GNU bug report logs - #46573
28.0.50; Error when edebugging setting unbound place

Previous Next

Full log

View this message in rfc822 format

From: Stefan Monnier <monnier <at> iro.umontreal.ca>
To: Lars Ingebrigtsen <larsi <at> gnus.org>
Cc: Michael Heerdegen <michael_heerdegen <at> web.de>, Gemini Lasswell <gazally <at> runbox.com>, 46573 <at> debbugs.gnu.org
Subject: bug#46573: 28.0.50; Error when edebugging setting unbound place
Date: Tue, 16 Feb 2021 19:00:45 -0500

>>> (put 'gv-place 'edebug-form-spec '(form)) ;So-called "indirect spec".
>>>
>>> That's certainly not correct for the simplest forms like
>>
>> This has been there since the introduction of `gv`, so I think it
>> *is* correct.  The problem is elsewhere (likely introduced by some of
>> my recent changes to Edebug).
>
> Darn!  I thought I had finally learned how to read edebug specs.  :-/  I
> though `form' meant that it's going to be instrumented?  Hm...  but it's
> `(form)' which means, er, uhm.

Yes, it means Edebug rewrites (setf x 5) to something like:

    (edebug-after (edebug-before 1) 3 (setf (edebug-after 0 2 x) 5))

Whose behavior then depends on the definition of (edebug-after N1 N2 EXP)
as a "place", which is here:

    (put 'edebug-after 'gv-expander
         (lambda (do before index place)
           (gv-letplace (getter setter) place
             (funcall do `(edebug-after ,before ,index ,getter)
                      (lambda (store)
                        `(progn (edebug-after ,before ,index ,getter)
                                ,(funcall setter store)))))))

and indeed, there's the bug, introduced by Gemini's commit
d79cf638f278e50c22feb53d6ba556f5ce9d7853 which does (among various other
things):

    [...]
    * lisp/emacs-lisp/gv.el: Modify edebug-after's gv-expander to
    instrument in the setter as well as the getter.
    [...]

    diff --git a/lisp/emacs-lisp/gv.el b/lisp/emacs-lisp/gv.el
    --- a/lisp/emacs-lisp/gv.el
    +++ b/lisp/emacs-lisp/gv.el
    @@ -302,5 +302,7 @@
     (put 'edebug-after 'gv-expander
          (lambda (do before index place)
            (gv-letplace (getter setter) place
              (funcall do `(edebug-after ,before ,index ,getter)
    -                  setter))))
    +                  (lambda (store)
    +                    `(progn (edebug-after ,before ,index ,getter)
    +                            ,(funcall setter store)))))))

Gemini, how important is it to instrument the setter?  It is definitely
undesirable for Edebug, which you end up seeing the result of
computations which don't take place at all during
un-instrumented execution.  How 'bout using something like

    `(edebug-after ,before ,index ,(funcall setter store))

instead?


        Stefan

Previous Next

GNU bug tracking system
Copyright (C) 1999 Darren O. Benham, 1997,2003 nCipher Corporation Ltd, 1994-97 Ian Jackson.