bug#34196: Error in auto-revert-buffers: Wrong type argument

[Alex Branham]

On Wed 13 Feb 2019 at 17:09, Michael Albinus <michael.albinus@gmx.de> wrote:

> Thanks for the report. We could apply your patch of course, but I'm
> curious: `default-directory' shall always be set. So I would like to
> know where the error comes from.
>
> Could you, pls, set `debug-on-error' to t, and rerun the test? There
> should be a backtrace, which might tell us more.

I'm not really sure when/how/why default-directory becomes nil. It seems
to happen in non-file-visiting buffers (e.g. *scratch*, *Backtrace*, any
comint buffer, etc) from time to time. I know "from time to time" is
vague; I've had a hard time tracking it down.

I'm using EXWM (not sure if that has anything at all to do with it) and
it seems like it happens when my screen turns off after a period of
inactivity. I'm not really sure how/why Emacs would know about that
though, so perhaps it's totally unrelated.

Thanks,
Alex