When starting Eclipse for the first time in my Ubuntu 20.04, I got a warning (which actually seem to be 2 warnings)

***WARNING: Detected: GTK_IM_MODULE=xim. This input method is unsupported and can cause graphical issues.

***WARNING: Unset GTK_IM_MODULE or set GTK_IM_MODULE=ibus if flicking is experienced. 

log4j:WARN No appenders could be found for logger (org.eclipse.jgit.internal.storage.file.FileSnapshot).

log4j:WARN Please initialize the log4j system properly.

To deal with the GTK... warning, I googled a bit.
I found here that "Gnome made ibus the default input method" (even if the answer is from 2016, figure below suggests it still applies).
But

$ env | grep -i gtk

GTK_IM_MODULE=xim

GTK_MODULES=gail:atk-bridge

So I wonder where is GTK_IM_MODULE set.
What I tried (with no luck):

$ grep -i gtk ~/.bashrc

$ grep -i gtk ~/.profile 

$ grep -i gtk /etc/profile

$ grep -i -nH gtk /etc/profile.d/*

$ grep -i gtk ~/.xprofile 

$ grep -i gtk ~/.xinputrc 

$ gsettings get org.gnome.desktop.interface gtk-im-module

'gtk-im-context-simple'

(note that as per dconf-editor, the default value is '').

I will next try the suggestion in the warning, Unset GTK_IM_MODULE or set GTK_IM_MODULE=ibus, but I still have the question:

Where are GTK_IM_MODULE and GTK_MODULES set?

When launching im-config I see this

EDIT:

Perhaps ~/.xinputrc is responsible. Its contents:

# im-config(8) generated on Tue, 03 Nov 2020 10:36:11 -0300

run_im xim

# im-config signature: 1f92fadecc95eaeaf5534ec0902b5a9b  -

If this is the cause, why would .xinputrc contain that?

EDIT #2:

I have removed .xinputrc, logged out and in again.
Still

$ env | grep -i gtk

GTK_IM_MODULE=xim

GTK_MODULES=gail:atk-bridge

So it seems .xinputrc was not the culprit.

EDIT #3:

I executed

$ im-config -n ibus

$ im-config -m

default

ibus

ibus



ibus

So I made sure ibus was current (in the second line of the output, I had xim before).
I logged out and in again.
Still

$ env | grep -i gtk

GTK_IM_MODULE=xim

GTK_MODULES=gail:atk-bridge

$ cat .xinputrc 

# im-config(8) generated on Thu, 04 Mar 2021 23:34:26 -0300

run_im ibus

# im-config signature: 3d5777226bbd6243ce412ee4470b8020  -

Plus, launching eclipse still gives the same warning (expected, since the environment variables have the same values).
And the ensuing flicker is still present.

As requested in comments

$ env | grep -E '_IM|XMOD'

GTK_IM_MODULE=xim

QT4_IM_MODULE=xim

XMODIFIERS=@im=none

CLUTTER_IM_MODULE=xim

QT_IM_MODULE=ibus

So it seems .xinputrc was not the culprit.

EDIT #4:

After a reboot

$ im-config -m

default

ibus

ibus



ibus

$ env | grep -E '_IM|XMOD'

XMODIFIERS=@im=ibus

QT_IM_MODULE=ibus

$ env | grep -i gtk

GTK_MODULES=gail:atk-bridge

$ grep -i gtk ~/.profile 

$ grep -i gtk /etc/environment

$ grep -i gtk /etc/environment.d/*

/etc/environment.d/90atk-adaptor.conf:GTK_MODULES=${GTK_MODULES:+$GTK_MODULES:}gail:atk-bridge

Plus, eclipse does not show the warning (as expected), and the flicker is gone.

whether GTK_IM_MODULE was also set in /etc/environment.d/90atk-adaptor.conf, I cannot tell (I would need to try a few things to ascertain that).

Even if not needed:

1. The question about what set GTK_IM_MODULE persists.


2. I will try removing .xinputrc, rebooting, and checking again.