bug#65068: 29.1; xkb-interception interaction causes problems with key combinations

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

Alexander Prähauser <alexander.praehauser@gmx.at> writes:

> I'm using the interception-`dual-function-keys`-plugin
>
> https://gitlab.com/interception/linux/plugins/dual-function-keys
>
> for my keyboard layout. In version 28.2 it worked perfectly, but
> now, if I try to use combinations using keys that have
> a dual function, the combination breaks off sending the wrong
> signals. For instance, my CapsLock key has a dual function,
> sending a F15 (XF86Launch5) if tapped and acting as the
> apostrophe-key (AC11 in xkb) if held, which is configured in xkb
> to act as an xkb level 3 modifier.

Which virtual modifier key have you assigned to the apostrophe key?

> However, now when I try to use
> CapsLock for a key combination using a level 3 symbol, for
> instance if I hold Control, then press CapsLock, it seems to send
> simply the apostrophe-key, so that I receive the
> message "C-' is undefined" and the key sequence is broken off. If
> I continue to hold both Control and CapsLock, it seems
> to access level 3 normally though, so that I can still use
> combinations consisting of C-[level 3 character]. If I only want
> to access a level 3 symbol by holding CapsLock, it works normally,
> it seems
> only combinations are affected. While typing this message I
> noticed an even weirder thing: my F-key is configured to
> have "a" on level and "Right" on level 5, and Rightalt is
> configured to act as a level 5 modifier if held, and if I
> press the F key normally or while holding Rightalt this works, but
> if I first hold Control, then Rightalt, then tap the
> F-key, it seems to interpret the result as C-f, even though on no
> xkb-level the F-key is configured to actually send f.
>
> The problem persists if I instead build the latest Emacs-version
> (30.1) from Github

Nit: Emacs is not developed on GitHub, but on Savannah:

  https://git.sv.gnu.org/cgit/emacs.git