Re: tramp (2.0.25); saving remote buffer fails

[Kai Großjohann]

"clemens fischer" <address@hidden> writes:

> address@hidden (Kai Grojohann):
>
>> "Clemens Fischer" <address@hidden> writes:
>>
>>> Debugger entered--Lisp error: (wrong-type-argument number-or-marker-p nil)
>>>   logand(nil 3072)
>>>   byte-code("
>>
>> Could you produce another backtrace with more Lisp and less
>> bytecode?  The solution is to look below the bytecode to find the
>> function that was called, then to find the *.el file containing this
>> function, and to load that with M-x load-library RET.  Repeat if the
>> new backtrace still has bytecode.
>
> here we go:
>
> Debugger entered--Lisp error: (wrong-type-argument number-or-marker-p nil)
>   logand(nil 3072)
>   (< 0 (logand modes 3072))
>   (or file-precious-flag backup-by-copying (< 0 (logand modes 3072)) (and 
> backup-by-copying-when-linked (> ... 1)) (and (or 
> backup-by-copying-when-mismatch ...) (let ... ...)))
>   (if (or file-precious-flag backup-by-copying (< 0 ...) (and 
> backup-by-copying-when-linked ...) (and ... ...)) (backup-buffer-copy 
> real-file-name backupname modes) (rename-file real-file-name backupname t) 
> (setq setmodes (cons modes backupname)))
>   (condition-case nil (if (or file-precious-flag backup-by-copying ... ... 
> ...) (backup-buffer-copy real-file-name backupname modes) (rename-file 
> real-file-name backupname t) (setq setmodes ...)) (file-error (setq 
> backupname ...) (message "Cannot write backup file; backing up in %s" ...) 
> (sleep-for 1) (backup-buffer-copy real-file-name backupname modes)))
>   (let ((delete-old-versions ...) (modes ...)) (condition-case nil (if ... 
> ... ... ...) (file-error ... ... ... ...)) (setq buffer-backed-up t) (if 
> delete-old-versions (while targets ... ...)) setmodes)
>   (condition-case nil (let (... ...) (condition-case nil ... ...) (setq 
> buffer-backed-up t) (if delete-old-versions ...) setmodes) (file-error nil))
>   (if backup-info (condition-case nil (let ... ... ... ... setmodes) 
> (file-error nil)))
>   (let ((real-file-name buffer-file-name) backup-info backupname targets 
> setmodes) (setq real-file-name (file-chase-links real-file-name)) (setq 
> backup-info (find-backup-file-name real-file-name) backupname (car 
> backup-info) targets (cdr backup-info)) (if backup-info (condition-case nil 
> ... ...)))
>   (if (and make-backup-files (not backup-inhibited) (not buffer-backed-up) 
> (file-exists-p buffer-file-name) (memq ... ...)) (let (... backup-info 
> backupname targets setmodes) (setq real-file-name ...) (setq backup-info ... 
> backupname ... targets ...) (if backup-info ...)))
>   backup-buffer()

Hm.  So `modes' was nil.  But why?  The critical part is here:

                (let ((delete-old-versions
                       ;; If have old versions to maybe delete,
                       ;; ask the user to confirm now, before doing anything.
                       ;; But don't actually delete til later.
                       (and targets
                            (or (eq delete-old-versions t) (eq 
delete-old-versions nil))
                            (or delete-old-versions
                                (y-or-n-p (format "Delete excess backup 
versions of %s? "
                                                  real-file-name)))))
                      (modes (file-modes buffer-file-name)))  <--- HERE
                  ;; Actually write the back up file.
                  (condition-case ()
                      (if (or file-precious-flag


See how `modes' is set?  Well, I wonder how that happens.  So please
try this: position point inside that function and do M-x edebug-defun
RET.  Now do whatever produced the error.  The debugger will show you
the source code with an `=>' arrow indicating the current line.  Now
you can use SPC to single-step execution.  As it evals an expression,
the echo area will show the result.

I'm interested in two questions: (1) What is the value of
buffer-file-name, and (2) what is the return value of (file-modes
buffer-file-name)?

I think that (2) will be nil.  But how does that come about?
tramp-handle-file-modes should have been invoked, one could trace it
with M-x edebug-defun RET, as before.

Hm.  Maybe ange-ftp doesn't implement file-modes?  Maybe that's the
reason?  Yeah, that's possible.  Oh, boy.

So maybe what should REALLY happen is that Tramp supports the
operation find-backup-file-name and that tramp-ftp.el invokes
ange-ftp correctly.  But I don't grok this sufficiently well.

Maybe I should install an ftp server and then try to test it myself.

Can you give me the values of all variables that have something to do
with backup?  M-x apropos-variable RET backup RET should provide a
list.

Sorry for taking so long to respond.  I was really really swamped.
-- 
Ambibibentists unite!