implement SystemParam for SystemId

crates/bevy_ecs/src/system/system_param.rs

@@ -19,6 +19,8 @@ use std::{
     ops::{Deref, DerefMut},
 };
 
+use super::SystemId;
+
 /// A parameter that can be used in a [`System`](super::System).
 ///
 /// # Derive
@@ -1157,6 +1159,39 @@ impl<'w, 's> SystemParamFetch<'w, 's> for SystemChangeTickState {
     }
 }
 
+/// The [`SystemParamState`] of [`SystemIdState`].
+pub struct SystemIdState;
+
+// SAFE: Only reads internal system state
+unsafe impl ReadOnlySystemParamFetch for SystemIdState {}
+
+impl SystemParam for SystemId {
+    type Fetch = SystemIdState;
+}
+
+unsafe impl SystemParamState for SystemIdState {
+    type Config = ();
+
+    fn init(_world: &mut World, _system_meta: &mut SystemMeta, _config: Self::Config) -> Self {
+        Self {}
+    }
+
+    fn default_config() {}
+}
+
+impl<'w, 's> SystemParamFetch<'w, 's> for SystemIdState {
+    type Item = SystemId;
+
+    unsafe fn get_param(
+        _state: &'s mut Self,
+        system_meta: &SystemMeta,
+        _world: &'w World,
+        _change_tick: u32,
+    ) -> Self::Item {
+        system_meta.id
+    }
+}
+
 macro_rules! impl_system_param_tuple {
     ($($param: ident),*) => {
         impl<$($param: SystemParam),*> SystemParam for ($($param,)*) {