Bevy derives handling generics in impl definitions. (#2044)

Fixes #2037 (and then some)

Problem:
- `TypeUuid`, `RenderResource`, and `Bytes` derive macros did not properly handle generic structs. 

Solution:
- Rework the derive macro implementations to handle the generics.

crates/bevy_derive/src/bytes.rs

@@ -21,13 +21,11 @@ pub fn derive_bytes(input: TokenStream) -> TokenStream {
         .map(|field| field.ident.as_ref().unwrap())
         .collect::<Vec<_>>();
 
-    let generics = ast.generics;
-    let (impl_generics, ty_generics, _where_clause) = generics.split_for_impl();
-
     let struct_name = &ast.ident;
+    let (impl_generics, ty_generics, where_clause) = ast.generics.split_for_impl();
 
     TokenStream::from(quote! {
-        impl #impl_generics #bevy_core_path::Bytes for #struct_name#ty_generics {
+        impl #impl_generics #bevy_core_path::Bytes for #struct_name #ty_generics #where_clause {
             fn write_bytes(&self, buffer: &mut [u8]) {
                 let mut offset: usize = 0;
                 #(let byte_len = self.#fields.byte_len();

crates/bevy_derive/src/render_resource.rs

@@ -11,9 +11,10 @@ pub fn derive_render_resource(input: TokenStream) -> TokenStream {
     let bevy_asset_path: Path = get_path(&modules.bevy_asset);
     let bevy_core_path: Path = get_path(&modules.bevy_core);
     let struct_name = &ast.ident;
+    let (impl_generics, type_generics, where_clause) = &ast.generics.split_for_impl();
 
     TokenStream::from(quote! {
-        impl #bevy_render_path::renderer::RenderResource for #struct_name {
+        impl #impl_generics #bevy_render_path::renderer::RenderResource for #struct_name #type_generics #where_clause {
             fn resource_type(&self) -> Option<#bevy_render_path::renderer::RenderResourceType> {
                 Some(#bevy_render_path::renderer::RenderResourceType::Buffer)
             }

crates/bevy_derive/src/render_resources.rs

@@ -42,11 +42,12 @@ pub fn derive_render_resources(input: TokenStream) -> TokenStream {
             attributes
         });
     let struct_name = &ast.ident;
+    let (impl_generics, type_generics, where_clause) = &ast.generics.split_for_impl();
     let struct_name_string = struct_name.to_string();
 
     if attributes.from_self {
         TokenStream::from(quote! {
-            impl #bevy_render_path::renderer::RenderResources for #struct_name {
+            impl #impl_generics #bevy_render_path::renderer::RenderResources for #struct_name #type_generics #where_clause {
                 fn render_resources_len(&self) -> usize {
                     1
                 }
@@ -154,7 +155,7 @@ pub fn derive_render_resources(input: TokenStream) -> TokenStream {
                 #(#render_resource_hints,)*
             ];
 
-            impl #bevy_render_path::renderer::RenderResources for #struct_name {
+            impl #impl_generics #bevy_render_path::renderer::RenderResources for #struct_name #type_generics #where_clause {
                 fn render_resources_len(&self) -> usize {
                     #render_resource_count
                 }

crates/bevy_reflect/bevy_reflect_derive/src/type_uuid.rs

@@ -15,6 +15,7 @@ pub fn type_uuid_derive(input: proc_macro::TokenStream) -> proc_macro::TokenStre
 
     // Build the trait implementation
     let name = &ast.ident;
+    let (impl_generics, type_generics, where_clause) = &ast.generics.split_for_impl();
 
     let mut uuid = None;
     for attribute in ast.attrs.iter().filter_map(|attr| attr.parse_meta().ok()) {
@@ -53,7 +54,7 @@ pub fn type_uuid_derive(input: proc_macro::TokenStream) -> proc_macro::TokenStre
         .map(|byte_str| syn::parse_str::<LitInt>(&byte_str).unwrap());
 
     let gen = quote! {
-        impl #bevy_reflect_path::TypeUuid for #name {
+        impl #impl_generics #bevy_reflect_path::TypeUuid for #name #type_generics #where_clause {
             const TYPE_UUID: #bevy_reflect_path::Uuid = #bevy_reflect_path::Uuid::from_bytes([
                 #( #bytes ),*
             ]);

crates/bevy_reflect/src/type_uuid.rs

@@ -22,3 +22,25 @@ where
         std::any::type_name::<Self>()
     }
 }
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[derive(TypeUuid)]
+    #[uuid = "af6466c2-a9f4-11eb-bcbc-0242ac130002"]
+    struct TestDeriveStruct<T>
+    where
+        T: Clone,
+    {
+        _value: T,
+    }
+
+    fn test_impl_type_uuid(_: &impl TypeUuid) {}
+
+    #[test]
+    fn test_generic_type_uuid_derive() {
+        let test_struct = TestDeriveStruct { _value: 42 };
+        test_impl_type_uuid(&test_struct);
+    }
+}

crates/bevy_render/src/renderer/render_resource/render_resource.rs

@@ -273,3 +273,52 @@ impl RenderResources for bevy_transform::prelude::GlobalTransform {
         RenderResourceIterator::new(self)
     }
 }
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[derive(RenderResource, Bytes)]
+    #[as_crate(bevy_render)]
+    struct GenericRenderResource<T>
+    where
+        T: Bytes + Send + Sync + 'static,
+    {
+        value: T,
+    }
+
+    #[derive(RenderResources)]
+    #[as_crate(bevy_render)]
+    struct GenericRenderResources<T>
+    where
+        T: RenderResource + Send + Sync + 'static,
+    {
+        resource: T,
+    }
+
+    #[derive(Bytes, RenderResource, RenderResources)]
+    #[render_resources(from_self)]
+    #[as_crate(bevy_render)]
+    struct FromSelfGenericRenderResources<T>
+    where
+        T: Bytes + Send + Sync + 'static,
+    {
+        value: T,
+    }
+
+    fn test_impl_render_resource(_: &impl RenderResource) {}
+    fn test_impl_render_resources(_: &impl RenderResources) {}
+
+    #[test]
+    fn test_generic_render_resource_derive() {
+        let resource = GenericRenderResource { value: 42 };
+        test_impl_render_resource(&resource);
+
+        let resources = GenericRenderResources { resource };
+        test_impl_render_resources(&resources);
+
+        let from_self_resources = FromSelfGenericRenderResources { value: 42 };
+        test_impl_render_resource(&from_self_resources);
+        test_impl_render_resources(&from_self_resources);
+    }
+}