bug#56653: 29.0.50; S-SPC is treated as SPC in pgtk

[Visuwesh]

[புதன் ஜூலை 20, 2022] Andrew Tropin wrote:

> Everything below is additionally checked with emacs -Q.
>
> `C-h k M-S-SPC` show M-SPC (translated from M-S-SPC) runs the command
> just-one-space. (works as expected).
>
> `C-h k S-SPC` shows SPC runs the command self-insert-command, but I
> expected to see (traslated from S-SPC).
>
> In non-pgtk emacs28 it works as expected (says translated from S-SPC).

This is a known issue.  From etc/PROBLEMS,

    ** Certain keys such as 'C-S-u' are not reported correctly.

    Some keys with modifiers such as Shift and Control might not be
    reported correctly due to incorrectly written GTK input method
    modules.  This is known to happen to 'C-S-u' and 'C->', which are
    misreported as 'C-u' and '>'.

    To disable the use of GTK input methods, evaluate:

      (pgtk-use-im-context nil)

    This will also cause system input methods and features such as the
    Compose key to stop working.

    On X Windows, users should not use Emacs configured with PGTK, since
    this and many other problems do not exist on the regular X builds.