AW: Need help with ad-do-it, it loops

[klaus.berndl]

Just an assumption:

I think that ad-do-it already sets the return argument (must be because 
otherwise advices which do jst ad-do-it would not work) and maybe your 
construction

(setq ad-return-value ad-do-it)

causes the loop...at least i never saw such a combination)

Klaus



-----Ursprüngliche Nachricht-----
Von: address@hidden [mailto:address@hidden Im Auftrag von Lennart Borgman
Gesendet: Freitag, 8. Mai 2009 00:16
An: Emacs-Devel devel
Betreff: Need help with ad-do-it, it loops

I have a strange case of looping in MuMaMo/nXhtml. One user (Rémi) has this 
problem on Debian. This happens after starting from "emacs -Q"
and just loading nXhtml and pressing RET in the scratch buffer. The output from 
the debugger says

Debugger entered--Lisp error: (error "Lisp nesting exceeds
`max-lisp-eval-depth'")
  ad-Orig-syntax-ppss-flush-cache(192 192)
  apply(ad-Orig-syntax-ppss-flush-cache 192 192)
  ...
  ad-Orig-syntax-ppss-flush-cache(192 192)
  apply(ad-Orig-syntax-ppss-flush-cache 192 192)
  syntax-ppss-flush-cache(192 192)
  self-insert-command(1)
  newline(nil)
  call-interactively(newline nil nil)



When Rémi set max-lisp-eval-depth to 100000 it loops a bit different:

Debugger entered--Lisp error: (error "Variable binding depth exceeds
max-specpdl-size")
  ad-Orig-syntax-ppss-flush-cache(270 270)
  apply(ad-Orig-syntax-ppss-flush-cache 270 270)
  ...
  ad-Orig-syntax-ppss-flush-cache(270 270)
  apply(ad-Orig-syntax-ppss-flush-cache 270 270)
  syntax-ppss-flush-cache(270 270)
  self-insert-command(1)
  newline(nil)
  call-interactively(newline nil nil)



**** I have this defadvise in mumamo.el (in buffer *Scratch* 
mumamo-multi-major-mode is nil):

(defadvice syntax-ppss-flush-cache (around
                                    mumamo-advice-syntax-ppss-flush-cache
                                    activate
                                    compile
                                    )
  "Support for mumamo.
See the defadvice for `syntax-ppss' for an explanation."
  (if (not mumamo-multi-major-mode)
      ad-do-it
    (let ((pos (ad-get-arg 0)))
      (let* ((chunk-at-pos (when (and (boundp 'mumamo-multi-major-mode)
                                      mumamo-multi-major-mode)
                             (mumamo-find-chunks pos
"syntax-ppss-flush-cache"))))
        (if chunk-at-pos
            (let* ((syntax-ppss-last  (overlay-get chunk-at-pos
'syntax-ppss-last))
                   (syntax-ppss-cache (overlay-get chunk-at-pos
'syntax-ppss-cache)))
              (setq ad-return-value ad-do-it)
              (overlay-put chunk-at-pos 'syntax-ppss-last syntax-ppss-last)
              (overlay-put chunk-at-pos 'syntax-ppss-cache syntax-ppss-cache))
          (setq ad-return-value ad-do-it))))))



I can't understand how this can loop. Any suggestions? Am I perhaps using 
ad-do-it incorrectly? The manual does not explicitly say it returns the value 
from the original function, but my understanding is that it does.

(For more information see https://bugs.launchpad.net/nxhtml/+bug/369800)