Move Resource trait to its own file (#17469)

# Objective

`bevy_ecs`'s `system` module is something of a grab bag, and *very*
large. This is particularly true for the `system_param` module, which is
more than 2k lines long!

While it could be defensible to put `Res` and `ResMut` there (lol no
they're in change_detection.rs, obviously), it doesn't make any sense to
put the `Resource` trait there. This is confusing to navigate (and
painful to work on and review).

## Solution

- Create a root level `bevy_ecs/resource.rs` module to mirror
`bevy_ecs/component.rs`
- move the `Resource` trait to that module
- move the `Resource` derive macro to that module as well (Rust really
likes when you pun on the names of the derive macro and trait and put
them in the same path)
- fix all of the imports

## Notes to reviewers

- We could probably move more stuff into here, but I wanted to keep this
PR as small as possible given the absurd level of import changes.
- This PR is ground work for my upcoming attempts to store resource data
on components (resources-as-entities). Splitting this code out will make
the work and review a bit easier, and is the sort of overdue refactor
that's good to do as part of more meaningful work.

## Testing

cargo build works!

## Migration Guide

`bevy_ecs::system::Resource` has been moved to
`bevy_ecs::resource::Resource`.

crates/bevy_a11y/src/lib.rs

@@ -23,8 +23,8 @@ use bevy_app::Plugin;
 use bevy_derive::{Deref, DerefMut};
 use bevy_ecs::{
     prelude::{Component, Event},
+    resource::Resource,
     schedule::SystemSet,
-    system::Resource,
 };
 
 /// Wrapper struct for [`accesskit::ActionRequest`]. Required to allow it to be used as an `Event`.

crates/bevy_animation/src/graph.rs

@@ -14,7 +14,8 @@ use bevy_ecs::{
     component::Component,
     event::EventReader,
     reflect::ReflectComponent,
-    system::{Res, ResMut, Resource},
+    resource::Resource,
+    system::{Res, ResMut},
 };
 use bevy_reflect::{prelude::ReflectDefault, Reflect, ReflectSerialize};
 use bevy_utils::HashMap;

crates/bevy_app/src/app.rs

@@ -1423,8 +1423,9 @@ mod tests {
         event::{Event, EventWriter, Events},
         query::With,
         removal_detection::RemovedComponents,
+        resource::Resource,
         schedule::{IntoSystemConfigs, ScheduleLabel},
-        system::{Commands, Query, Resource},
+        system::{Commands, Query},
         world::{FromWorld, World},
     };
 

crates/bevy_app/src/main_schedule.rs

@@ -1,11 +1,12 @@
 use crate::{App, Plugin};
 use alloc::{vec, vec::Vec};
 use bevy_ecs::{
+    resource::Resource,
     schedule::{
         ExecutorKind, InternedScheduleLabel, IntoSystemSetConfigs, Schedule, ScheduleLabel,
         SystemSet,
     },
-    system::{Local, Resource},
+    system::Local,
     world::{Mut, World},
 };
 

crates/bevy_app/src/plugin_group.rs

@@ -226,7 +226,7 @@ impl PluginGroup for PluginGroupBuilder {
 
 /// Facilitates the creation and configuration of a [`PluginGroup`].
 ///
-/// Provides a build ordering to ensure that [`Plugin`]s which produce/require a [`Resource`](bevy_ecs::system::Resource)
+/// Provides a build ordering to ensure that [`Plugin`]s which produce/require a [`Resource`](bevy_ecs::resource::Resource)
 /// are built before/after dependent/depending [`Plugin`]s. [`Plugin`]s inside the group
 /// can be disabled, enabled or reordered.
 pub struct PluginGroupBuilder {

crates/bevy_asset/src/asset_changed.rs

@@ -298,7 +298,8 @@ mod tests {
     use bevy_ecs::{
         component::Component,
         event::EventWriter,
-        system::{Commands, IntoSystem, Local, Query, Res, ResMut, Resource},
+        resource::Resource,
+        system::{Commands, IntoSystem, Local, Query, Res, ResMut},
     };
     use bevy_reflect::TypePath;
 

crates/bevy_asset/src/assets.rs

@@ -6,7 +6,8 @@ use crate::{
 use alloc::{sync::Arc, vec::Vec};
 use bevy_ecs::{
     prelude::EventWriter,
-    system::{Res, ResMut, Resource, SystemChangeTick},
+    resource::Resource,
+    system::{Res, ResMut, SystemChangeTick},
 };
 use bevy_reflect::{Reflect, TypePath};
 use bevy_utils::HashMap;

crates/bevy_asset/src/io/embedded/mod.rs

@@ -9,7 +9,7 @@ use crate::io::{
     AssetSource, AssetSourceBuilders,
 };
 use alloc::boxed::Box;
-use bevy_ecs::system::Resource;
+use bevy_ecs::resource::Resource;
 use std::path::{Path, PathBuf};
 
 #[cfg(feature = "embedded_watcher")]

crates/bevy_asset/src/io/source.rs

@@ -8,7 +8,7 @@ use alloc::{
     sync::Arc,
 };
 use atomicow::CowArc;
-use bevy_ecs::system::Resource;
+use bevy_ecs::resource::Resource;
 use bevy_utils::HashMap;
 use core::{fmt::Display, hash::Hash, time::Duration};
 use thiserror::Error;

crates/bevy_asset/src/server/mod.rs

@@ -521,7 +521,8 @@ impl AssetServer {
     ///
     /// ```
     /// use bevy_asset::{Assets, Handle, LoadedUntypedAsset};
-    /// use bevy_ecs::system::{Res, Resource};
+    /// use bevy_ecs::system::Res;
+    /// use bevy_ecs::resource::Resource;
     ///
     /// #[derive(Resource)]
     /// struct LoadingUntypedHandle(Handle<LoadedUntypedAsset>);

crates/bevy_core_pipeline/src/bloom/downsampling_pipeline.rs

@@ -2,7 +2,8 @@ use super::{Bloom, BLOOM_SHADER_HANDLE, BLOOM_TEXTURE_FORMAT};
 use crate::fullscreen_vertex_shader::fullscreen_shader_vertex_state;
 use bevy_ecs::{
     prelude::{Component, Entity},
-    system::{Commands, Query, Res, ResMut, Resource},
+    resource::Resource,
+    system::{Commands, Query, Res, ResMut},
     world::{FromWorld, World},
 };
 use bevy_math::{Vec2, Vec4};

crates/bevy_core_pipeline/src/bloom/upsampling_pipeline.rs

@@ -5,7 +5,8 @@ use super::{
 use crate::fullscreen_vertex_shader::fullscreen_shader_vertex_state;
 use bevy_ecs::{
     prelude::{Component, Entity},
-    system::{Commands, Query, Res, ResMut, Resource},
+    resource::Resource,
+    system::{Commands, Query, Res, ResMut},
     world::{FromWorld, World},
 };
 use bevy_render::{

crates/bevy_core_pipeline/src/dof/mod.rs

@@ -22,8 +22,9 @@ use bevy_ecs::{
     entity::Entity,
     query::{QueryItem, With},
     reflect::ReflectComponent,
+    resource::Resource,
     schedule::IntoSystemConfigs as _,
-    system::{lifetimeless::Read, Commands, Query, Res, ResMut, Resource},
+    system::{lifetimeless::Read, Commands, Query, Res, ResMut},
     world::{FromWorld, World},
 };
 use bevy_image::BevyDefault as _;

crates/bevy_core_pipeline/src/motion_blur/pipeline.rs

@@ -2,7 +2,8 @@ use bevy_ecs::{
     component::Component,
     entity::Entity,
     query::With,
-    system::{Commands, Query, Res, ResMut, Resource},
+    resource::Resource,
+    system::{Commands, Query, Res, ResMut},
     world::FromWorld,
 };
 use bevy_image::BevyDefault as _;

crates/bevy_core_pipeline/src/post_process/mod.rs

@@ -10,8 +10,9 @@ use bevy_ecs::{
     entity::Entity,
     query::{QueryItem, With},
     reflect::ReflectComponent,
+    resource::Resource,
     schedule::IntoSystemConfigs as _,
-    system::{lifetimeless::Read, Commands, Query, Res, ResMut, Resource},
+    system::{lifetimeless::Read, Commands, Query, Res, ResMut},
     world::{FromWorld, World},
 };
 use bevy_image::{BevyDefault, Image};

crates/bevy_core_pipeline/src/skybox/mod.rs

@@ -3,8 +3,9 @@ use bevy_asset::{load_internal_asset, Handle};
 use bevy_ecs::{
     prelude::{Component, Entity},
     query::{QueryItem, With},
+    resource::Resource,
     schedule::IntoSystemConfigs,
-    system::{Commands, Query, Res, ResMut, Resource},
+    system::{Commands, Query, Res, ResMut},
 };
 use bevy_image::{BevyDefault, Image};
 use bevy_math::{Mat4, Quat};

crates/bevy_core_pipeline/src/skybox/prepass.rs

@@ -5,7 +5,8 @@ use bevy_ecs::{
     component::Component,
     entity::Entity,
     query::{Has, With},
-    system::{Commands, Query, Res, ResMut, Resource},
+    resource::Resource,
+    system::{Commands, Query, Res, ResMut},
     world::{FromWorld, World},
 };
 use bevy_render::{

crates/bevy_core_pipeline/src/smaa/mod.rs

@@ -45,8 +45,9 @@ use bevy_ecs::{
     entity::Entity,
     query::{QueryItem, With},
     reflect::ReflectComponent,
+    resource::Resource,
     schedule::IntoSystemConfigs as _,
-    system::{lifetimeless::Read, Commands, Query, Res, ResMut, Resource},
+    system::{lifetimeless::Read, Commands, Query, Res, ResMut},
     world::{FromWorld, World},
 };
 use bevy_image::{BevyDefault, Image};

crates/bevy_core_pipeline/src/taa/mod.rs

@@ -10,8 +10,9 @@ use bevy_diagnostic::FrameCount;
 use bevy_ecs::{
     prelude::{require, Component, Entity, ReflectComponent},
     query::{QueryItem, With},
+    resource::Resource,
     schedule::IntoSystemConfigs,
-    system::{Commands, Query, Res, ResMut, Resource},
+    system::{Commands, Query, Res, ResMut},
     world::{FromWorld, World},
 };
 use bevy_image::BevyDefault as _;

crates/bevy_dev_tools/src/fps_overlay.rs

@@ -9,8 +9,9 @@ use bevy_ecs::{
     component::Component,
     entity::Entity,
     query::With,
+    resource::Resource,
     schedule::{common_conditions::resource_changed, IntoSystemConfigs},
-    system::{Commands, Query, Res, Resource},
+    system::{Commands, Query, Res},
 };
 use bevy_render::view::Visibility;
 use bevy_text::{Font, TextColor, TextFont, TextSpan};

crates/bevy_diagnostic/src/diagnostic.rs

@@ -5,7 +5,8 @@ use core::{
 };
 
 use bevy_app::{App, SubApp};
-use bevy_ecs::system::{Deferred, Res, Resource, SystemBuffer, SystemParam};
+use bevy_ecs::resource::Resource;
+use bevy_ecs::system::{Deferred, Res, SystemBuffer, SystemParam};
 use bevy_platform_support::time::Instant;
 use bevy_utils::{HashMap, PassHash};
 use const_fnv1a_hash::fnv1a_hash_str_64;

crates/bevy_diagnostic/src/system_information_diagnostics_plugin.rs

@@ -1,6 +1,6 @@
 use crate::DiagnosticPath;
 use bevy_app::prelude::*;
-use bevy_ecs::system::Resource;
+use bevy_ecs::resource::Resource;
 
 /// Adds a System Information Diagnostic, specifically `cpu_usage` (in %) and `mem_usage` (in %)
 ///
@@ -64,7 +64,7 @@ pub mod internal {
     use std::{sync::Mutex, time::Instant};
 
     use bevy_app::{App, First, Startup, Update};
-    use bevy_ecs::system::Resource;
+    use bevy_ecs::resource::Resource;
     use bevy_tasks::{available_parallelism, block_on, poll_once, AsyncComputeTaskPool, Task};
     use sysinfo::{CpuRefreshKind, MemoryRefreshKind, RefreshKind, System};
     use tracing::info;

crates/bevy_ecs/macros/src/component.rs

@@ -46,7 +46,7 @@ pub fn derive_resource(input: TokenStream) -> TokenStream {
     let (impl_generics, type_generics, where_clause) = &ast.generics.split_for_impl();
 
     TokenStream::from(quote! {
-        impl #impl_generics #bevy_ecs_path::system::Resource for #struct_name #type_generics #where_clause {
+        impl #impl_generics #bevy_ecs_path::resource::Resource for #struct_name #type_generics #where_clause {
         }
     })
 }

crates/bevy_ecs/src/archetype.rs

@@ -766,7 +766,7 @@ struct ArchetypeComponents {
 ///
 /// [`Component`]: crate::component::Component
 /// [`World`]: crate::world::World
-/// [`Resource`]: crate::system::Resource
+/// [`Resource`]: crate::resource::Resource
 /// [many-to-many relationship]: https://en.wikipedia.org/wiki/Many-to-many_(data_model)
 #[derive(Debug, Copy, Clone, Eq, PartialEq, Hash)]
 pub struct ArchetypeComponentId(usize);

crates/bevy_ecs/src/change_detection.rs

@@ -3,7 +3,7 @@
 use crate::{
     component::{Tick, TickCells},
     ptr::PtrMut,
-    system::Resource,
+    resource::Resource,
 };
 use alloc::borrow::ToOwned;
 use bevy_ptr::{Ptr, UnsafeCellDeref};

crates/bevy_ecs/src/component.rs

@@ -7,8 +7,9 @@ use crate::{
     change_detection::MAX_CHANGE_AGE,
     entity::{ComponentCloneCtx, Entity},
     query::DebugCheckedUnwrap,
+    resource::Resource,
     storage::{SparseSetIndex, SparseSets, Storages, Table, TableRow},
-    system::{Local, Resource, SystemParam},
+    system::{Local, SystemParam},
     world::{DeferredWorld, FromWorld, World},
 };
 #[cfg(feature = "bevy_reflect")]

crates/bevy_ecs/src/event/collections.rs

@@ -2,7 +2,7 @@ use crate as bevy_ecs;
 use alloc::vec::Vec;
 use bevy_ecs::{
     event::{Event, EventCursor, EventId, EventInstance},
-    system::Resource,
+    resource::Resource,
 };
 #[cfg(feature = "track_location")]
 use core::panic::Location;

crates/bevy_ecs/src/event/registry.rs

@@ -4,7 +4,7 @@ use bevy_ecs::{
     change_detection::{DetectChangesMut, MutUntyped},
     component::{ComponentId, Tick},
     event::{Event, Events},
-    system::Resource,
+    resource::Resource,
     world::World,
 };
 

crates/bevy_ecs/src/lib.rs

@@ -52,6 +52,7 @@ pub mod query;
 pub mod reflect;
 pub mod relationship;
 pub mod removal_detection;
+pub mod resource;
 pub mod result;
 pub mod schedule;
 pub mod storage;
@@ -81,6 +82,7 @@ pub mod prelude {
         observer::{CloneEntityWithObserversExt, Observer, Trigger},
         query::{Added, AnyOf, Changed, Has, Or, QueryBuilder, QueryState, With, Without},
         removal_detection::RemovedComponents,
+        resource::Resource,
         result::{Error, Result},
         schedule::{
             apply_deferred, common_conditions::*, ApplyDeferred, Condition, IntoSystemConfigs,
@@ -89,7 +91,7 @@ pub mod prelude {
         system::{
             Command, Commands, Deferred, EntityCommand, EntityCommands, In, InMut, InRef,
             IntoSystem, Local, NonSend, NonSendMut, ParamSet, Populated, Query, ReadOnlySystem,
-            Res, ResMut, Resource, Single, System, SystemIn, SystemInput, SystemParamBuilder,
+            Res, ResMut, Single, System, SystemIn, SystemInput, SystemParamBuilder,
             SystemParamFunction, WithParamWarnPolicy,
         },
         world::{
@@ -134,7 +136,7 @@ mod tests {
         entity::Entity,
         prelude::Or,
         query::{Added, Changed, FilteredAccess, QueryFilter, With, Without},
-        system::Resource,
+        resource::Resource,
         world::{EntityMut, EntityRef, Mut, World},
     };
     use alloc::{
@@ -1223,7 +1225,7 @@ mod tests {
 
     #[test]
     fn resource() {
-        use crate::system::Resource;
+        use crate::resource::Resource;
 
         #[derive(Resource, PartialEq, Debug)]
         struct Num(i32);

crates/bevy_ecs/src/observer/entity_observer.rs

@@ -116,7 +116,8 @@ mod tests {
         entity::EntityCloneBuilder,
         event::Event,
         observer::{CloneEntityWithObserversExt, Trigger},
-        system::{ResMut, Resource},
+        resource::Resource,
+        system::ResMut,
         world::World,
     };
 

crates/bevy_ecs/src/reflect/entity_commands.rs

@@ -2,7 +2,8 @@ use crate::{
     entity::Entity,
     prelude::Mut,
     reflect::{AppTypeRegistry, ReflectBundle, ReflectComponent},
-    system::{EntityCommands, Resource},
+    resource::Resource,
+    system::EntityCommands,
     world::{EntityWorldMut, World},
 };
 use alloc::{borrow::Cow, boxed::Box};

crates/bevy_ecs/src/reflect/mod.rs

@@ -6,7 +6,7 @@ use core::{
 };
 
 use crate as bevy_ecs;
-use crate::{system::Resource, world::World};
+use crate::{resource::Resource, world::World};
 use bevy_reflect::{
     std_traits::ReflectDefault, PartialReflect, Reflect, ReflectFromReflect, TypePath,
     TypeRegistry, TypeRegistryArc,

crates/bevy_ecs/src/reflect/resource.rs

@@ -7,7 +7,7 @@
 use crate::{
     change_detection::Mut,
     component::ComponentId,
-    system::Resource,
+    resource::Resource,
     world::{unsafe_world_cell::UnsafeWorldCell, World},
 };
 use bevy_reflect::{FromReflect, FromType, PartialReflect, Reflect, TypePath, TypeRegistry};