(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.

1 files changed, 27 insertions, 12 deletions

diff --git a/lisp/files.el b/lisp/files.el
index 51fde3fd271..549bd1de8a0 100644
--- 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)