bug#44018: Don't consider play-sound-file to be a 'safe' function

[Eli Zaretskii]

> From: "Basil L. Contovounesios" <contovob@tcd.ie>
> Cc: Lars Ingebrigtsen <larsi@gnus.org>,  mattiase@acm.org,
>   44018@debbugs.gnu.org
> Date: Mon, 26 Oct 2020 17:05:56 +0000
> 
> > Do you understand why 'message' was removed?  I don't, and couldn't
> > find any discussion on Emacs lists that discussed that; I may have
> > missed something.  I have no idea why 'message' could be unsafe.
> > unsafep.el doesn't provide a high-level definition of what is
> > considered "safe", unfortunately, and was evidently written for SES,
> > so may have some bias due to that context.  Still, it is not clear to
> > me why 'message' was removed.
> 
> FWIW, there's an @ignored section in doc/lispref/functions.texi that I
> guess was intended to provide a higher-level description, but the
> following paragraph is the best it currently manages to do:
> 
>   What is a safe Lisp expression?  Basically, it's an expression that
>   calls only built-in functions with no side effects (or only innocuous
>   ones).  Innocuous side effects include displaying messages and
>   altering non-risky buffer-local variables (but not global variables).

Thanks.  But this seems to say 'message' should be considered safe?

Anyway, if this is the criterion we want to apply, let's document it
in unsafep.el, and let's examine the list there with this definition
in mind.