state: add API for updating latched and locked mods & layout in server state

[bluetech]

Up to now, the "server state" xkb_state API only offered one entry point to update the server state - xkb_state_update_key, which reflects the direct keyboard keys state. But some updates come out-of-band from keyboard input events stream, for example, a GUI layout switcher.

The X11 XKB protocol has a request which allows for such updates, XkbLatchLockState, but xkbcommon does not have similar functionality. So server applications ended up using xkb_state_update_state for this, but that's a function intended for client applications, not servers.

Add support for updating the latched & locked state of the mods and layout. Note that the depressed states cannot be updated in this way -- XKB does not expect them to be updated out of band.

Fixes: #310
Signed-off-by: Ran Benita [email protected]

[bluetech]

Design note: libX11 takes the XkbLatchLockState request and splits it to four functions - XkbLockGroup, XkbLockModifiers, XkbLatchGroup, XkbLatchModifiers. This is cleaner than the monster function, but I didn't do it here, because it makes it impossible to do an atomic update while getting the best enum xkb_state_component return mask.

[bluetech]

The latched part will need some work, might drop it if I don't find the time to implement it.

[bam80]

So server applications ended up using xkb_state_update_state for this, but that's a function intended for client applications, not servers.

Could you elaborate on what are negative consequences of this, if it already works? Won't we just add a syntactic sugar expanding the API this way?

[wismill]

I added a fix for the latch group action in #483.

[wismill]

Closing in favor of #521