Adopt a Fetch pattern for SystemParams (#1074)

Author: cart

crates/bevy_app/src/app_builder.rs

@@ -24,7 +24,7 @@ impl Default for AppBuilder {
         app_builder
             .add_default_stages()
             .add_event::<AppExit>()
-            .add_system_to_stage(stage::LAST, clear_trackers_system);
+            .add_system_to_stage(stage::LAST, clear_trackers_system.system());
         app_builder
     }
 }
@@ -125,68 +125,48 @@ impl AppBuilder {
         self
     }
 
-    pub fn add_system<S, Params, IntoS>(&mut self, system: IntoS) -> &mut Self
-    where
-        S: System<In = (), Out = ()>,
-        IntoS: IntoSystem<Params, S>,
-    {
+    pub fn add_system<S: System<In = (), Out = ()>>(&mut self, system: S) -> &mut Self {
         self.add_system_to_stage(stage::UPDATE, system)
     }
 
-    pub fn on_state_enter<T: Clone + Resource, S, Params, IntoS>(
+    pub fn on_state_enter<T: Clone + Resource, S: System<In = (), Out = ()>>(
         &mut self,
         stage: &str,
         state: T,
-        system: IntoS,
-    ) -> &mut Self
-    where
-        S: System<In = (), Out = ()>,
-        IntoS: IntoSystem<Params, S>,
-    {
+        system: S,
+    ) -> &mut Self {
         self.stage(stage, |stage: &mut StateStage<T>| {
             stage.on_state_enter(state, system)
         })
     }
 
-    pub fn on_state_update<T: Clone + Resource, S, Params, IntoS>(
+    pub fn on_state_update<T: Clone + Resource, S: System<In = (), Out = ()>>(
         &mut self,
         stage: &str,
         state: T,
-        system: IntoS,
-    ) -> &mut Self
-    where
-        S: System<In = (), Out = ()>,
-        IntoS: IntoSystem<Params, S>,
-    {
+        system: S,
+    ) -> &mut Self {
         self.stage(stage, |stage: &mut StateStage<T>| {
             stage.on_state_update(state, system)
         })
     }
 
-    pub fn on_state_exit<T: Clone + Resource, S, Params, IntoS>(
+    pub fn on_state_exit<T: Clone + Resource, S: System<In = (), Out = ()>>(
         &mut self,
         stage: &str,
         state: T,
-        system: IntoS,
-    ) -> &mut Self
-    where
-        S: System<In = (), Out = ()>,
-        IntoS: IntoSystem<Params, S>,
-    {
+        system: S,
+    ) -> &mut Self {
         self.stage(stage, |stage: &mut StateStage<T>| {
             stage.on_state_exit(state, system)
         })
     }
 
-    pub fn add_startup_system_to_stage<S, Params, IntoS>(
+    pub fn add_startup_system_to_stage<S: System<In = (), Out = ()>>(
         &mut self,
         stage_name: &'static str,
-        system: IntoS,
-    ) -> &mut Self
-    where
-        S: System<In = (), Out = ()>,
-        IntoS: IntoSystem<Params, S>,
-    {
+        system: S,
+    ) -> &mut Self {
         self.app
             .schedule
             .stage(stage::STARTUP, |schedule: &mut Schedule| {
@@ -195,11 +175,7 @@ impl AppBuilder {
         self
     }
 
-    pub fn add_startup_system<S, Params, IntoS>(&mut self, system: IntoS) -> &mut Self
-    where
-        S: System<In = (), Out = ()>,
-        IntoS: IntoSystem<Params, S>,
-    {
+    pub fn add_startup_system<S: System<In = (), Out = ()>>(&mut self, system: S) -> &mut Self {
         self.add_startup_system_to_stage(startup_stage::STARTUP, system)
     }
 
@@ -221,15 +197,11 @@ impl AppBuilder {
         .add_stage(stage::LAST, SystemStage::parallel())
     }
 
-    pub fn add_system_to_stage<S, Params, IntoS>(
+    pub fn add_system_to_stage<S: System<In = (), Out = ()>>(
         &mut self,
         stage_name: &'static str,
-        system: IntoS,
-    ) -> &mut Self
-    where
-        S: System<In = (), Out = ()>,
-        IntoS: IntoSystem<Params, S>,
-    {
+        system: S,
+    ) -> &mut Self {
         self.app.schedule.add_system_to_stage(stage_name, system);
         self
     }
@@ -239,7 +211,7 @@ impl AppBuilder {
         T: Send + Sync + 'static,
     {
         self.add_resource(Events::<T>::default())
-            .add_system_to_stage(stage::EVENT, Events::<T>::update_system)
+            .add_system_to_stage(stage::EVENT, Events::<T>::update_system.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, ResMut};
+use bevy_ecs::{FromResources, IntoSystem, ResMut};
 use bevy_reflect::RegisterTypeBuilder;
 use bevy_utils::HashMap;
 use crossbeam_channel::Sender;
@@ -218,8 +218,14 @@ impl AddAsset for AppBuilder {
         };
 
         self.add_resource(assets)
-            .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_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(),
+            )
             .register_type::<Handle<T>>()
             .add_event::<AssetEvent<T>>()
     }

crates/bevy_asset/src/lib.rs

@@ -13,7 +13,7 @@ mod path;
 
 pub use asset_server::*;
 pub use assets::*;
-use bevy_ecs::SystemStage;
+use bevy_ecs::{IntoSystem, SystemStage};
 use bevy_reflect::RegisterTypeBuilder;
 use bevy_tasks::IoTaskPool;
 pub use handle::*;
@@ -88,13 +88,13 @@ impl Plugin for AssetPlugin {
         .register_type::<HandleId>()
         .add_system_to_stage(
             bevy_app::stage::PRE_UPDATE,
-            asset_server::free_unused_assets_system,
+            asset_server::free_unused_assets_system.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);
+        app.add_system_to_stage(stage::LOAD_ASSETS, io::filesystem_watcher_system.system());
     }
 }

crates/bevy_audio/src/lib.rs

@@ -12,6 +12,7 @@ pub mod prelude {
 
 use bevy_app::prelude::*;
 use bevy_asset::AddAsset;
+use bevy_ecs::IntoSystem;
 
 /// Adds support for audio playback to an App
 #[derive(Default)]
@@ -23,6 +24,9 @@ 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>);
+            .add_system_to_stage(
+                stage::POST_UPDATE,
+                play_queued_audio_system::<AudioSource>.system(),
+            );
     }
 }

crates/bevy_core/src/lib.rs

@@ -6,6 +6,7 @@ mod time;
 
 use std::ops::Range;
 
+use bevy_ecs::IntoSystem;
 use bevy_reflect::RegisterTypeBuilder;
 pub use bytes::*;
 pub use float_ord::*;
@@ -37,7 +38,7 @@ impl Plugin for CorePlugin {
             .register_type::<Option<String>>()
             .register_type::<Range<f32>>()
             .register_type::<Timer>()
-            .add_system_to_stage(stage::FIRST, time_system)
-            .add_system_to_stage(stage::PRE_UPDATE, entity_labels_system);
+            .add_system_to_stage(stage::FIRST, time_system.system())
+            .add_system_to_stage(stage::PRE_UPDATE, entity_labels_system.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::{Res, ResMut};
+use bevy_ecs::{IntoSystem, 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)
+        app.add_startup_system(Self::setup_system.system())
             .add_resource(FrameTimeDiagnosticsState { frame_count: 0.0 })
-            .add_system(Self::diagnostic_system);
+            .add_system(Self::diagnostic_system.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::{Res, ResMut};
+use bevy_ecs::{IntoSystem, Res, ResMut};
 use bevy_utils::Duration;
 
 /// An App Plugin that prints diagnostics to the console
@@ -35,9 +35,12 @@ impl Plugin for PrintDiagnosticsPlugin {
         });
 
         if self.debug {
-            app.add_system_to_stage(stage::POST_UPDATE, Self::print_diagnostics_debug_system);
+            app.add_system_to_stage(
+                stage::POST_UPDATE,
+                Self::print_diagnostics_debug_system.system(),
+            );
         } else {
-            app.add_system_to_stage(stage::POST_UPDATE, Self::print_diagnostics_system);
+            app.add_system_to_stage(stage::POST_UPDATE, Self::print_diagnostics_system.system());
         }
     }
 }

crates/bevy_ecs/macros/src/lib.rs

@@ -411,21 +411,27 @@ pub fn derive_system_param(input: TokenStream) -> TokenStream {
     let (impl_generics, ty_generics, where_clause) = generics.split_for_impl();
 
     let struct_name = &ast.ident;
+    let fetch_struct_name = Ident::new(&format!("Fetch{}", struct_name), Span::call_site());
 
     TokenStream::from(quote! {
-        impl #impl_generics #path::SystemParam<()> for #struct_name#ty_generics #where_clause {
+        pub struct #fetch_struct_name;
+        impl #impl_generics #path::SystemParam for #struct_name#ty_generics #where_clause {
+            type Fetch = #fetch_struct_name;
+        }
+
+        impl #impl_generics #path::FetchSystemParam<'a> for #fetch_struct_name {
+            type Item = #struct_name#ty_generics;
             fn init(system_state: &mut #path::SystemState, world: &#path::World, resources: &mut #path::Resources) {
-                #(<#field_types as SystemParam<()>>::init(system_state, world, resources);)*
+                #(<<#field_types as SystemParam>::Fetch as #path::FetchSystemParam>::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> {
+                system_state: &'a #path::SystemState,
+                world: &'a #path::World,
+                resources: &'a #path::Resources,
+            ) -> Option<Self::Item> {
                 Some(#struct_name {
-                    #(#fields: <#field_types as SystemParam<()>>::get_param(input, system_state, world, resources)?,)*
+                    #(#fields: <<#field_types as SystemParam>::Fetch as #path::FetchSystemParam>::get_param(system_state, world, resources)?,)*
                     #(#ignored_fields: <#ignored_field_types>::default(),)*
                 })
             }