System Inputs, Outputs, Chaining, and Registration Ergo

Cargo.toml

@@ -194,6 +194,10 @@ path = "examples/ecs/event.rs"
 name = "startup_system"
 path = "examples/ecs/startup_system.rs"
 
+[[example]]
+name = "system_chaining"
+path = "examples/ecs/system_chaining.rs"
+
 [[example]]
 name = "ecs_guide"
 path = "examples/ecs/ecs_guide.rs"

crates/bevy_app/src/app_builder.rs

@@ -95,81 +95,40 @@ impl AppBuilder {
         self
     }
 
-    pub fn add_system(&mut self, system: Box<dyn System>) -> &mut Self {
+    pub fn add_system<S, Params, IntoS>(&mut self, system: IntoS) -> &mut Self
+    where
+        S: System<Input = (), Output = ()>,
+        IntoS: IntoSystem<Params, S>,
+    {
         self.add_system_to_stage(stage::UPDATE, system)
     }
 
-    pub fn add_systems(&mut self, systems: Vec<Box<dyn System>>) -> &mut Self {
-        self.add_systems_to_stage(stage::UPDATE, systems)
-    }
-
-    pub fn init_system(
-        &mut self,
-        build: impl FnMut(&mut Resources) -> Box<dyn System>,
-    ) -> &mut Self {
-        self.init_system_to_stage(stage::UPDATE, build)
-    }
-
-    pub fn init_system_to_stage(
-        &mut self,
-        stage: &'static str,
-        mut build: impl FnMut(&mut Resources) -> Box<dyn System>,
-    ) -> &mut Self {
-        let system = build(&mut self.app.resources);
-        self.add_system_to_stage(stage, system)
-    }
-
-    pub fn add_startup_system_to_stage(
+    pub fn add_startup_system_to_stage<S, Params, IntoS>(
         &mut self,
         stage_name: &'static str,
-        system: Box<dyn System>,
-    ) -> &mut Self {
+        system: IntoS,
+    ) -> &mut Self
+    where
+        S: System<Input = (), Output = ()>,
+        IntoS: IntoSystem<Params, S>,
+    {
         self.app
             .startup_schedule
             .add_system_to_stage(stage_name, system);
         self
     }
 
-    pub fn add_startup_systems_to_stage(
-        &mut self,
-        stage_name: &'static str,
-        systems: Vec<Box<dyn System>>,
-    ) -> &mut Self {
-        for system in systems {
-            self.app
-                .startup_schedule
-                .add_system_to_stage(stage_name, system);
-        }
-        self
-    }
-
-    pub fn add_startup_system(&mut self, system: Box<dyn System>) -> &mut Self {
+    pub fn add_startup_system<S, Params, IntoS>(&mut self, system: IntoS) -> &mut Self
+    where
+        S: System<Input = (), Output = ()>,
+        IntoS: IntoSystem<Params, S>,
+    {
         self.app
             .startup_schedule
             .add_system_to_stage(startup_stage::STARTUP, system);
         self
     }
 
-    pub fn add_startup_systems(&mut self, systems: Vec<Box<dyn System>>) -> &mut Self {
-        self.add_startup_systems_to_stage(startup_stage::STARTUP, systems)
-    }
-
-    pub fn init_startup_system(
-        &mut self,
-        build: impl FnMut(&mut Resources) -> Box<dyn System>,
-    ) -> &mut Self {
-        self.init_startup_system_to_stage(startup_stage::STARTUP, build)
-    }
-
-    pub fn init_startup_system_to_stage(
-        &mut self,
-        stage: &'static str,
-        mut build: impl FnMut(&mut Resources) -> Box<dyn System>,
-    ) -> &mut Self {
-        let system = build(&mut self.app.resources);
-        self.add_startup_system_to_stage(stage, system)
-    }
-
     pub fn add_default_stages(&mut self) -> &mut Self {
         self.add_startup_stage(startup_stage::PRE_STARTUP)
             .add_startup_stage(startup_stage::STARTUP)
@@ -183,34 +142,31 @@ impl AppBuilder {
             .add_stage(stage::LAST)
     }
 
-    pub fn add_system_to_stage(
+    pub fn add_system_to_stage<S, Params, IntoS>(
         &mut self,
         stage_name: &'static str,
-        system: Box<dyn System>,
-    ) -> &mut Self {
+        system: IntoS,
+    ) -> &mut Self
+    where
+        S: System<Input = (), Output = ()>,
+        IntoS: IntoSystem<Params, S>,
+    {
         self.app.schedule.add_system_to_stage(stage_name, system);
         self
     }
 
-    pub fn add_system_to_stage_front(
+    pub fn add_system_to_stage_front<S, Params, IntoS>(
         &mut self,
         stage_name: &'static str,
-        system: Box<dyn System>,
-    ) -> &mut Self {
+        system: IntoS,
+    ) -> &mut Self
+    where
+        S: System<Input = (), Output = ()>,
+        IntoS: IntoSystem<Params, S>,
+    {
         self.app
             .schedule
-            .add_system_to_stage_front(stage_name, system);
-        self
-    }
-
-    pub fn add_systems_to_stage(
-        &mut self,
-        stage_name: &'static str,
-        systems: Vec<Box<dyn System>>,
-    ) -> &mut Self {
-        for system in systems {
-            self.app.schedule.add_system_to_stage(stage_name, system);
-        }
+            .add_system_to_stage_front(stage_name, system.system());
         self
     }
 
@@ -219,7 +175,7 @@ impl AppBuilder {
         T: Send + Sync + 'static,
     {
         self.add_resource(Events::<T>::default())
-            .add_system_to_stage(stage::EVENT, Events::<T>::update_system.system())
+            .add_system_to_stage(stage::EVENT, Events::<T>::update_system)
     }
 
     /// Adds a resource to the current [App] and overwrites any resource previously added of the same type.

crates/bevy_asset/src/assets.rs

@@ -2,7 +2,7 @@ use crate::{
     update_asset_storage_system, Asset, AssetLoader, AssetServer, Handle, HandleId, RefChange,
 };
 use bevy_app::{prelude::Events, AppBuilder};
-use bevy_ecs::{FromResources, IntoSystem, ResMut};
+use bevy_ecs::{FromResources, ResMut};
 use bevy_type_registry::RegisterType;
 use bevy_utils::HashMap;
 use crossbeam_channel::Sender;
@@ -219,14 +219,8 @@ impl AddAsset for AppBuilder {
 
         self.add_resource(assets)
             .register_component::<Handle<T>>()
-            .add_system_to_stage(
-                super::stage::ASSET_EVENTS,
-                Assets::<T>::asset_event_system.system(),
-            )
-            .add_system_to_stage(
-                crate::stage::LOAD_ASSETS,
-                update_asset_storage_system::<T>.system(),
-            )
+            .add_system_to_stage(super::stage::ASSET_EVENTS, Assets::<T>::asset_event_system)
+            .add_system_to_stage(crate::stage::LOAD_ASSETS, update_asset_storage_system::<T>)
             .add_event::<AssetEvent<T>>()
     }
 

crates/bevy_asset/src/lib.rs

@@ -31,7 +31,6 @@ pub mod prelude {
 }
 
 use bevy_app::{prelude::Plugin, AppBuilder};
-use bevy_ecs::IntoSystem;
 use bevy_type_registry::RegisterType;
 
 /// Adds support for Assets to an App. Assets are typed collections with change tracking, which are added as App Resources.
@@ -80,13 +79,13 @@ impl Plugin for AssetPlugin {
             .register_property::<HandleId>()
             .add_system_to_stage(
                 bevy_app::stage::PRE_UPDATE,
-                asset_server::free_unused_assets_system.system(),
+                asset_server::free_unused_assets_system,
             );
 
         #[cfg(all(
             feature = "filesystem_watcher",
             all(not(target_arch = "wasm32"), not(target_os = "android"))
         ))]
-        app.add_system_to_stage(stage::LOAD_ASSETS, io::filesystem_watcher_system.system());
+        app.add_system_to_stage(stage::LOAD_ASSETS, io::filesystem_watcher_system);
     }
 }

crates/bevy_audio/src/lib.rs

@@ -12,7 +12,6 @@ pub mod prelude {
 
 use bevy_app::prelude::*;
 use bevy_asset::AddAsset;
-use bevy_ecs::IntoThreadLocalSystem;
 
 /// Adds support for audio playback to an App
 #[derive(Default)]
@@ -24,9 +23,6 @@ impl Plugin for AudioPlugin {
             .add_asset::<AudioSource>()
             .init_asset_loader::<Mp3Loader>()
             .init_resource::<Audio<AudioSource>>()
-            .add_system_to_stage(
-                stage::POST_UPDATE,
-                play_queued_audio_system::<AudioSource>.thread_local_system(),
-            );
+            .add_system_to_stage(stage::POST_UPDATE, play_queued_audio_system::<AudioSource>);
     }
 }

crates/bevy_core/src/lib.rs

@@ -15,7 +15,6 @@ pub mod prelude {
 }
 
 use bevy_app::prelude::*;
-use bevy_ecs::prelude::*;
 use bevy_math::{Mat3, Mat4, Quat, Vec2, Vec3};
 use bevy_type_registry::RegisterType;
 
@@ -40,8 +39,8 @@ impl Plugin for CorePlugin {
             .register_property::<Mat4>()
             .register_property::<Quat>()
             .register_property::<Option<String>>()
-            .add_system_to_stage(stage::FIRST, time_system.system())
-            .add_system_to_stage(stage::FIRST, timer_system.system())
-            .add_system_to_stage(stage::PRE_UPDATE, entity_labels_system.system());
+            .add_system_to_stage(stage::FIRST, time_system)
+            .add_system_to_stage(stage::FIRST, timer_system)
+            .add_system_to_stage(stage::PRE_UPDATE, entity_labels_system);
     }
 }

crates/bevy_diagnostic/src/frame_time_diagnostics_plugin.rs

@@ -1,7 +1,7 @@
 use crate::{Diagnostic, DiagnosticId, Diagnostics};
 use bevy_app::prelude::*;
 use bevy_core::Time;
-use bevy_ecs::{IntoSystem, Res, ResMut};
+use bevy_ecs::{Res, ResMut};
 
 /// Adds "frame time" diagnostic to an App, specifically "frame time", "fps" and "frame count"
 #[derive(Default)]
@@ -13,9 +13,9 @@ pub struct FrameTimeDiagnosticsState {
 
 impl Plugin for FrameTimeDiagnosticsPlugin {
     fn build(&self, app: &mut bevy_app::AppBuilder) {
-        app.add_startup_system(Self::setup_system.system())
+        app.add_startup_system(Self::setup_system)
             .add_resource(FrameTimeDiagnosticsState { frame_count: 0.0 })
-            .add_system(Self::diagnostic_system.system());
+            .add_system(Self::diagnostic_system);
     }
 }
 

crates/bevy_diagnostic/src/print_diagnostics_plugin.rs

@@ -1,7 +1,7 @@
 use super::{Diagnostic, DiagnosticId, Diagnostics};
 use bevy_app::prelude::*;
 use bevy_core::{Time, Timer};
-use bevy_ecs::{IntoSystem, Res, ResMut};
+use bevy_ecs::{Res, ResMut};
 use std::time::Duration;
 
 /// An App Plugin that prints diagnostics to the console
@@ -35,12 +35,9 @@ impl Plugin for PrintDiagnosticsPlugin {
         });
 
         if self.debug {
-            app.add_system_to_stage(
-                stage::POST_UPDATE,
-                Self::print_diagnostics_debug_system.system(),
-            );
+            app.add_system_to_stage(stage::POST_UPDATE, Self::print_diagnostics_debug_system);
         } else {
-            app.add_system_to_stage(stage::POST_UPDATE, Self::print_diagnostics_system.system());
+            app.add_system_to_stage(stage::POST_UPDATE, Self::print_diagnostics_system);
         }
     }
 }

crates/bevy_ecs/macros/src/lib.rs

@@ -408,23 +408,24 @@ pub fn derive_system_param(input: TokenStream) -> TokenStream {
     }
 
     let generics = ast.generics;
-    let (impl_generics, ty_generics, _where_clause) = generics.split_for_impl();
+    let (impl_generics, ty_generics, where_clause) = generics.split_for_impl();
 
     let struct_name = &ast.ident;
 
     TokenStream::from(quote! {
-        impl #impl_generics #path::SystemParam for #struct_name#ty_generics {
+        impl #impl_generics #path::SystemParam<()> for #struct_name#ty_generics #where_clause {
             fn init(system_state: &mut #path::SystemState, world: &#path::World, resources: &mut #path::Resources) {
-                #(<#field_types>::init(system_state, world, resources);)*
+                #(<#field_types as SystemParam<()>>::init(system_state, world, resources);)*
             }
 
             unsafe fn get_param(
+                input: &mut Option<()>,
                 system_state: &mut #path::SystemState,
                 world: &#path::World,
                 resources: &#path::Resources,
             ) -> Option<Self> {
                 Some(#struct_name {
-                    #(#fields: <#field_types>::get_param(system_state, world, resources)?,)*
+                    #(#fields: <#field_types as SystemParam<()>>::get_param(input, system_state, world, resources)?,)*
                     #(#ignored_fields: <#ignored_field_types>::default(),)*
                 })
             }

crates/bevy_ecs/src/lib.rs

@@ -14,8 +14,8 @@ pub mod prelude {
     pub use crate::{
         core::WorldBuilderSource,
         resource::{ChangedRes, FromResources, Local, Res, ResMut, Resource, Resources},
-        system::{Commands, IntoSystem, IntoThreadLocalSystem, Query, System},
-        Added, Bundle, Changed, Component, Entity, Mut, Mutated, Or, QuerySet, Ref, RefMut, With,
-        Without, World,
+        system::{Commands, IntoSystem, Query, System},
+        Added, Bundle, Changed, Component, Entity, In, IntoChainSystem, Mut, Mutated, Or, QuerySet,
+        Ref, RefMut, With, Without, World,
     };
 }

crates/bevy_ecs/src/resource/resource_query.rs

@@ -1,10 +1,10 @@
 use super::FromResources;
 use crate::{Resource, ResourceIndex, Resources, SystemId};
-use core::{
+use std::{
+    marker::PhantomData,
     ops::{Deref, DerefMut},
     ptr::NonNull,
 };
-use std::marker::PhantomData;
 
 // TODO: align TypeAccess api with Query::Fetch