Subject: Re: bug#39977: 28.0.50; Unhelpful stack trace

From: Eli Zaretskii <[email-masked]>
Date: Sat, 14 Mar 2020 12:10:09 +0200

> Cc: [email-masked], [email-masked]
> From: martin rudalics <[email-masked]>
> Date: Sat, 14 Mar 2020 09:48:20 +0100
> 
>  >> In either case sf = NULL; is not TRT but I think you are aware of
>  >> that.
>  >
>  > No, I don't think I'm aware of that.  It's just a local variable, so
>  > why assigning NULL could not be TRT?
> 
> Because it hides the underlying error.  The abort in SELECTED_FRAME is
> there so we can find its cause and that's why I said you are aware of
> it.  Obviously, we can set it to NULL to avoid an abort when, as in the
> case at hand, we construct the mode line or the frame title.  But in
> general doing such a thing in select_window is not TRT.  At least that's
> what I learned from you.

My understanding of the scenario in this report was that the value of
selected_frame didn't have time to become updated before redisplay
kicked in.  If you think the problem is elsewhere, I'm okay with
leaving this crash in emacs-27 until we understand the cause of that
and fix it elsewhere.  I just hope you will have the solution quickly
enough to not release Emacs 27 with this crash.

Thanks.