(basic-save-buffer-2): If there's an error writing the file,

unrename the backup file if it was just made.
(backup-buffer, basic-save-buffer-2, basic-save-buffer-1)
(basic-save-buffer): Value now has form (MODES . BACKUPNAME)
when a backup was just made by renaming.  Otherwise it's nil.

diff --git a/lisp/files.el b/lisp/files.el
index 51fde3fd271dc6dd85f60153d0f338c2fb4720b6..549bd1de8a0b4485b58e0c9174fa41c5e24f074a 100644 (file)
--- a/lisp/files.el
+++ b/lisp/files.el
@@ -2326,13 +2326,17 @@ Interactively, confirmation is required unless you supply a prefix argument."
 (defun backup-buffer ()
   "Make a backup of the disk file visited by the current buffer, if appropriate.
 This is normally done before saving the buffer the first time.
-If the value is non-nil, it is the result of `file-modes' on the original
-file; this means that the caller, after saving the buffer, should change
-the modes of the new file to agree with the old modes.
 
 A backup may be done by renaming or by copying; see documentation of
 variable `make-backup-files'.  If it's done by renaming, then the file is
-no longer accessible under its old name."
+no longer accessible under its old name.
+
+The value is non-nil after a backup was made by renaming.
+It has the form (MODES . BACKUPNAME).
+MODES is the result of `file-modes' on the original
+file; this means that the caller, after saving the buffer, should change
+the modes of the new file to agree with the old modes.
+BACKUPNAME is the backup file name, which is the old file renamed."
   (if (and make-backup-files (not backup-inhibited)
           (not buffer-backed-up)
           (file-exists-p buffer-file-name)
@@ -2386,7 +2390,8 @@ no longer accessible under its old name."
                             (copy-file real-file-name backupname t t)))
                        ;; rename-file should delete old backup.
                        (rename-file real-file-name backupname t)
-                       (setq setmodes (file-modes backupname)))
+                       (setq setmodes
+                             (cons (file-modes backupname) backupname)))
                    (file-error
                     ;; If trouble writing the backup, write it in ~.
                     (setq backupname (expand-file-name
@@ -2882,7 +2887,7 @@ After saving the buffer, this function runs `after-save-hook'."
                  (nthcdr 10 (file-attributes buffer-file-name)))
            (if setmodes
                (condition-case ()
-                   (set-file-modes buffer-file-name setmodes)
+                   (set-file-modes buffer-file-name (car setmodes))
                  (error nil))))
          ;; If the auto-save file was recent before this command,
          ;; delete it now.
@@ -2895,13 +2900,14 @@ After saving the buffer, this function runs `after-save-hook'."
 ;; This does the "real job" of writing a buffer into its visited file
 ;; and making a backup file.  This is what is normally done
 ;; but inhibited if one of write-file-functions returns non-nil.
-;; It returns a value to store in setmodes.
+;; It returns a value (MODES . BACKUPNAME), like backup-buffer.
 (defun basic-save-buffer-1 ()
   (if save-buffer-coding-system
       (let ((coding-system-for-write save-buffer-coding-system))
        (basic-save-buffer-2))
     (basic-save-buffer-2)))
 
+;; This returns a value (MODES . BACKUPNAME), like backup-buffer.
 (defun basic-save-buffer-2 ()
   (let (tempsetmodes setmodes)
     (if (not (file-writable-p buffer-file-name))
@@ -2960,7 +2966,8 @@ After saving the buffer, this function runs `after-save-hook'."
            ;; Since we have created an entirely new file
            ;; and renamed it, make sure it gets the
            ;; right permission bits set.
-           (setq setmodes (or setmodes (file-modes buffer-file-name)))
+           (setq setmodes (or setmodes (cons (file-modes buffer-file-name)
+                                             buffer-file-name)))
            ;; We succeeded in writing the temp file,
            ;; so rename it.
            (rename-file tempname buffer-file-name t))
@@ -2970,10 +2977,18 @@ After saving the buffer, this function runs `after-save-hook'."
        ;; (setmodes is set) because that says we're superseding.
        (cond ((and tempsetmodes (not setmodes))
               ;; Change the mode back, after writing.
-              (setq setmodes (file-modes buffer-file-name))
-              (set-file-modes buffer-file-name (logior setmodes 128))))
-       (write-region (point-min) (point-max)
-                     buffer-file-name nil t buffer-file-truename)))
+              (setq setmodes (cons (file-modes buffer-file-name) buffer-file-name))
+              (set-file-modes buffer-file-name (logior (car setmodes) 128))))
+       (let (success)
+         (unwind-protect
+             (progn
+               (write-region (point-min) (point-max)
+                             buffer-file-name nil t buffer-file-truename)
+               (setq success t))
+           ;; If we get an error writing the new file, and we made
+           ;; the backup by renaming, undo the backing-up.
+           (and setmodes (not success)
+                (rename-file (cdr setmodes) buffer-file-name))))))
     setmodes))
 
 (defun save-some-buffers (&optional arg pred)