bug#55660: 29.0.50; PGTK degrades to terminal-compatible keyboard events

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

Derek Upham <derek_upham@mailfence.com> writes:

> How about this?
>
> ** Keyboard behavior depends on your GTK input method
>
> The GTK3 libraries may interpret and process keypresses as part of the
> current GTK input method, before passing them as input events to
> Emacs.
> GTK applications like PGTK Emacs configure their input method
> automatically based on environment variables, particularly LANG and
> GTK_IM_MODULE.
>
> If you notice differences in keyboard behavior depending on how you
> start PGTK Emacs, compare your environments using
> `process-environment'.
> For example, you may see behavior differences when running Emacs out
> of
> a systemd unit file, compared to running Emacs from the command line.
> Input methods may also cause the keyboard behavior to change if you
> switch from a GTK-based build to a PGTK-based build.
>
> Emacs may reveal bugs that are in the input method libraries. Those
> libraries are out of Emacs's control, but you can tell PGTK Emacs to
> bypass input methods entirely using an Emacs Lisp function:
>
>  M-: (pgtk-use-im-context nil)

No, that doesn't describe the problem very well.  `process-environment'
is certainly completely unrelated, and the description is much more
vague, with no examples of what can go wrong with faulty input methods.

The first half of the entry also describes a different problem, which
has already been in PROBLEMS for a while.