Moved events to ECS (#1823)

Fixes #1809. It makes it also possible to use `derive` for `SystemParam` inside ECS and avoid manual implementation. An alternative solution to macro changes is to use `use crate as bevy_ecs;` in `event.rs`.

crates/bevy_app/src/app_builder.rs

@@ -1,11 +1,11 @@
 use crate::{
     app::{App, AppExit},
-    event::Events,
     plugin::Plugin,
     CoreStage, PluginGroup, PluginGroupBuilder, StartupStage,
 };
 use bevy_ecs::{
     component::{Component, ComponentDescriptor},
+    event::Events,
     schedule::{
         RunOnce, Schedule, Stage, StageLabel, State, SystemDescriptor, SystemSet, SystemStage,
     },

crates/bevy_app/src/lib.rs

@@ -1,6 +1,5 @@
 mod app;
 mod app_builder;
-mod event;
 mod plugin;
 mod plugin_group;
 mod schedule_runner;
@@ -8,17 +7,15 @@ mod schedule_runner;
 pub use app::*;
 pub use app_builder::*;
 pub use bevy_derive::DynamicPlugin;
-pub use event::*;
+pub use bevy_ecs::event::*;
 pub use plugin::*;
 pub use plugin_group::*;
 pub use schedule_runner::*;
 
 pub mod prelude {
     pub use crate::{
-        app::App,
-        app_builder::AppBuilder,
-        event::{EventReader, EventWriter},
-        CoreStage, DynamicPlugin, Plugin, PluginGroup, StartupStage,
+        app::App, app_builder::AppBuilder, CoreStage, DynamicPlugin, Plugin, PluginGroup,
+        StartupStage,
     };
 }
 

crates/bevy_app/src/schedule_runner.rs

@@ -1,5 +1,6 @@
 use super::{App, AppBuilder};
-use crate::{app::AppExit, event::Events, plugin::Plugin, ManualEventReader};
+use crate::{app::AppExit, plugin::Plugin, ManualEventReader};
+use bevy_ecs::event::Events;
 use bevy_utils::{Duration, Instant};
 
 #[cfg(target_arch = "wasm32")]

crates/bevy_ecs/src/event.rs

@@ -1,4 +1,5 @@
-use bevy_ecs::{
+use crate as bevy_ecs;
+use crate::{
     component::Component,
     system::{Local, Res, ResMut, SystemParam},
 };
@@ -76,7 +77,7 @@ enum State {
 ///
 /// # Example
 /// ```
-/// use bevy_app::Events;
+/// use bevy_ecs::event::Events;
 ///
 /// struct MyEvent {
 ///     value: usize

crates/bevy_ecs/src/lib.rs

@@ -2,6 +2,7 @@ pub mod archetype;
 pub mod bundle;
 pub mod component;
 pub mod entity;
+pub mod event;
 pub mod query;
 #[cfg(feature = "bevy_reflect")]
 pub mod reflect;
@@ -16,6 +17,7 @@ pub mod prelude {
     pub use crate::{
         bundle::Bundle,
         entity::Entity,
+        event::{EventReader, EventWriter},
         query::{Added, ChangeTrackers, Changed, Or, QueryState, With, WithBundle, Without},
         schedule::{
             AmbiguitySetLabel, ExclusiveSystemDescriptorCoercion, ParallelSystemDescriptorCoercion,

crates/bevy_input/src/mouse.rs

@@ -1,6 +1,5 @@
 use crate::{ElementState, Input};
-use bevy_app::prelude::EventReader;
-use bevy_ecs::system::ResMut;
+use bevy_ecs::{event::EventReader, system::ResMut};
 use bevy_math::Vec2;
 
 /// A mouse button input event

crates/bevy_input/src/system.rs

@@ -2,10 +2,8 @@ use crate::{
     keyboard::{KeyCode, KeyboardInput},
     ElementState,
 };
-use bevy_app::{
-    prelude::{EventReader, EventWriter},
-    AppExit,
-};
+use bevy_app::AppExit;
+use bevy_ecs::prelude::{EventReader, EventWriter};
 
 /// Sends the AppExit event whenever the "esc" key is pressed.
 pub fn exit_on_esc_system(

crates/bevy_render/src/camera/camera.rs

@@ -1,8 +1,8 @@
 use super::CameraProjection;
-use bevy_app::prelude::EventReader;
 use bevy_ecs::{
     component::Component,
     entity::Entity,
+    event::EventReader,
     query::Added,
     reflect::ReflectComponent,
     system::{Query, QuerySet, Res},

crates/bevy_render/src/mesh/mesh.rs

@@ -2,11 +2,11 @@ use crate::{
     pipeline::{IndexFormat, PrimitiveTopology, RenderPipelines, VertexFormat},
     renderer::{BufferInfo, BufferUsage, RenderResourceContext, RenderResourceId},
 };
-use bevy_app::prelude::EventReader;
 use bevy_asset::{AssetEvent, Assets, Handle};
 use bevy_core::AsBytes;
 use bevy_ecs::{
     entity::Entity,
+    event::EventReader,
     query::{Changed, With},
     system::{Local, Query, QuerySet, Res},
     world::Mut,

crates/bevy_render/src/texture/texture.rs

@@ -5,9 +5,8 @@ use super::{
 use crate::renderer::{
     RenderResource, RenderResourceContext, RenderResourceId, RenderResourceType,
 };
-use bevy_app::prelude::EventReader;
 use bevy_asset::{AssetEvent, Assets, Handle};
-use bevy_ecs::system::Res;
+use bevy_ecs::{event::EventReader, system::Res};
 use bevy_reflect::TypeUuid;
 use bevy_utils::HashSet;
 use thiserror::Error;