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: Sun, 1 Dec 2019 19:27:09 +0000
> Cc: yyoncho@gmail.com, 38406@debbugs.gnu.org
> From: Alan Mackenzie <acm@muc.de>
> 
> post-self-insert-hook's functions, unusually amongs hooks, interfere with
> its triggering event.  This contrasts with, say, after-change-functions,
> where the functions don't insert into or delete from the buffer, or
> pre-redisplay-functions, where the functions don't try to prevent a
> particular window getting displayed.

You'd be surprised to know what some of those hooks do.  Everything
you say they don't, and then some.  There's nothing we can do to
prevent people from shooting themselves in the foot or hanging
themselves with the rope we provided.  And if you think you are the
only one who needs to harden your code to let people do the craziest
things with these hooks, please don't think so: you are definitely
not alone.

But breaking a hook's contract as a means to teach people not to shoot
themselves in the foot is not right.  If the uses are legitimate, they
should be able to do them; if they aren't, let them cope with the
consequences.

> So to call this hook at the end of c-electric-brace would mean having to
> filter the hook first (at the very least, to remove
> electric-pair-post-self-insert-function), which just seems very hackish
> and unsatisfactory.

It doesn't seem too hackish to me, and as a nice bonus we will have
post-self-insert-hook act as per its contract again.

So could you please do that?  TIA.