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derive asset for enums (#10410)
# Objective allow deriving `Asset` for enums, and for tuple structs. ## Solution add to the proc macro, generating visitor calls to the variant's data (if required). supports unnamed or named field variants, and struct variants when the struct also derives `Asset`: ```rust #[derive(Asset, TypePath)] pub enum MyAssetEnum { Unnamed ( #[dependency] Handle<Image> ), Named { #[dependency] array_handle: Handle<Image>, #[dependency] atlas_handles: Vec<Handle<Image>>, }, StructStyle( #[dependency] VariantStruct ), Empty, } #[derive(Asset, TypePath)] pub struct VariantStruct { // ... } ``` also extend the struct implementation to support tuple structs: ```rust #[derive(Asset, TypePath)] pub struct MyImageNewtype( #[dependency] Handle<Image> ); ```` --------- Co-authored-by: Nicola Papale <nico@nicopap.ch>
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24b4c517d0
commit
5581926ad3
2 changed files with 94 additions and 25 deletions
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@ -1,6 +1,6 @@
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use bevy_macro_utils::BevyManifest;
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use proc_macro::{Span, TokenStream};
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use quote::quote;
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use quote::{format_ident, quote};
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use syn::{parse_macro_input, Data, DeriveInput, Path};
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pub(crate) fn bevy_asset_path() -> syn::Path {
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@ -41,33 +41,71 @@ fn derive_dependency_visitor_internal(
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ast: &DeriveInput,
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bevy_asset_path: &Path,
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) -> Result<proc_macro2::TokenStream, syn::Error> {
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let mut field_visitors = Vec::new();
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if let Data::Struct(data_struct) = &ast.data {
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for field in &data_struct.fields {
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if field
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.attrs
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.iter()
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.any(|a| a.path().is_ident(DEPENDENCY_ATTRIBUTE))
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{
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if let Some(field_ident) = &field.ident {
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field_visitors.push(quote! {
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#bevy_asset_path::VisitAssetDependencies::visit_dependencies(&self.#field_ident, visit);
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});
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}
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}
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}
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} else {
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return Err(syn::Error::new(
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Span::call_site().into(),
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"Asset derive currently only works on structs",
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));
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}
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let struct_name = &ast.ident;
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let (impl_generics, type_generics, where_clause) = &ast.generics.split_for_impl();
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let visit_dep = |to_read| quote!(#bevy_asset_path::VisitAssetDependencies::visit_dependencies(#to_read, visit););
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let is_dep_attribute = |a: &syn::Attribute| a.path().is_ident(DEPENDENCY_ATTRIBUTE);
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let field_has_dep = |f: &syn::Field| f.attrs.iter().any(is_dep_attribute);
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let body = match &ast.data {
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Data::Struct(data_struct) => {
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let fields = data_struct.fields.iter();
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let field_visitors = fields.enumerate().filter(|(_, f)| field_has_dep(f));
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let field_visitors = field_visitors.map(|(i, field)| match &field.ident {
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Some(ident) => visit_dep(quote!(&self.#ident)),
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None => {
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let index = syn::Index::from(i);
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visit_dep(quote!(&self.#index))
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}
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});
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Some(quote!( #(#field_visitors)* ))
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}
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Data::Enum(data_enum) => {
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let variant_has_dep = |v: &syn::Variant| v.fields.iter().any(field_has_dep);
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let any_case_required = data_enum.variants.iter().any(variant_has_dep);
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let cases = data_enum.variants.iter().filter(|v| variant_has_dep(v));
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let cases = cases.map(|variant| {
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let ident = &variant.ident;
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let fields = &variant.fields;
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let field_visitors = fields.iter().enumerate().filter(|(_, f)| field_has_dep(f));
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let field_visitors = field_visitors.map(|(i, field)| match &field.ident {
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Some(ident) => visit_dep(quote!(#ident)),
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None => {
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let ident = format_ident!("member{i}");
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visit_dep(quote!(#ident))
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}
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});
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let fields = match fields {
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syn::Fields::Named(fields) => {
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let named = fields.named.iter().map(|f| f.ident.as_ref());
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quote!({ #(#named,)* .. })
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}
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syn::Fields::Unnamed(fields) => {
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let named = (0..fields.unnamed.len()).map(|i| format_ident!("member{i}"));
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quote!( ( #(#named,)* ) )
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}
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syn::Fields::Unit => unreachable!("Can't pass filter is_dep_attribute"),
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};
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quote!(Self::#ident #fields => {
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#(#field_visitors)*
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})
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});
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any_case_required.then(|| quote!(match self { #(#cases)*, _ => {} }))
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}
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Data::Union(_) => {
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return Err(syn::Error::new(
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Span::call_site().into(),
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"Asset derive currently doesn't work on unions",
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));
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}
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};
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// prevent unused variable warning in case there are no dependencies
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let visit = if field_visitors.is_empty() {
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let visit = if body.is_none() {
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quote! { _visit }
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} else {
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quote! { visit }
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@ -76,7 +114,7 @@ fn derive_dependency_visitor_internal(
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Ok(quote! {
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impl #impl_generics #bevy_asset_path::VisitAssetDependencies for #struct_name #type_generics #where_clause {
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fn visit_dependencies(&self, #visit: &mut impl FnMut(#bevy_asset_path::UntypedAssetId)) {
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#(#field_visitors)*
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#body
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}
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}
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})
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@ -1180,4 +1180,35 @@ mod tests {
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// running schedule does not error on ambiguity between the 2 uses_assets systems
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app.world.run_schedule(Update);
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}
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// validate the Asset derive macro for various asset types
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#[derive(Asset, TypePath)]
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pub struct TestAsset;
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#[allow(dead_code)]
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#[derive(Asset, TypePath)]
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pub enum EnumTestAsset {
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Unnamed(#[dependency] Handle<TestAsset>),
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Named {
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#[dependency]
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handle: Handle<TestAsset>,
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#[dependency]
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vec_handles: Vec<Handle<TestAsset>>,
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#[dependency]
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embedded: TestAsset,
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},
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StructStyle(#[dependency] TestAsset),
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Empty,
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}
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#[derive(Asset, TypePath)]
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pub struct StructTestAsset {
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#[dependency]
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handle: Handle<TestAsset>,
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#[dependency]
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embedded: TestAsset,
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}
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#[derive(Asset, TypePath)]
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pub struct TupleTestAsset(#[dependency] Handle<TestAsset>);
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}
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