bug#53698: 29.0.50; ibus input method of chinese with rime engine can't work in v27 and ibus candidate menu blink in v29

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

Štěpán Němec <stepnem@gmail.com> writes:

> The problem with that option is that it apparently breaks some key
> modifiers, e.g. with x-gtk-use-native-input non-nil it becomes
> impossible to bind C-S-u (Emacs processes it the same as C-u).

Yes, the problem is the same as on the PGTK port, since both use the
same input method system.

> AFAICT, X input has been broken (or rather, you get to pick: either you
> get working IME (with x-gtk-use-native-input non-nil), or working
> modifier keybindings (with it being nil); but given that
> x-gtk-use-native-input defaults to nil, for many/most people IME will
> just stop working;

It works here for me (Fedora 35, stock GNOME with IBus), but we do want
to fix this problem and keep X input methods working as well as they
used to.

Do you see the same problem in other programs that use XIM, such as
xterm?  If not, try placing:

  Emacs.inputStyle: none

in your X defaults file, and see if that solves the problem.

Most of this is caused by a more fundamental problem: XIM is an obsolete
interface with many limitations; most applications today rely on the
authors of input method frameworks to provide input modules for their
specific toolkit, and as a result the XIM backends for input method
frameworks get very little testing and are buggy.

Unfortunately, since we cannot demand that input method frame developers
provide modules specifically for supporting Emacs, the only choice we
have is between using the legacy interface standard to X (XIM) or the
toolkit's input method system (GTK native input), each with its own
limitations and advantages.

It's a sad situation, but there's nothing we can do.

> also, it's not just IMEs like fcitx or ibus, XkbLayout switching has
> the same problem) since the commit that introduced the option
> (bisected yesterday):
>
> commit d76fb0c11e98
> Author: Po Lu <luangruo@yahoo.com>
> Date:   Sat Jan 8 15:21:51 2022 +0800
>
>     Allow using GTK+ to handle input methods on X

Are you sure that's the commit which introduced this bug, and not one of
the preceeding commits that added features to the XIM support?

I find that hard to believe, since it doesn't touch anything related to
XIM.

Thanks.