From mboxrd@z Thu Jan  1 00:00:00 1970
From: Nicolas Goaziou <mail@nicolasgoaziou.fr>
Subject: Re: org-pdfview-open doesn't work anymore
Date: Fri, 05 Feb 2016 18:22:59 +0100
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	(Michael Brand's message of "Fri, 5 Feb 2016 14:45:46 +0100")
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To: Michael Brand <michael.ch.brand@gmail.com>
Cc: Org Mode <emacs-orgmode@gnu.org>, Julien Cubizolles <j.cubizolles@free.fr>

Hello,

Michael Brand <michael.ch.brand@gmail.com> writes:

> +      ;; FIXME: Remove this check when most default installations of
> +      ;; Emacs have at least Org 9.0.
> +      (let ((arglist (help-function-arglist cmd)))
> +	(when (or (memq '&optional arglist)
> +		  (memq '&rest arglist)
> +		  (/= 2 (length arglist)))
> +	  (user-error
> +	   (format
> +	    "%s%s%S"
> +	    "Please see Org News for version 9.0 about `org-file-apps', "
> +	    "this function signature is wrong: "
> +	    cmd))))

I have the feeling there is some over-engineering involved there. 

In any case, instead of relying on `help-function-arglist', I suggest to
use something lightweight:

(condition-case err
    (funcall ...)
  (wrong-number-of-arguments
   (user-error "Please ..."))
  (invalid-function
   (user-error "Please ...")))


Regards,

-- 
Nicolas Goaziou