Unify ExclusiveSystemParams with normal SystemParams

crates/bevy_ecs/macros/src/lib.rs

@@ -521,6 +521,10 @@ pub fn derive_system_param(input: TokenStream) -> TokenStream {
                         #(#fields: #field_locals,)*
                     }
                 }
+
+                fn world_access_level() -> #path::system::WorldAccessLevel {
+                    <#fields_alias::<'_, '_, #punctuated_generic_idents> as #path::system::SystemParam>::world_access_level()
+                }
             }
 
             // Safety: Each field is `ReadOnlySystemParam`, so this can only read from the `World`

crates/bevy_ecs/src/removal_detection.rs

@@ -7,7 +7,7 @@ use crate::{
     event::{Event, EventCursor, EventId, EventIterator, EventIteratorWithId, Events},
     prelude::Local,
     storage::SparseSet,
-    system::{ReadOnlySystemParam, SystemMeta, SystemParam},
+    system::{ReadOnlySystemParam, SystemMeta, SystemParam, WorldAccessLevel},
     world::{unsafe_world_cell::UnsafeWorldCell, World},
 };
 
@@ -266,4 +266,8 @@ unsafe impl<'a> SystemParam for &'a RemovedComponentEvents {
     ) -> Self::Item<'w, 's> {
         world.removed_components()
     }
+
+    fn world_access_level() -> WorldAccessLevel {
+        WorldAccessLevel::Shared
+    }
 }

crates/bevy_ecs/src/schedule/set.rs

@@ -12,10 +12,7 @@ pub use bevy_ecs_macros::{ScheduleLabel, SystemSet};
 use crate::{
     define_label,
     intern::Interned,
-    system::{
-        ExclusiveFunctionSystem, ExclusiveSystemParamFunction, FunctionSystem,
-        IsExclusiveFunctionSystem, IsFunctionSystem, SystemParamFunction,
-    },
+    system::{FunctionSystem, IsFunctionSystem, SystemParamFunction},
 };
 
 define_label!(
@@ -200,20 +197,6 @@ where
     }
 }
 
-// exclusive systems
-impl<Marker, F> IntoSystemSet<(IsExclusiveFunctionSystem, Marker)> for F
-where
-    Marker: 'static,
-    F: ExclusiveSystemParamFunction<Marker>,
-{
-    type Set = SystemTypeSet<ExclusiveFunctionSystem<Marker, F>>;
-
-    #[inline]
-    fn into_system_set(self) -> Self::Set {
-        SystemTypeSet::<ExclusiveFunctionSystem<Marker, F>>::new()
-    }
-}
-
 #[cfg(test)]
 mod tests {
     use crate::{

crates/bevy_ecs/src/system/builder.rs

@@ -8,6 +8,7 @@ use crate::{
     resource::Resource,
     system::{
         DynSystemParam, DynSystemParamState, Local, ParamSet, Query, SystemMeta, SystemParam,
+        WorldAccessLevel,
     },
     world::{
         FilteredResources, FilteredResourcesBuilder, FilteredResourcesMut,
@@ -513,6 +514,11 @@ impl<'a> DynParamBuilder<'a> {
     /// Creates a new [`DynParamBuilder`] by wrapping a [`SystemParamBuilder`] of any type.
     /// The built [`DynSystemParam`] can be downcast to `T`.
     pub fn new<T: SystemParam + 'static>(builder: impl SystemParamBuilder<T> + 'a) -> Self {
+        assert_ne!(
+            T::world_access_level(),
+            WorldAccessLevel::Exclusive,
+            "DynSystemParam cannot hold exclusive system parameters"
+        );
         Self(Box::new(|world, meta| {
             DynSystemParamState::new::<T>(builder.build(world, meta))
         }))

crates/bevy_ecs/src/system/commands/mod.rs

@@ -29,7 +29,7 @@ use crate::{
     schedule::ScheduleLabel,
     system::{
         command::HandleError, entity_command::CommandWithEntity, input::SystemInput, Deferred,
-        IntoObserverSystem, IntoSystem, RegisteredSystem, SystemId,
+        IntoObserverSystem, IntoSystem, RegisteredSystem, SystemId, WorldAccessLevel,
     },
     world::{
         command_queue::RawCommandQueue, unsafe_world_cell::UnsafeWorldCell, CommandQueue,
@@ -202,6 +202,10 @@ const _: () = {
                 entities: f1,
             }
         }
+
+        fn world_access_level() -> WorldAccessLevel {
+            <(Deferred<CommandQueue>, &Entities) as bevy_ecs::system::SystemParam>::world_access_level()
+        }
     }
     // SAFETY: Only reads Entities
     unsafe impl<'w, 's> bevy_ecs::system::ReadOnlySystemParam for Commands<'w, 's>