bug#38406: 27.0.50; post-self-insert-hook does not hold its contract in cc-mode derived modes

[Eli Zaretskii <eliz@gnu.org>]

> Date: Thu, 5 Dec 2019 20:17:13 +0000
> Cc: yyoncho@gmail.com, 38406@debbugs.gnu.org
> From: Alan Mackenzie <acm@muc.de>
> 
> > We never provide any "safety nets" for silly hook functions, so we
> > shouldn't do that here as well.  OTOH, if someone puts a function on
> > those hooks which does something legitimate, we should meet their
> > expectations and let those functions run, as the contract says.
> 
> I think that, with my latest patch, that is the case.
> 
> > So I think you shouldn't filter anything from the hook before you run
> > it.
> 
> I thought you were urging me to do precisely that two or three posts ago.
> 
> I just tried taking a particular function off of
> c--unsafe-post-self-insert-hook-functions and enabling electric-pair
> mode.  On typing a brace, electric-pair-mode threw an obscure error.  It
> doesn't make sense to call electric-pair-post-self-insert-function twice
> for one keypress.  That is a good reason for having that function
> filtered out of the hook.

There might be a misunderstanding on my part here.  Could you please
explain how come electric-pair-post-self-insert-function is called
twice if it isn't removed from the hook? where's the second (or the
first) call?

> The root of the problem is the hook post-self-insert-hook.  It is a
> thoroughly bad idea.  The implications of introducing it a few years ago
> weren't thought through.

That might be so, but I think it's too late for removing it now.

> Assuming that removing this hook from Emacs isn't an option, we are
> left with ugly ad-hoc workarounds, such as the patch we're currently
> discussing.

Yes.