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

[Alan Mackenzie <acm@muc.de>]

Hello, Ivan.

On Sun, Dec 01, 2019 at 17:27:33 +0200, yyoncho wrote:
> Hi Alan

> I am not aware of how exactly smartparens uses post-insert-hook.

In the simplest case, when you type, e.g. "{", it inserts "{}".  In other
cases, when you type "}" onto the existing Rbrace in "{}" it erases one
of the Rbraces.

The problem with this for CC Mode (in c-electric-brace, for example) is
that all these extra and removed characters play havoc with CC Mode's
insertion of auto-newlines and its execution of "clean ups" (e.g.
compacting "}\n    else {"  to  "} else {").

> > Again, how does this binding of post-self-insert-hook to nil in CC
> > Mode affect you?  What is it you're trying to do that this binding
> > makes difficult?

> ATM this change breaks at least 2 packages - lsp-mode and smartparents. I
> am the maintainer of lsp-mode and it uses the hook for 2 things:

> 1. There are keys that are triggering displaying function signature.
> 2. There are keys that are triggering onTypeFormatting which happens
> asynchronously.

Ok, thanks for telling me!

Why are you using post-self-insert-hook for these?  This hook can run in
the middle of a major mode's command, but surely you want them to run
_after_ that command, no?  Why not use post-command-hook here instead?

> Thanks,
> Ivan

-- 
Alan Mackenzie (Nuremberg, Germany).