GTK Emacs and input modules

[Yuri Khan <yuri.v.khan@gmail.com>]

Hello,

Can someone please consult me on Emacs’s interaction with GTK input modules?

Steps:

1. $ emacs -Q
2. C-h k C-S-u

Observed: no reaction.

3. C-S-u

Observed: Emacs gets into a state where it ignores any keys except
ESC, 0-9, a-f, A-F, RET, SPC. Pressing any of these keys except RET
takes it out of this state.

4. C-h k C-; (also C-., C-,, C-0, C-1, C-9)

Observed: C-; is undefined. (C-0, C-1, C-9 run the command digit-argument.)

So: things mostly work but C-S-u doesn’t.

Same behavior with $ GTK_IM_MODULE=ibus emacs.

----

1. $ GTK_IM_MODULE=xim emacs
2–4. same

Observed: C-u (translated from C-S-u) runs the command universal-argument.

; runs the command self-insert-command.
. runs the command self-insert-command.
, runs the command self-insert-command.
0 runs the command self-insert-command.
1 runs the command self-insert-command.
9 runs the command self-insert-command.

So: Now C-S-u works but a bunch of other keys lose their Ctrl.

----

If I set GTK_IM_MODULE to pretty much any other value from the list I
get from running
/usr/lib/x86_64-linux-gnu/libgtk-3-0/gtk-query-immodules-3.0, C-S-u
displays an underlined letter ‘u’, then ignores any keys except ESC,
SPC, RET, 0-9, a-f, A-F.

----

How can I get all of C-S-u, C-;, C-., C-, C-0, C-1, C-9 keys in GTK Emacs?

(Of course I want C-S-u for insert-char. No, C-x 8 RET is not an
acceptable alternative because every other application uses
Ctrl+Shift+U and I want consistency across my desktop.)