bug#54289: 29.0.50; Emacs ignores xmodmap Super_L assignment

[Po Lu via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

Stephen Berman <stephen.berman@gmx.net> writes:

> AFAIK Xfce4 uses Gtk3, and e.g. xfce4-terminal and thunar (file manager)
> recognize my Super_L mapping to `/'.  LibreOffice does too.  The only
> other program I use that ignores Super_L is Firefox, but it has since
> long before this Emacs problem started (with your commit 15910e5d
> according to git bisect); I've search the web about this Firefox issue
> but haven't found anything.

Interesting, but please see below.

> Of these, Emacs fails to recognize only the Super_L mapping, since the
> above-mentioned commit.  (As an experiment I added `remove Super_L =
> Mod4' before the Super_L = slash mapping, logged out and back in, but
> the result was that none of the .Xmodmap mappings were recognized, not
> just in Emacs but also e.g. in xfce4-terminal.  So I removed that line
> to restore the status quo ante.)

Can you show the output of running just `xmodmap' without any arguments?
I suspect that some modifier is mapped to Super_L, alongside slash.

That is incorrect, so Emacs and Firefox are within their rights to
ignore such a mapping.

Thanks.