-tests.el b/test/lisp/files-tests.el
index 63ce4dab7eb..50f41cedc9b 100644
--- a/test/lisp/files-tests.el
+++ b/test/lisp/files-tests.el
@@ -1717,6 +1717,150 @@ files-tests--save-some-buffers
             (set-buffer-modified-p nil)
             (kill-buffer buf)))))))
 
+(defmacro files-tests--with-yes-or-no-p (reply &rest body)
+  "Execute BODY, providing replies to `yes-or-no-p' queries.
+REPLY should be a cons (PROMPT . VALUE), and during execution of
+BODY this macro provides VALUE as return value to all
+`yes-or-no-p' calls prompting for PROMPT and nil to all other
+`yes-or-no-p' calls.  After execution of BODY, this macro ensures
+that exactly one `yes-or-no-p' call prompting for PROMPT has been
+executed during execution of BODY."
+  (declare (indent 1) (debug (sexp body)))
+  `(cl-letf*
+       ((reply ,reply)
+        (prompts nil)
+        ((symbol-function 'yes-or-no-p)
+         (lambda (prompt)
+           (let ((reply (cdr (assoc prompt (list reply)))))
+             (push (cons prompt reply) prompts)
+             reply))))
+     ,@body
+     (should (equal prompts (list reply)))))
+
+(ert-deftest files-tests-save-buffer-read-only-file ()
+  "Test writing to write-protected files with `save-buffer'.
+Ensure that the issues from bug#66546 are fixed."
+  (ert-with-temp-directory dir
+    (cl-letf* (;; Define convenience functions.
+               ((symbol-function 'file-contents)
+                (lambda (file)
+                  (if (file-exists-p file)
+                      (condition-case err
+                          (with-temp-buffer
+                            (insert-file-contents file)
+                            (buffer-string))
+                        ((error err)))
+                    'missing)))
+               (signal-write-failed
+                (lambda (&rest _)
+                  (signal 'file-error "Write failed")))
+
+               ;; Sanitize environment.
+               (auto-save-default nil)
+               (backup-enable-predicate nil)
+               (before-save-hook nil)
+               (write-contents-functions nil)
+               (local-write-file-hooks nil)
+               (write-file-functions)
+               (after-save-hook nil)
+
+               ;; Set the name of the game.
+               (base "read-only-test")
+               (file (expand-file-name base dir))
+               (backup (make-backup-file-name file))
+
+               (override-read-only-prompt
+                (format "File %s is write-protected; try to save anyway? "
+                        base)))
+
+      ;; Ensure that set-file-modes renders our test file read-only,
+      ;; otherwise skip this test.  Use `file-writable-p' to test for
+      ;; read-only-ness, because that's what function `save-buffer'
+      ;; uses as well.
+      (with-temp-file file (insert "foo\n"))
+      (skip-unless (file-writable-p file))
+      (set-file-modes file (logand (file-modes file)
+                                   (lognot #o0222)))
+      (skip-unless (not (file-writable-p file)))
+
+      (with-current-buffer (find-file-noselect file)
+        ;; Prepare for tests backing up the file.
+        (setq buffer-read-only nil)
+        (goto-char (point-min))
+        (insert "bar\n")
+
+        ;; Save to read-only file with backup, declining prompt.
+        (files-tests--with-yes-or-no-p
+            (cons override-read-only-prompt nil)
+          (should-error
+           (save-buffer)
+           ;; "Attempt to save to a file that you aren't allowed to write"
+           :type 'error))
+        (should-not buffer-backed-up)
+        (should     (buffer-modified-p))
+        (should-not (file-writable-p file))
+        (should     (equal (file-contents file) "foo\n"))
+        (should     (equal (file-contents backup) 'missing))
+
+        ;; Save to read-only file with backup, accepting prompt,
+        ;; experiencing a write error.
+        (files-tests--with-yes-or-no-p
+            (cons override-read-only-prompt t)
+          (should-error
+           (cl-letf (((symbol-function 'write-region) signal-write-failed))
+             (save-buffer))
+           ;; "Write failed"
+           :type 'file-error))
+        (should-not buffer-backed-up)
+        (should     (buffer-modified-p))
+        (should-not (file-writable-p file))
+        (should     (equal (file-contents file) "foo\n"))
+        (should     (equal (file-contents backup) 'missing))
+
+        ;; Save to read-only file with backup, accepting prompt.
+        (files-tests--with-yes-or-no-p
+            (cons override-read-only-prompt t)
+          (save-buffer))
+        (should     buffer-backed-up)
+        (should-not (buffer-modified-p))
+        (should-not (file-writable-p file))
+        (should-not (file-writable-p backup))
+        (should     (equal (file-contents file) "bar\nfoo\n"))
+        (should     (equal (file-contents backup) "foo\n"))
+
+        ;; Prepare for tests not backing up the file.
+        (setq buffer-backed-up nil)
+        (delete-file backup)
+        (goto-char (point-min))
+        (insert "baz\n")
+
+        ;; Save to read-only file without backup, accepting prompt,
+        ;; experiencing a write error.  This tests that issue B of
+        ;; bug#66546 is fixed.
+        (files-tests--with-yes-or-no-p
+            (cons override-read-only-prompt t)
+          (should-error
+           (cl-letf (((symbol-function 'write-region) signal-write-failed))
+             (save-buffer 0))
+           ;; "Write failed"
+           :type 'file-error))
+        (should-not buffer-backed-up)
+        (should     (buffer-modified-p))
+        (should-not (file-writable-p file))
+        (should     (equal (file-contents file) "bar\nfoo\n"))
+        (should     (equal (file-contents backup) 'missing))
+
+        ;; Save to read-only file without backup, accepting prompt.
+        ;; This tests that issue A of bug#66546 is fixed.
+        (files-tests--with-yes-or-no-p
+            (cons override-read-only-prompt t)
+          (save-buffer 0))
+        (should-not buffer-backed-up)
+        (should-not (buffer-modified-p))
+        (should-not (file-writable-p file))
+        (should     (equal (file-contents file) "baz\nbar\nfoo\n"))
+        (should     (equal (file-contents backup) 'missing))))))
+
 (ert-deftest files-tests-save-some-buffers ()
   "Test `save-some-buffers'.
 Test the 3 cases for the second argument PRED, i.e., nil, t, or
-- 
2.30.2