On X11, use events modifiers to detect state

While there's a separate event to deliver modifiers for keyboard,
unfortunately, it's not even remotely reflects the modifiers state.

Thus use events along side regular modifier updates to correctly
detect the state. Also, apply the modifiers from the regular
key event by converting their state to xkb modifiers state.

Links: https://github.com/alacritty/alacritty/issues/7549
Closes: #3388

src/platform_impl/linux/common/xkb/state.rs

@@ -0,0 +1,189 @@
+//! XKB state.
+
+use std::os::raw::c_char;
+use std::ptr::NonNull;
+
+use smol_str::SmolStr;
+#[cfg(x11_platform)]
+use x11_dl::xlib_xcb::xcb_connection_t;
+use xkbcommon_dl::{
+    self as xkb, xkb_keycode_t, xkb_keysym_t, xkb_layout_index_t, xkb_state, xkb_state_component,
+};
+
+use crate::platform_impl::common::xkb::keymap::XkbKeymap;
+#[cfg(x11_platform)]
+use crate::platform_impl::common::xkb::XKBXH;
+use crate::platform_impl::common::xkb::{make_string_with, XKBH};
+
+#[derive(Debug)]
+pub struct XkbState {
+    state: NonNull<xkb_state>,
+    modifiers: ModifiersState,
+}
+
+impl XkbState {
+    #[cfg(wayland_platform)]
+    pub fn new_wayland(keymap: &XkbKeymap) -> Option<Self> {
+        let state = NonNull::new(unsafe { (XKBH.xkb_state_new)(keymap.as_ptr()) })?;
+        Some(Self::new_inner(state))
+    }
+
+    #[cfg(x11_platform)]
+    pub fn new_x11(xcb: *mut xcb_connection_t, keymap: &XkbKeymap) -> Option<Self> {
+        let state = unsafe {
+            (XKBXH.xkb_x11_state_new_from_device)(keymap.as_ptr(), xcb, keymap._core_keyboard_id)
+        };
+        let state = NonNull::new(state)?;
+        Some(Self::new_inner(state))
+    }
+
+    fn new_inner(state: NonNull<xkb_state>) -> Self {
+        let modifiers = ModifiersState::default();
+        let mut this = Self { state, modifiers };
+        this.reload_modifiers();
+        this
+    }
+
+    pub fn get_one_sym_raw(&mut self, keycode: xkb_keycode_t) -> xkb_keysym_t {
+        unsafe { (XKBH.xkb_state_key_get_one_sym)(self.state.as_ptr(), keycode) }
+    }
+
+    pub fn layout(&mut self, key: xkb_keycode_t) -> xkb_layout_index_t {
+        unsafe { (XKBH.xkb_state_key_get_layout)(self.state.as_ptr(), key) }
+    }
+
+    #[cfg(x11_platform)]
+    pub fn depressed_modifiers(&mut self) -> xkb::xkb_mod_mask_t {
+        unsafe {
+            (XKBH.xkb_state_serialize_mods)(
+                self.state.as_ptr(),
+                xkb_state_component::XKB_STATE_MODS_DEPRESSED,
+            )
+        }
+    }
+
+    #[cfg(x11_platform)]
+    pub fn latched_modifiers(&mut self) -> xkb::xkb_mod_mask_t {
+        unsafe {
+            (XKBH.xkb_state_serialize_mods)(
+                self.state.as_ptr(),
+                xkb_state_component::XKB_STATE_MODS_LATCHED,
+            )
+        }
+    }
+
+    #[cfg(x11_platform)]
+    pub fn locked_modifiers(&mut self) -> xkb::xkb_mod_mask_t {
+        unsafe {
+            (XKBH.xkb_state_serialize_mods)(
+                self.state.as_ptr(),
+                xkb_state_component::XKB_STATE_MODS_LOCKED,
+            )
+        }
+    }
+
+    pub fn get_utf8_raw(
+        &mut self,
+        keycode: xkb_keycode_t,
+        scratch_buffer: &mut Vec<u8>,
+    ) -> Option<SmolStr> {
+        make_string_with(scratch_buffer, |ptr, len| unsafe {
+            (XKBH.xkb_state_key_get_utf8)(self.state.as_ptr(), keycode, ptr, len)
+        })
+    }
+
+    pub fn modifiers(&self) -> ModifiersState {
+        self.modifiers
+    }
+
+    pub fn update_modifiers(
+        &mut self,
+        mods_depressed: u32,
+        mods_latched: u32,
+        mods_locked: u32,
+        depressed_group: u32,
+        latched_group: u32,
+        locked_group: u32,
+    ) {
+        let mask = unsafe {
+            (XKBH.xkb_state_update_mask)(
+                self.state.as_ptr(),
+                mods_depressed,
+                mods_latched,
+                mods_locked,
+                depressed_group,
+                latched_group,
+                locked_group,
+            )
+        };
+
+        if mask.contains(xkb_state_component::XKB_STATE_MODS_EFFECTIVE) {
+            // Effective value of mods have changed, we need to update our state.
+            self.reload_modifiers();
+        }
+    }
+
+    /// Reload the modifiers.
+    fn reload_modifiers(&mut self) {
+        self.modifiers.ctrl = self.mod_name_is_active(xkb::XKB_MOD_NAME_CTRL);
+        self.modifiers.alt = self.mod_name_is_active(xkb::XKB_MOD_NAME_ALT);
+        self.modifiers.shift = self.mod_name_is_active(xkb::XKB_MOD_NAME_SHIFT);
+        self.modifiers.caps_lock = self.mod_name_is_active(xkb::XKB_MOD_NAME_CAPS);
+        self.modifiers.logo = self.mod_name_is_active(xkb::XKB_MOD_NAME_LOGO);
+        self.modifiers.num_lock = self.mod_name_is_active(xkb::XKB_MOD_NAME_NUM);
+    }
+
+    /// Check if the modifier is active within xkb.
+    fn mod_name_is_active(&mut self, name: &[u8]) -> bool {
+        unsafe {
+            (XKBH.xkb_state_mod_name_is_active)(
+                self.state.as_ptr(),
+                name.as_ptr() as *const c_char,
+                xkb_state_component::XKB_STATE_MODS_EFFECTIVE,
+            ) > 0
+        }
+    }
+}
+
+impl Drop for XkbState {
+    fn drop(&mut self) {
+        unsafe {
+            (XKBH.xkb_state_unref)(self.state.as_ptr());
+        }
+    }
+}
+
+/// Represents the current state of the keyboard modifiers
+///
+/// Each field of this struct represents a modifier and is `true` if this modifier is active.
+///
+/// For some modifiers, this means that the key is currently pressed, others are toggled
+/// (like caps lock).
+#[derive(Copy, Clone, Debug, Default, PartialEq, Eq)]
+pub struct ModifiersState {
+    /// The "control" key
+    pub ctrl: bool,
+    /// The "alt" key
+    pub alt: bool,
+    /// The "shift" key
+    pub shift: bool,
+    /// The "Caps lock" key
+    pub caps_lock: bool,
+    /// The "logo" key
+    ///
+    /// Also known as the "windows" key on most keyboards
+    pub logo: bool,
+    /// The "Num lock" key
+    pub num_lock: bool,
+}
+
+impl From<ModifiersState> for crate::keyboard::ModifiersState {
+    fn from(mods: ModifiersState) -> crate::keyboard::ModifiersState {
+        let mut to_mods = crate::keyboard::ModifiersState::empty();
+        to_mods.set(crate::keyboard::ModifiersState::SHIFT, mods.shift);
+        to_mods.set(crate::keyboard::ModifiersState::CONTROL, mods.ctrl);
+        to_mods.set(crate::keyboard::ModifiersState::ALT, mods.alt);
+        to_mods.set(crate::keyboard::ModifiersState::SUPER, mods.logo);
+        to_mods
+    }
+}