use collections::HashMap; #[derive(Debug, Hash, PartialEq, Eq)]pub(crate) enum SerialKind {    DataDevice,    InputMethod,    MouseEnter,    MousePress,    KeyPress,} #[derive(Clone, Copy, Debug, Eq, PartialEq)]pub(crate) struct Serial(u32); impl Serial {    pub(super) fn as_raw(self) -> u32 {        self.0    }} #[derive(Clone, Copy, Debug, Eq, PartialEq)]pub(crate) struct SelectionSerial(Serial); impl SelectionSerial {    pub(super) fn as_raw(self) -> u32 {        self.0.as_raw()    }} #[derive(Debug)]/// Helper for tracking of different serial kinds.pub(crate) struct SerialTracker {    serials: HashMap<SerialKind, Serial>,    selection_serial: Option<SelectionSerial>,} impl SerialTracker {    pub fn new() -> Self {        Self {            serials: HashMap::default(),            selection_serial: None,        }    }     pub fn update(&mut self, kind: SerialKind, value: u32) {        let serial = Serial(value);         if matches!(&kind, SerialKind::KeyPress | SerialKind::MousePress) {            self.selection_serial = Some(SelectionSerial(serial));        }         self.serials.insert(kind, serial);    }     /// Returns the latest tracked serial of the provided [`SerialKind`].    ///    /// Returns a serial with a raw value of 0 if the kind has not been tracked.    pub fn get(&self, kind: SerialKind) -> Serial {        self.serials.get(&kind).copied().unwrap_or(Serial(0))    }     pub fn selection_serial(&self) -> Option<SelectionSerial> {        self.selection_serial    }} #[cfg(test)]mod tests {    use super::*;     fn raw_selection_serial(serial_tracker: &SerialTracker) -> Option<u32> {        serial_tracker            .selection_serial()            .map(SelectionSerial::as_raw)    }     #[test]    fn test_selection_serial_ignores_unrelated_serial_kinds() {        let mut serial_tracker = SerialTracker::new();        serial_tracker.update(SerialKind::MousePress, 3783);        serial_tracker.update(SerialKind::InputMethod, 5011);        serial_tracker.update(SerialKind::KeyPress, 3787);        serial_tracker.update(SerialKind::MouseEnter, 6000);        serial_tracker.update(SerialKind::DataDevice, 7000);         assert_eq!(raw_selection_serial(&serial_tracker), Some(3787));    }     #[test]    fn test_selection_serial_uses_mouse_press_without_key_press() {        let mut serial_tracker = SerialTracker::new();        serial_tracker.update(SerialKind::MousePress, 3783);         assert_eq!(raw_selection_serial(&serial_tracker), Some(3783));    }     #[test]    fn test_selection_serial_uses_event_arrival_order_across_rollover() {        let mut serial_tracker = SerialTracker::new();        serial_tracker.update(SerialKind::KeyPress, 0xffff_fff0);        serial_tracker.update(SerialKind::MousePress, 0x0000_0010);         assert_eq!(raw_selection_serial(&serial_tracker), Some(0x0000_0010));    }     #[test]    fn test_selection_serial_is_unavailable_without_eligible_input() {        let mut serial_tracker = SerialTracker::new();         assert_eq!(raw_selection_serial(&serial_tracker), None);         serial_tracker.update(SerialKind::InputMethod, 5011);        serial_tracker.update(SerialKind::MouseEnter, 6000);        serial_tracker.update(SerialKind::DataDevice, 7000);         assert_eq!(raw_selection_serial(&serial_tracker), None);    }     #[test]    fn test_zero_is_a_valid_selection_serial() {        let mut serial_tracker = SerialTracker::new();        serial_tracker.update(SerialKind::KeyPress, 0);         assert_eq!(raw_selection_serial(&serial_tracker), Some(0));    }}