Subject: bug#46586: 26.3, 27.1.50; Emacs crash in a backtrace (core) dump (a long standing issue)

From: Eli Zaretskii <[email-masked]>
Date: Thu, 18 Feb 2021 17:00:50 +0200

> From: Andreas Schwab <[email-masked]>
> Cc: 路客 <[email-masked]>,  [email-masked],
>   Stefan Monnier
>  <[email-masked]>
> Date: Thu, 18 Feb 2021 15:45:01 +0100
> 
> On Feb 18 2021, Eli Zaretskii wrote:
> 
> > Does anyone see how to stop this infinite recursion, except by
> > counting recursive invocation levels and bailing out at some arbitrary
> > depth?
> 
> Shouldn't the subst->seen list prevent recursion?

Maybe, but the insertion into the 'seen' list is conditioned on #n=
being in 'completed'.  Or maybe I don't understand the logic of the
code well enough.