Add SendMessage destination

Cargo.toml

@@ -9,6 +9,7 @@ authors = ["Mark Poliakov <mark@alnyan.me>"]
 [dependencies]
 core = { version = "1.0.0", optional = true, package = "rustc-std-workspace-core" }
 compiler_builtins = { version = "0.1", optional = true }
+serde = { version = "1.0.193", features = ["derive"], optional = true }
 
 [features]
 default = []

src/io/mod.rs

@@ -81,6 +81,7 @@ pub enum DeviceRequest {
 // Missing docs: self-explanatory names
 #[allow(missing_docs)]
 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
+#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
 #[repr(C)]
 pub enum KeyboardKey {
     Char(u8),
@@ -101,18 +102,35 @@ pub enum KeyboardKey {
 
 /// Alternative representation for [KeyboardKey]
 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
+#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
 #[repr(transparent)]
 pub struct KeyboardKeyCode(u16);
 
 /// Descibes a single event produced by a keyboard device
 // Missing docs: self-explanatory names
 #[allow(missing_docs)]
+#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
 #[derive(Clone, Copy, Debug)]
 pub enum KeyboardKeyEvent {
     Pressed(KeyboardKey),
     Released(KeyboardKey),
 }
 
+/// Specifies where a message should be delivered on a channel
+#[derive(Clone, Copy, Debug)]
+pub enum MessageDestination {
+    /// Broadcast everywhere, including the sender.
+    ///
+    /// # Note
+    ///
+    /// May cause a feedback loop if the sender is also a subscriber of the channel.
+    All,
+    /// Broadcast everywhere, except the sender
+    AllExceptSelf,
+    /// Send to a specific subscriber ID
+    Specific(u32),
+}
+
 impl KeyboardKey {
     /// Converts [KeyboardKey] to its related [KeyboardKeyCode]
     pub const fn code(self) -> KeyboardKeyCode {
@@ -261,3 +279,24 @@ impl From<u32> for GroupId {
         Self(value)
     }
 }
+
+impl From<MessageDestination> for u64 {
+    fn from(value: MessageDestination) -> Self {
+        match value {
+            MessageDestination::All => u64::MAX,
+            MessageDestination::AllExceptSelf => u64::MAX - 1,
+            MessageDestination::Specific(id) => id as u64,
+        }
+    }
+}
+
+impl From<u64> for MessageDestination {
+    fn from(value: u64) -> Self {
+        match value {
+            0..=const { u32::MAX as u64 } => Self::Specific(value as u32),
+            const { u64::MAX - 1 } => Self::AllExceptSelf,
+            u64::MAX => Self::All,
+            _ => panic!("Unexpected MessageDestination value: {:?}", value),
+        }
+    }
+}

src/lib.rs

@@ -3,9 +3,10 @@
 #![allow(
     clippy::new_without_default,
     clippy::should_implement_trait,
-    clippy::module_inception
+    clippy::module_inception,
+    incomplete_features
 )]
-#![feature(trace_macros, const_trait_impl)]
+#![feature(trace_macros, const_trait_impl, inline_const_pat)]
 #![deny(missing_docs)]
 
 #[cfg(feature = "alloc")]