xkb_state_layout_index_is_active seems broken for XKB_STATE_LAYOUT_DEPRESSED and XKB_STATE_LAYOUT_LATCHED.

[wismill]

If we have 2 layouts and e.g. the following state components:

struct state_components components = {
    .base_group = 0
    .latched_group = 0
    .locked_group = 1
    .group = 1
    // …
};

then we have these counter-intuitive results:

xkb_state_layout_index_is_active(state, 0, XKB_STATE_LAYOUT_DEPRESSED) == 1; // Unexpected
xkb_state_layout_index_is_active(state, 0, XKB_STATE_LAYOUT_LATCHED) == 1; // Unexpected
xkb_state_layout_index_is_active(state, 0, XKB_STATE_LAYOUT_LOCKED) == 0;
xkb_state_layout_index_is_active(state, 0, XKB_STATE_LAYOUT_EFFECTIVE) == 0;

This is because we use indexes an not masks, contrary to modifiers. So here 0 may denotes either an unset value or the result of a sum or an actual index.

We should maybe disallow using XKB_STATE_LAYOUT_DEPRESSED and XKB_STATE_LAYOUT_LATCHED and return a negative value, e.g. -2.