Re: backup-buffer-copy loops if old backup can't be deleted

[martin rudalics <rudalics@gmx.at>]

 > The bug occurs when there is a backup file FILE~ for some FILE the user
 > modified and wants to save. If the user doesn't have the privileges to
 > unlink FILE~, it will try over and over again, resulting in an infinite
 > loop. Pressing C-g gets it out of the loop, but the modifications still
 > haven't been saved. Backtraces always mention backup-buffer-copy, I
 > guess that's where the actual loop happens.

I suppose the `file-error' handler of `backup-buffer-copy'

	  (while (condition-case ()
		     (progn
		       (condition-case nil
			   (delete-file to-name)
			 (file-error nil))
		       (copy-file from-name to-name nil t)
		       nil)
		   (file-already-exists t))
	    ;; The file was somehow created by someone else between
	    ;; `delete-file' and `copy-file', so let's try again.
	    nil))

will ignore any error in `delete-file'.  The subsequent `copy-file' will
trigger a `file-already-exists' error and Emacs continues to loop.  In
practice, the `file-already-exists' error is always due to a failure to
delete `to-name' and hardly ever to some strange power creating files in
between.

Likely the `file-error' handler of `backup-buffer' will encounter a
similar fate when `backupname' can't be deleted by `backup-buffer-copy'.