bug#54458: 27.2; erc-dcc-get: Re-entering top level after C stack overflow

[Eli Zaretskii]

> From: Mattias Engdegård <mattiase@acm.org>
> Date: Mon, 28 Mar 2022 11:23:09 +0200
> Cc: Eli Zaretskii <eliz@gnu.org>, 54458@debbugs.gnu.org, bandali@gnu.org,
>         jp@neverwas.me
> 
> In Emacs 29 the byte-code engine is more stack-efficient but that just means 
> that bigger files can be transferred without a stack overflow. The bug is 
> still there.

There will always be ways of making Emacs run out of C stack space,
with a sufficiently ... ehm ... sophisticated program.  There's no way
around that, as long as the OS places a limit on the runtime stack.

> Presumably we should add a note to the documentation of process filter 
> functions that they shouldn't be used to send more data to the process.

Yes, please.  With an explicit caveat that it could cause stack
overflow.

> (Not sure what to recommend, an idle timer maybe?)

Yes.  IOW, design change.

> I'm not going to fix this because I don't know ERC very well and wouldn't be 
> able to test it sufficiently, but our ERC maintainers do and can!

Hopefully, yes.