Make Resource trait opt-in, requiring #[derive(Resource)] V2 (#5577)

*This PR description is an edited copy of #5007, written by @alice-i-cecile.*
# Objective
Follow-up to #2254. The `Resource` trait currently has a blanket implementation for all types that meet its bounds.

While ergonomic, this results in several drawbacks:

* it is possible to make confusing, silent mistakes such as inserting a function pointer (Foo) rather than a value (Foo::Bar) as a resource
* it is challenging to discover if a type is intended to be used as a resource
* we cannot later add customization options (see the [RFC](https://github.com/bevyengine/rfcs/blob/main/rfcs/27-derive-component.md) for the equivalent choice for Component).
* dependencies can use the same Rust type as a resource in invisibly conflicting ways
* raw Rust types used as resources cannot preserve privacy appropriately, as anyone able to access that type can read and write to internal values
* we cannot capture a definitive list of possible resources to display to users in an editor
## Notes to reviewers
 * Review this commit-by-commit; there's effectively no back-tracking and there's a lot of churn in some of these commits.
   *ira: My commits are not as well organized :')*
 * I've relaxed the bound on Local to Send + Sync + 'static: I don't think these concerns apply there, so this can keep things simple. Storing e.g. a u32 in a Local is fine, because there's a variable name attached explaining what it does.
 * I think this is a bad place for the Resource trait to live, but I've left it in place to make reviewing easier. IMO that's best tackled with #4981.

## Changelog
`Resource` is no longer automatically implemented for all matching types. Instead, use the new `#[derive(Resource)]` macro.

## Migration Guide
Add `#[derive(Resource)]` to all types you are using as a resource.

If you are using a third party type as a resource, wrap it in a tuple struct to bypass orphan rules. Consider deriving `Deref` and `DerefMut` to improve ergonomics.

`ClearColor` no longer implements `Component`. Using `ClearColor` as a component in 0.8 did nothing.
Use the `ClearColorConfig` in the `Camera3d` and `Camera2d` components instead.


Co-authored-by: Alice <alice.i.cecile@gmail.com>
Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>
Co-authored-by: devil-ira <justthecooldude@gmail.com>
Co-authored-by: Carter Anderson <mcanders1@gmail.com>

Author: 3 people

benches/benches/bevy_ecs/scheduling/run_criteria.rs

@@ -1,6 +1,6 @@
 use bevy_ecs::{
     component::Component,
-    prelude::{ParallelSystemDescriptorCoercion, Res, RunCriteriaDescriptorCoercion},
+    prelude::{ParallelSystemDescriptorCoercion, Res, Resource, RunCriteriaDescriptorCoercion},
     schedule::{ShouldRun, Stage, SystemStage},
     system::Query,
     world::World,
@@ -136,7 +136,7 @@ pub fn run_criteria_no_with_labels(criterion: &mut Criterion) {
     group.finish();
 }
 
-#[derive(Component)]
+#[derive(Component, Resource)]
 struct TestBool(pub bool);
 
 pub fn run_criteria_yes_with_query(criterion: &mut Criterion) {

crates/bevy_app/src/app.rs

@@ -1,5 +1,6 @@
 use crate::{CoreStage, Plugin, PluginGroup, PluginGroupBuilder, StartupSchedule, StartupStage};
 pub use bevy_derive::AppLabel;
+use bevy_derive::{Deref, DerefMut};
 use bevy_ecs::{
     event::{Event, Events},
     prelude::{FromWorld, IntoExclusiveSystem},
@@ -22,6 +23,11 @@ bevy_utils::define_label!(
     AppLabelId,
 );
 
+/// The [`Resource`] that stores the [`App`]'s [`TypeRegistry`](bevy_reflect::TypeRegistry).
+#[cfg(feature = "bevy_reflect")]
+#[derive(Resource, Clone, Deref, DerefMut, Default)]
+pub struct AppTypeRegistry(pub bevy_reflect::TypeRegistryArc);
+
 #[allow(clippy::needless_doctest_main)]
 /// A container of app logic and data.
 ///
@@ -74,7 +80,7 @@ impl Default for App {
     fn default() -> Self {
         let mut app = App::empty();
         #[cfg(feature = "bevy_reflect")]
-        app.init_resource::<bevy_reflect::TypeRegistryArc>();
+        app.init_resource::<AppTypeRegistry>();
 
         app.add_default_stages()
             .add_event::<AppExit>()
@@ -647,7 +653,9 @@ impl App {
     ///
     /// ```
     /// # use bevy_app::prelude::*;
+    /// # use bevy_ecs::prelude::*;
     /// #
+    /// #[derive(Resource)]
     /// struct MyCounter {
     ///     counter: usize,
     /// }
@@ -660,15 +668,16 @@ impl App {
         self
     }
 
-    /// Inserts a non-send [`Resource`] to the app.
+    /// Inserts a non-send resource to the app.
     ///
     /// You usually want to use [`insert_resource`](Self::insert_resource),
-    /// but there are some special cases when a [`Resource`] cannot be sent across threads.
+    /// but there are some special cases when a resource cannot be sent across threads.
     ///
     /// # Examples
     ///
     /// ```
     /// # use bevy_app::prelude::*;
+    /// # use bevy_ecs::prelude::*;
     /// #
     /// struct MyCounter {
     ///     counter: usize,
@@ -694,7 +703,9 @@ impl App {
     ///
     /// ```
     /// # use bevy_app::prelude::*;
+    /// # use bevy_ecs::prelude::*;
     /// #
+    /// #[derive(Resource)]
     /// struct MyCounter {
     ///     counter: usize,
     /// }
@@ -873,7 +884,7 @@ impl App {
     #[cfg(feature = "bevy_reflect")]
     pub fn register_type<T: bevy_reflect::GetTypeRegistration>(&mut self) -> &mut Self {
         {
-            let registry = self.world.resource_mut::<bevy_reflect::TypeRegistryArc>();
+            let registry = self.world.resource_mut::<AppTypeRegistry>();
             registry.write().register::<T>();
         }
         self
@@ -906,7 +917,7 @@ impl App {
         &mut self,
     ) -> &mut Self {
         {
-            let registry = self.world.resource_mut::<bevy_reflect::TypeRegistryArc>();
+            let registry = self.world.resource_mut::<AppTypeRegistry>();
             registry.write().register_type_data::<T, D>();
         }
         self

crates/bevy_app/src/ci_testing.rs

@@ -1,14 +1,15 @@
 use crate::{app::AppExit, App};
 use serde::Deserialize;
 
+use bevy_ecs::prelude::Resource;
 use bevy_utils::tracing::info;
 
 /// A configuration struct for automated CI testing.
 ///
 /// It gets used when the `bevy_ci_testing` feature is enabled to automatically
 /// exit a Bevy app when run through the CI. This is needed because otherwise
 /// Bevy apps would be stuck in the game loop and wouldn't allow the CI to progress.
-#[derive(Deserialize)]
+#[derive(Deserialize, Resource)]
 pub struct CiTestingConfig {
     /// The number of frames after which Bevy should exit.
     pub exit_after: Option<u32>,

crates/bevy_app/src/lib.rs

@@ -18,6 +18,9 @@ pub use schedule_runner::*;
 
 #[allow(missing_docs)]
 pub mod prelude {
+    #[cfg(feature = "bevy_reflect")]
+    #[doc(hidden)]
+    pub use crate::AppTypeRegistry;
     #[doc(hidden)]
     pub use crate::{
         app::App, CoreStage, DynamicPlugin, Plugin, PluginGroup, StartupSchedule, StartupStage,

crates/bevy_app/src/schedule_runner.rs

@@ -3,6 +3,7 @@ use crate::{
     plugin::Plugin,
 };
 use bevy_ecs::event::{Events, ManualEventReader};
+use bevy_ecs::prelude::Resource;
 use bevy_utils::{Duration, Instant};
 
 #[cfg(target_arch = "wasm32")]
@@ -34,7 +35,7 @@ impl Default for RunMode {
 /// The configuration information for the [`ScheduleRunnerPlugin`].
 ///
 /// It gets added as a [`Resource`](bevy_ecs::system::Resource) inside of the [`ScheduleRunnerPlugin`].
-#[derive(Copy, Clone, Default)]
+#[derive(Copy, Clone, Default, Resource)]
 pub struct ScheduleRunnerSettings {
     /// Determines whether the [`Schedule`](bevy_ecs::schedule::Schedule) is run once or repeatedly.
     pub run_mode: RunMode,

crates/bevy_asset/src/asset_server.rs

@@ -5,7 +5,7 @@ use crate::{
     RefChange, RefChangeChannel, SourceInfo, SourceMeta,
 };
 use anyhow::Result;
-use bevy_ecs::system::{Res, ResMut};
+use bevy_ecs::system::{Res, ResMut, Resource};
 use bevy_log::warn;
 use bevy_tasks::IoTaskPool;
 use bevy_utils::{Entry, HashMap, Uuid};
@@ -102,7 +102,7 @@ pub struct AssetServerInternal {
 /// See the [`asset_loading`] example for more information.
 ///
 /// [`asset_loading`]: https://github.com/bevyengine/bevy/tree/latest/examples/asset/asset_loading.rs
-#[derive(Clone)]
+#[derive(Clone, Resource)]
 pub struct AssetServer {
     pub(crate) server: Arc<AssetServerInternal>,
 }

crates/bevy_asset/src/assets.rs

@@ -5,7 +5,7 @@ use crate::{
 use bevy_app::App;
 use bevy_ecs::{
     event::{EventWriter, Events},
-    system::ResMut,
+    system::{ResMut, Resource},
     world::FromWorld,
 };
 use bevy_utils::HashMap;
@@ -66,7 +66,7 @@ impl<T: Asset> Debug for AssetEvent<T> {
 /// Remember, if there are no Strong handles for an asset (i.e. they have all been dropped), the
 /// asset will unload. Make sure you always have a Strong handle when you want to keep an asset
 /// loaded!
-#[derive(Debug)]
+#[derive(Debug, Resource)]
 pub struct Assets<T: Asset> {
     assets: HashMap<HandleId, T>,
     events: Events<AssetEvent<T>>,

crates/bevy_asset/src/debug_asset_server.rs

@@ -6,7 +6,7 @@ use bevy_app::{App, Plugin};
 use bevy_ecs::{
     event::Events,
     schedule::SystemLabel,
-    system::{NonSendMut, Res, ResMut, SystemState},
+    system::{NonSendMut, Res, ResMut, Resource, SystemState},
 };
 use bevy_tasks::{IoTaskPool, TaskPoolBuilder};
 use bevy_utils::HashMap;
@@ -52,6 +52,7 @@ pub struct DebugAssetServerPlugin;
 
 /// A collection that maps internal assets in a [`DebugAssetApp`]'s asset server to their mirrors in
 /// the main [`App`].
+#[derive(Resource)]
 pub struct HandleMap<T: Asset> {
     /// The collection of asset handles.
     pub handles: HashMap<Handle<T>, Handle<T>>,

crates/bevy_asset/src/lib.rs

@@ -43,7 +43,10 @@ pub use loader::*;
 pub use path::*;
 
 use bevy_app::{prelude::Plugin, App};
-use bevy_ecs::schedule::{StageLabel, SystemStage};
+use bevy_ecs::{
+    schedule::{StageLabel, SystemStage},
+    system::Resource,
+};
 
 /// The names of asset stages in an [`App`] schedule.
 #[derive(Debug, Hash, PartialEq, Eq, Clone, StageLabel)]
@@ -62,6 +65,7 @@ pub enum AssetStage {
 pub struct AssetPlugin;
 
 /// [`AssetServer`] settings.
+#[derive(Resource)]
 pub struct AssetServerSettings {
     /// The base folder where assets are loaded from, relative to the executable.
     pub asset_folder: String,

crates/bevy_audio/src/audio.rs

@@ -1,9 +1,10 @@
 use crate::{AudioSink, AudioSource, Decodable};
 use bevy_asset::{Asset, Handle, HandleId};
+use bevy_ecs::system::Resource;
 use parking_lot::RwLock;
 use std::{collections::VecDeque, fmt};
 
-/// Use this resource to play audio
+/// Use this [`Resource`] to play audio.
 ///
 /// ```
 /// # use bevy_ecs::system::Res;
@@ -13,6 +14,7 @@ use std::{collections::VecDeque, fmt};
 ///     audio.play(asset_server.load("my_sound.ogg"));
 /// }
 /// ```
+#[derive(Resource)]
 pub struct Audio<Source = AudioSource>
 where
     Source: Asset + Decodable,

crates/bevy_core/src/task_pool_options.rs

@@ -1,3 +1,4 @@
+use bevy_ecs::prelude::Resource;
 use bevy_tasks::{AsyncComputeTaskPool, ComputeTaskPool, IoTaskPool, TaskPoolBuilder};
 use bevy_utils::tracing::trace;
 
@@ -33,7 +34,7 @@ impl TaskPoolThreadAssignmentPolicy {
 /// Helper for configuring and creating the default task pools. For end-users who want full control,
 /// insert the default task pools into the resource map manually. If the pools are already inserted,
 /// this helper will do nothing.
-#[derive(Clone)]
+#[derive(Clone, Resource)]
 pub struct DefaultTaskPoolOptions {
     /// If the number of physical cores is less than min_total_threads, force using
     /// min_total_threads

crates/bevy_core_pipeline/src/clear_color.rs

@@ -13,11 +13,11 @@ pub enum ClearColorConfig {
     None,
 }
 
-/// When used as a resource, sets the color that is used to clear the screen between frames.
+/// A [`Resource`] that stores the color that is used to clear the screen between frames.
 ///
-/// This color appears as the "background" color for simple apps, when
-/// there are portions of the screen with nothing rendered.
-#[derive(Component, Clone, Debug, Deref, DerefMut, ExtractResource, Reflect)]
+/// This color appears as the "background" color for simple apps,
+/// when there are portions of the screen with nothing rendered.
+#[derive(Resource, Clone, Debug, Deref, DerefMut, ExtractResource, Reflect)]
 #[reflect(Resource)]
 pub struct ClearColor(pub Color);
 

crates/bevy_diagnostic/src/diagnostic.rs

@@ -1,3 +1,4 @@
+use bevy_ecs::system::Resource;
 use bevy_log::warn;
 use bevy_utils::{Duration, Instant, StableHashMap, Uuid};
 use std::{borrow::Cow, collections::VecDeque};
@@ -154,7 +155,7 @@ impl Diagnostic {
 }
 
 /// A collection of [Diagnostic]s
-#[derive(Debug, Default)]
+#[derive(Debug, Default, Resource)]
 pub struct Diagnostics {
     // This uses a [`StableHashMap`] to ensure that the iteration order is deterministic between
     // runs when all diagnostics are inserted in the same order.

crates/bevy_diagnostic/src/frame_time_diagnostics_plugin.rs

@@ -1,12 +1,13 @@
 use crate::{Diagnostic, DiagnosticId, Diagnostics};
 use bevy_app::prelude::*;
-use bevy_ecs::system::{Res, ResMut};
+use bevy_ecs::system::{Res, ResMut, Resource};
 use bevy_time::Time;
 
 /// Adds "frame time" diagnostic to an App, specifically "frame time", "fps" and "frame count"
 #[derive(Default)]
 pub struct FrameTimeDiagnosticsPlugin;
 
+#[derive(Resource)]
 pub struct FrameTimeDiagnosticsState {
     frame_count: u64,
 }

crates/bevy_diagnostic/src/log_diagnostics_plugin.rs

@@ -1,6 +1,6 @@
 use super::{Diagnostic, DiagnosticId, Diagnostics};
 use bevy_app::prelude::*;
-use bevy_ecs::system::{Res, ResMut};
+use bevy_ecs::system::{Res, ResMut, Resource};
 use bevy_log::{debug, info};
 use bevy_time::{Time, Timer};
 use bevy_utils::Duration;
@@ -13,6 +13,7 @@ pub struct LogDiagnosticsPlugin {
 }
 
 /// State used by the [`LogDiagnosticsPlugin`]
+#[derive(Resource)]
 struct LogDiagnosticsState {
     timer: Timer,
     filter: Option<Vec<DiagnosticId>>,

crates/bevy_ecs/README.md

@@ -91,7 +91,7 @@ Apps often require unique resources, such as asset collections, renderers, audio
 ```rust
 use bevy_ecs::prelude::*;
 
-#[derive(Default)]
+#[derive(Resource, Default)]
 struct Time {
     seconds: f32,
 }
@@ -213,6 +213,7 @@ Resources also expose change state:
 ```rust
 use bevy_ecs::prelude::*;
 
+#[derive(Resource)]
 struct Time(f32);
 
 // Prints "time changed!" if the Time resource has changed since the last run of the System

crates/bevy_ecs/examples/change_detection.rs

@@ -40,7 +40,7 @@ fn main() {
 }
 
 // This struct will be used as a Resource keeping track of the total amount of spawned entities
-#[derive(Debug)]
+#[derive(Debug, Resource)]
 struct EntityCounter {
     pub value: i32,
 }

crates/bevy_ecs/examples/resources.rs

@@ -27,7 +27,7 @@ fn main() {
 }
 
 // Counter resource to be increased and read by systems
-#[derive(Debug)]
+#[derive(Debug, Resource)]
 struct Counter {
     pub value: i32,
 }

crates/bevy_ecs/macros/src/component.rs

@@ -4,6 +4,24 @@ use proc_macro2::{Span, TokenStream as TokenStream2};
 use quote::{quote, ToTokens};
 use syn::{parse_macro_input, parse_quote, DeriveInput, Error, Ident, Path, Result};
 
+pub fn derive_resource(input: TokenStream) -> TokenStream {
+    let mut ast = parse_macro_input!(input as DeriveInput);
+    let bevy_ecs_path: Path = crate::bevy_ecs_path();
+
+    ast.generics
+        .make_where_clause()
+        .predicates
+        .push(parse_quote! { Self: Send + Sync + 'static });
+
+    let struct_name = &ast.ident;
+    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 {
+        }
+    })
+}
+
 pub fn derive_component(input: TokenStream) -> TokenStream {
     let mut ast = parse_macro_input!(input as DeriveInput);
     let bevy_ecs_path: Path = crate::bevy_ecs_path();

crates/bevy_ecs/macros/src/lib.rs

@@ -496,6 +496,11 @@ pub(crate) fn bevy_ecs_path() -> syn::Path {
     BevyManifest::default().get_path("bevy_ecs")
 }
 
+#[proc_macro_derive(Resource)]
+pub fn derive_resource(input: TokenStream) -> TokenStream {
+    component::derive_resource(input)
+}
+
 #[proc_macro_derive(Component, attributes(component))]
 pub fn derive_component(input: TokenStream) -> TokenStream {
     component::derive_component(input)