Reflect auto registration

crates/bevy_app/src/app.rs

@@ -92,7 +92,7 @@ impl Default for App {
         app.sub_apps.main.update_schedule = Some(Main.intern());
 
         #[cfg(feature = "bevy_reflect")]
-        app.init_resource::<AppTypeRegistry>();
+        app.insert_resource(AppTypeRegistry::new_with_derived_types());
 
         #[cfg(feature = "reflect_functions")]
         app.init_resource::<AppFunctionRegistry>();

crates/bevy_ecs/src/reflect/mod.rs

@@ -49,6 +49,17 @@ impl DerefMut for AppTypeRegistry {
     }
 }
 
+impl AppTypeRegistry {
+    /// Creates [`AppTypeRegistry`] and calls [`register_derived_types`](TypeRegistry::register_derived_types) on it.
+    ///
+    /// See [`register_derived_types`](TypeRegistry::register_derived_types) for more details.
+    pub fn new_with_derived_types() -> Self {
+        let app_registry = AppTypeRegistry::default();
+        app_registry.write().register_derived_types();
+        app_registry
+    }
+}
+
 /// A [`Resource`] storing [`FunctionRegistry`] for
 /// function registrations relevant to a whole app.
 ///

crates/bevy_reflect/Cargo.toml

@@ -53,6 +53,12 @@ smol_str = { version = "0.2.0", features = ["serde"], optional = true }
 uuid = { version = "1.0", optional = true, features = ["v4", "serde"] }
 wgpu-types = { version = "23", features = ["serde"], optional = true }
 
+# deps for automatic type registration
+[target.'cfg(not(target_family = "wasm"))'.dependencies]
+inventory = "0.3"
+[target.'cfg(target_family = "wasm")'.dependencies]
+wasm-init = "0.2"
+
 [dev-dependencies]
 ron = "0.8.0"
 rmp-serde = "1.1"

crates/bevy_reflect/derive/src/container_attributes.rs

@@ -24,6 +24,7 @@ mod kw {
     syn::custom_keyword!(PartialEq);
     syn::custom_keyword!(Hash);
     syn::custom_keyword!(no_field_bounds);
+    syn::custom_keyword!(no_auto_register);
     syn::custom_keyword!(opaque);
 }
 
@@ -188,6 +189,7 @@ pub(crate) struct ContainerAttributes {
     type_path_attrs: TypePathAttrs,
     custom_where: Option<WhereClause>,
     no_field_bounds: bool,
+    no_auto_register: bool,
     custom_attributes: CustomAttributes,
     is_opaque: bool,
     idents: Vec<Ident>,
@@ -242,6 +244,8 @@ impl ContainerAttributes {
             self.parse_opaque(input)
         } else if lookahead.peek(kw::no_field_bounds) {
             self.parse_no_field_bounds(input)
+        } else if lookahead.peek(kw::no_auto_register) {
+            self.parse_no_auto_register(input)
         } else if lookahead.peek(kw::Debug) {
             self.parse_debug(input)
         } else if lookahead.peek(kw::PartialEq) {
@@ -360,6 +364,16 @@ impl ContainerAttributes {
         Ok(())
     }
 
+    /// Parse `no_auto_register` attribute.
+    ///
+    /// Examples:
+    /// - `#[reflect(no_auto_register)]`
+    fn parse_no_auto_register(&mut self, input: ParseStream) -> syn::Result<()> {
+        input.parse::<kw::no_auto_register>()?;
+        self.no_auto_register = true;
+        Ok(())
+    }
+
     /// Parse `where` attribute.
     ///
     /// Examples:
@@ -543,6 +557,11 @@ impl ContainerAttributes {
         self.no_field_bounds
     }
 
+    /// Returns true if the `no_auto_register` attribute was found on this type.
+    pub fn no_auto_register(&self) -> bool {
+        self.no_auto_register
+    }
+
     /// Returns true if the `opaque` attribute was found on this type.
     pub fn is_opaque(&self) -> bool {
         self.is_opaque

crates/bevy_reflect/derive/src/impls/common.rs

@@ -1,6 +1,6 @@
 use bevy_macro_utils::fq_std::{FQAny, FQBox, FQOption, FQResult};
 
-use quote::quote;
+use quote::{quote, ToTokens};
 
 use crate::{derive_data::ReflectMeta, where_clause_options::WhereClauseOptions};
 
@@ -156,3 +156,25 @@ pub fn common_partial_reflect_methods(
         #debug_fn
     }
 }
+
+pub fn reflect_auto_registration(meta: &ReflectMeta) -> Option<proc_macro2::TokenStream> {
+    if meta.attrs().no_auto_register() {
+        return None;
+    }
+
+    let bevy_reflect_path = meta.bevy_reflect_path();
+    let type_path = meta.type_path();
+    let generics = meta.type_path().generics();
+
+    if !generics.into_token_stream().is_empty() {
+        return None;
+    };
+
+    Some(quote! {
+        #bevy_reflect_path::__macro_exports::auto_register_function!{
+            #bevy_reflect_path::__macro_exports::AutomaticReflectRegistrations::add(
+                <#type_path as #bevy_reflect_path::__macro_exports::RegisterForReflection>::__register
+            )
+        }
+    })
+}

crates/bevy_reflect/derive/src/impls/enums.rs

@@ -1,7 +1,10 @@
 use crate::{
     derive_data::{EnumVariantFields, ReflectEnum, StructField},
     enum_utility::{EnumVariantOutputData, TryApplyVariantBuilder, VariantBuilder},
-    impls::{common_partial_reflect_methods, impl_full_reflect, impl_type_path, impl_typed},
+    impls::{
+        common_partial_reflect_methods, impl_full_reflect, impl_type_path, impl_typed,
+        reflect_auto_registration,
+    },
 };
 use bevy_macro_utils::fq_std::{FQBox, FQOption, FQResult};
 use proc_macro2::{Ident, Span};
@@ -82,6 +85,8 @@ pub(crate) fn impl_enum(reflect_enum: &ReflectEnum) -> proc_macro2::TokenStream
     let (impl_generics, ty_generics, where_clause) =
         reflect_enum.meta().type_path().generics().split_for_impl();
 
+    let auto_register = reflect_auto_registration(reflect_enum.meta());
+
     let where_reflect_clause = where_clause_options.extend_where_clause(where_clause);
 
     quote! {
@@ -95,6 +100,8 @@ pub(crate) fn impl_enum(reflect_enum: &ReflectEnum) -> proc_macro2::TokenStream
 
         #function_impls
 
+        #auto_register
+
         impl #impl_generics #bevy_reflect_path::Enum for #enum_path #ty_generics #where_reflect_clause {
             fn field(&self, #ref_name: &str) -> #FQOption<&dyn #bevy_reflect_path::PartialReflect> {
                  match #match_this {

crates/bevy_reflect/derive/src/impls/mod.rs

@@ -9,7 +9,9 @@ mod tuple_structs;
 mod typed;
 
 pub(crate) use assertions::impl_assertions;
-pub(crate) use common::{common_partial_reflect_methods, impl_full_reflect};
+pub(crate) use common::{
+    common_partial_reflect_methods, impl_full_reflect, reflect_auto_registration,
+};
 pub(crate) use enums::impl_enum;
 #[cfg(feature = "functions")]
 pub(crate) use func::impl_function_traits;

crates/bevy_reflect/derive/src/impls/structs.rs

@@ -1,5 +1,8 @@
 use crate::{
-    impls::{common_partial_reflect_methods, impl_full_reflect, impl_type_path, impl_typed},
+    impls::{
+        common_partial_reflect_methods, impl_full_reflect, impl_type_path, impl_typed,
+        reflect_auto_registration,
+    },
     struct_utility::FieldAccessors,
     ReflectStruct,
 };
@@ -62,6 +65,8 @@ pub(crate) fn impl_struct(reflect_struct: &ReflectStruct) -> proc_macro2::TokenS
         .generics()
         .split_for_impl();
 
+    let auto_register = reflect_auto_registration(reflect_struct.meta());
+
     let where_reflect_clause = where_clause_options.extend_where_clause(where_clause);
 
     quote! {
@@ -75,6 +80,8 @@ pub(crate) fn impl_struct(reflect_struct: &ReflectStruct) -> proc_macro2::TokenS
 
         #function_impls
 
+        #auto_register
+
         impl #impl_generics #bevy_reflect_path::Struct for #struct_path #ty_generics #where_reflect_clause {
             fn field(&self, name: &str) -> #FQOption<&dyn #bevy_reflect_path::PartialReflect> {
                 match name {

crates/bevy_reflect/derive/src/impls/tuple_structs.rs

@@ -1,5 +1,8 @@
 use crate::{
-    impls::{common_partial_reflect_methods, impl_full_reflect, impl_type_path, impl_typed},
+    impls::{
+        common_partial_reflect_methods, impl_full_reflect, impl_type_path, impl_typed,
+        reflect_auto_registration,
+    },
     struct_utility::FieldAccessors,
     ReflectStruct,
 };
@@ -50,6 +53,8 @@ pub(crate) fn impl_tuple_struct(reflect_struct: &ReflectStruct) -> proc_macro2::
         .generics()
         .split_for_impl();
 
+    let auto_register = reflect_auto_registration(reflect_struct.meta());
+
     let where_reflect_clause = where_clause_options.extend_where_clause(where_clause);
 
     quote! {
@@ -63,6 +68,8 @@ pub(crate) fn impl_tuple_struct(reflect_struct: &ReflectStruct) -> proc_macro2::
 
         #function_impls
 
+        #auto_register
+
         impl #impl_generics #bevy_reflect_path::TupleStruct for #struct_path #ty_generics #where_reflect_clause {
             fn field(&self, index: usize) -> #FQOption<&dyn #bevy_reflect_path::PartialReflect> {
                 match index {

crates/bevy_reflect/derive/src/lib.rs

@@ -315,6 +315,12 @@ fn match_reflect_impls(ast: DeriveInput, source: ReflectImplSource) -> TokenStre
 /// #[reflect(@Required, @EditorTooltip::new("An ID is required!"))]
 /// struct Id(u8);
 /// ```
+/// ## `#[reflect(no_auto_register)]`
+///
+/// This attribute will opt-out of the automatic reflect type registration.
+///
+/// All non-generic types annotated with `#[derive(Reflect)]` are usually automatically registered on app startup.
+/// If this behavior is not desired, this attribute may be used to disable it for the annotated type.
 ///
 /// # Field Attributes
 ///

crates/bevy_reflect/src/lib.rs

@@ -460,12 +460,11 @@
 //! typically require manual monomorphization (i.e. manually specifying the types the generic method can
 //! take).
 //!
-//! ## Manual Registration
+//! ## Manual Registration of Generic Types
 //!
-//! Since Rust doesn't provide built-in support for running initialization code before `main`,
-//! there is no way for `bevy_reflect` to automatically register types into the [type registry].
-//! This means types must manually be registered, including their desired monomorphized
-//! representations if generic.
+//! `bevy_reflect` automatically collects all types that derive [`Reflect`] on startup,
+//! and [`TypeRegistry::register_derived_types`] can be used to register these types at any point in the program.
+//! However, this does not apply to types with generics: their desired monomorphized representations must be registered manually.
 //!
 //! # Features
 //!
@@ -687,6 +686,77 @@ pub mod __macro_exports {
     impl RegisterForReflection for DynamicArray {}
 
     impl RegisterForReflection for DynamicTuple {}
+
+    /// Stores registration functions of all reflect types that can be automatically registered.
+    ///
+    /// Intended to be used as follows:
+    /// ```rs
+    /// // Adding a type
+    /// auto_register_function!{
+    ///     AutomaticReflectRegistrations::add(<type_registration_function>)
+    /// }
+    ///
+    /// // Registering collected types
+    /// let mut registry = TypeRegistry::default();
+    /// AutomaticReflectRegistrations::register(&mut registry);
+    /// ```
+    pub struct AutomaticReflectRegistrations;
+
+    #[cfg(not(target_family = "wasm"))]
+    mod __automatic_type_registration_impl {
+        use super::*;
+
+        pub use inventory::submit as auto_register_function;
+
+        pub struct AutomaticReflectRegistrationsImpl(fn(&mut TypeRegistry));
+
+        impl AutomaticReflectRegistrations {
+            // Must be const to allow usage in static context
+            pub const fn add(func: fn(&mut TypeRegistry)) -> AutomaticReflectRegistrationsImpl {
+                AutomaticReflectRegistrationsImpl(func)
+            }
+            pub fn register(registry: &mut TypeRegistry) {
+                for registration_fn in inventory::iter::<AutomaticReflectRegistrationsImpl> {
+                    registration_fn.0(registry);
+                }
+            }
+        }
+
+        inventory::collect!(AutomaticReflectRegistrationsImpl);
+    }
+
+    #[cfg(target_family = "wasm")]
+    mod __automatic_type_registration_impl {
+        use super::*;
+        pub use wasm_init::wasm_init as auto_register_function;
+
+        static AUTOMATIC_REFLECT_REGISTRATIONS: std::sync::RwLock<Vec<fn(&mut TypeRegistry)>> =
+            std::sync::RwLock::new(Vec::new());
+
+        impl AutomaticReflectRegistrations {
+            pub fn add(func: fn(&mut TypeRegistry)) {
+                AUTOMATIC_REFLECT_REGISTRATIONS
+                    .write()
+                    .expect("Failed to get write lock for automatic reflect type registration")
+                    .push(func);
+            }
+            pub fn register(registry: &mut TypeRegistry) {
+                // wasm_init must be called at least once to run all init code.
+                // Calling it multiple times is ok and doesn't do anything.
+                wasm_init::wasm_init();
+
+                for registration_fn in AUTOMATIC_REFLECT_REGISTRATIONS
+                    .read()
+                    .expect("Failed to get read lock for automatic reflect type registration")
+                    .iter()
+                {
+                    registration_fn(registry);
+                }
+            }
+        }
+    }
+
+    pub use __automatic_type_registration_impl::*;
 }
 
 #[cfg(test)]
@@ -2975,6 +3045,20 @@ bevy_reflect::tests::Test {
         );
     }
 
+    #[test]
+    fn should_ignore_auto_reflect_registration() {
+        #[derive(Reflect)]
+        #[reflect(no_auto_register)]
+        struct NoAutomaticStruct {
+            a: usize,
+        }
+
+        let mut registry = TypeRegistry::default();
+        registry.register_derived_types();
+
+        assert!(!registry.contains(TypeId::of::<NoAutomaticStruct>()));
+    }
+
     #[cfg(feature = "glam")]
     mod glam {
         use super::*;

crates/bevy_reflect/src/type_registry.rs

@@ -117,6 +117,43 @@ impl TypeRegistry {
         registry
     }
 
+    /// Register all non-generic types annotated with `#[derive(Reflect)]`.
+    ///
+    /// Calling this method is equivalent to calling [`register`](Self::register) on all types without generic parameters
+    /// that derived [`Reflect`] trait.
+    ///
+    /// This method is supported on Linux, macOS, iOS, Android and Windows via the `inventory` crate,
+    /// and on wasm via the `wasm-init` crate. It does nothing on platforms not supported by either of those crates.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// # use std::any::TypeId;
+    /// # use bevy_reflect::{Reflect, TypeRegistry, std_traits::ReflectDefault};
+    /// #[derive(Reflect, Default)]
+    /// #[reflect(Default)]
+    /// struct Foo {
+    ///   name: Option<String>,
+    ///   value: i32
+    /// }
+    ///
+    /// let mut type_registry = TypeRegistry::empty();
+    /// type_registry.register_derived_types();
+    ///
+    /// // The main type
+    /// assert!(type_registry.contains(TypeId::of::<Foo>()));
+    ///
+    /// // Its type dependencies
+    /// assert!(type_registry.contains(TypeId::of::<Option<String>>()));
+    /// assert!(type_registry.contains(TypeId::of::<i32>()));
+    ///
+    /// // Its type data
+    /// assert!(type_registry.get_type_data::<ReflectDefault>(TypeId::of::<Foo>()).is_some());
+    /// ```
+    pub fn register_derived_types(&mut self) {
+        crate::__macro_exports::AutomaticReflectRegistrations::register(self);
+    }
+
     /// Attempts to register the type `T` if it has not yet been registered already.
     ///
     /// This will also recursively register any type dependencies as specified by [`GetTypeRegistration::register_type_dependencies`].