Bug 484439

Workaround: https://github.com/Azq2/alt-shift-kbd-layout-switcher

P.S. In Unity, GNOME, Windows works fine.

Can reproduce on wayland, git build. This only happens when Alt is pressed before Shift.

I can also reproduce this on x11. So I think this is an upstream xkb issue.

(In reply to fanzhuyifan from comment #4)
> I can also reproduce this on x11. So I think this is an upstream xkb issue.

I confirmed that I can also reproduce this on XFCE, with a command like `setxkbmap -layout rs,rs,us,de -variant latin,,dvp, -option 'grp:alt_shift_toggle'`

So please report this issue to xkb.

This is another occurrence of the infamous “need to kick hotkeys on release, not press” (see: https://gitlab.freedesktop.org/xorg/xserver/-/issues/258). This is not a bug per se, but a known limitation of the XKB protocol.

(In reply to Wismill from comment #6)
> This is another occurrence of the infamous “need to kick hotkeys on release,
> not press” (see: https://gitlab.freedesktop.org/xorg/xserver/-/issues/258).
> This is not a bug per se, but a known limitation of the XKB protocol.

With Plasma 6.1 this is no longer a problem - if you stop using the XKB configuration grp:alt_shift_toggle and instead use the KDE "alternative shortcut" that can now be configured to be Alt+Shift. With that configuration the repro looks like this:
1. Set up 2+ input layouts
2. Clear "main shorcuts" and set up "alternative shortcut" to "Alt+Shift".
3. Go to a text editor - hold [Alt]; hold [Shift]; release [Alt]; start typing

Observerd result:
The text is typed using the second layout's 2nd level. For example for me the second layout is Hebrew, whose 2nd level is Latin caps so typing produces uppercase English.

(In reply to Wismill from comment #6)
> This is another occurrence of the infamous “need to kick hotkeys on release,
> not press” (see: https://gitlab.freedesktop.org/xorg/xserver/-/issues/258).
> This is not a bug per se, but a known limitation of the XKB protocol.

Any reasons why broken XCB is still used for layout switching? This can be implemented on the KDE side.

Oh, sorry, I mean XKB, not XCB :)

(In reply to Kirill Zhumarin from comment #8)
> Any reasons why broken XCB is still used for layout switching? This can be
> implemented on the KDE side.

As noted in comment #7, using the xkb configuration is optional and with Plasma 6.1 is no longer necessary to have modifier only layout switching shortcuts.

I believe the XKB configuration is still useful for some users - especially on X11 - so I don't expect support for it in the Plasma keyboard KCM will be removed anytime soon, but if people use the new "alternative shortcut" configuration and find generally better, we may be able to make that the primary configuration and relegate the XKB configuration to a "legacy" status.

The main feature I expect people will still want to use the XKB configuration for is that it can have multiple different shortcuts for laytout switching, and some finer behaviors then just "next layout", "last layout".

(In reply to Oded Arbel from comment #7)
> (In reply to Wismill from comment #6)
> > This is another occurrence of the infamous “need to kick hotkeys on release,
> > not press” (see: https://gitlab.freedesktop.org/xorg/xserver/-/issues/258).
> > This is not a bug per se, but a known limitation of the XKB protocol.
> 
> With Plasma 6.1 this is no longer a problem - if you stop using the XKB
> configuration grp:alt_shift_toggle and instead use the KDE "alternative
> shortcut" that can now be configured to be Alt+Shift. With that
> configuration the repro looks like this:
> 1. Set up 2+ input layouts
> 2. Clear "main shorcuts" and set up "alternative shortcut" to "Alt+Shift".
> 3. Go to a text editor - hold [Alt]; hold [Shift]; release [Alt]; start
> typing
> 
> Observerd result:
> The text is typed using the second layout's 2nd level. For example for me
> the second layout is Hebrew, whose 2nd level is Latin caps so typing
> produces uppercase English.

Still broken. At least on X11.

1. Press `Alt`
2. Press `Shift`
3. Release ONLY `Alt`
4. Try to type text. Typed text is uppercase (ok), BUT layout actually is not changed (bad).

(In reply to Kirill Zhumarin from comment #11)
> (In reply to Oded Arbel from comment #7)
> > (In reply to Wismill from comment #6)
> > > This is another occurrence of the infamous “need to kick hotkeys on release,
> > > not press” (see: https://gitlab.freedesktop.org/xorg/xserver/-/issues/258).
> > > This is not a bug per se, but a known limitation of the XKB protocol.
> > 
> > With Plasma 6.1 this is no longer a problem - if you stop using the XKB
> > configuration grp:alt_shift_toggle and instead use the KDE "alternative
> > shortcut" that can now be configured to be Alt+Shift. With that
> > configuration the repro looks like this:
> > 1. Set up 2+ input layouts
> > 2. Clear "main shorcuts" and set up "alternative shortcut" to "Alt+Shift".
> > 3. Go to a text editor - hold [Alt]; hold [Shift]; release [Alt]; start
> > typing
> > 
> > Observerd result:
> > The text is typed using the second layout's 2nd level. For example for me
> > the second layout is Hebrew, whose 2nd level is Latin caps so typing
> > produces uppercase English.
> 
> Still broken. At least on X11.
> 
> 1. Press `Alt`
> 2. Press `Shift`
> 3. Release ONLY `Alt`
> 4. Try to type text. Typed text is uppercase (ok), BUT layout actually is
> not changed (bad).

It looks like the layout changes when release both Alt and Shift. But it should change immediately after pressing.

(In reply to Kirill Zhumarin from comment #8)
> Any reasons why broken XCB is still used for layout switching? This can be
> implemented on the KDE side.

Going against the protocol is opening a can of worms I am not ready to open. Finding a proper ad-hoc fix in libxkbcommon must ensure to not break anything else. So, the main reason is lack of resource. And forget to have this ever fixed in upstream XOrg, no one cares.

So it is great it is fixed in Plasma 6.1! 👏

(In reply to Kirill Zhumarin from comment #12)
> > Still broken. At least on X11.
> > 
> > 1. Press `Alt`
> > 2. Press `Shift`
> > 3. Release ONLY `Alt`
> > 4. Try to type text. Typed text is uppercase (ok), BUT layout actually is
> > not changed (bad).
> 
> It looks like the layout changes when release both Alt and Shift. But it
> should change immediately after pressing.

The new code in Plasma 6.1 by Yifan Zhu (https://invent.kde.org/plasma/kglobalacceld/-/merge_requests/44) implements modifier-only shortcut activation only when all keys are released withing 200ms of each other. During the discussion around that work, the issue was raised of triggering the shortcut by any key release, and work on that has been submitted for Plasma 6.2 (https://invent.kde.org/plasma/kglobalacceld/-/merge_requests/53).

The whole point of this work is to move away from relying on the KKB behavior (whether directly in X11 or through libxkbcommon in Wayland) and have a more correct behavior just for KDE.

(In reply to Oded Arbel from comment #14)
> During the discussion around that work, the issue was
> raised of triggering the shortcut by any key release, and work on that has
> been submitted for Plasma 6.2
> (https://invent.kde.org/plasma/kglobalacceld/-/merge_requests/53).

Thank you. This is truly what Alt-Shift users need.
I tested the same behavior in windows. It also changes the language when releasing any of the modifiers. And it works as I expected.