bevy_asset_macros/
lib.rs

1// FIXME(15321): solve CI failures, then replace with `#![expect()]`.
2#![allow(missing_docs, reason = "Not all docs are written yet, see #3492.")]
3#![cfg_attr(docsrs, feature(doc_auto_cfg))]
4
5use bevy_macro_utils::BevyManifest;
6use proc_macro::{Span, TokenStream};
7use quote::{format_ident, quote};
8use syn::{parse_macro_input, Data, DeriveInput, Path};
9
10pub(crate) fn bevy_asset_path() -> Path {
11    BevyManifest::default().get_path("bevy_asset")
12}
13
14const DEPENDENCY_ATTRIBUTE: &str = "dependency";
15
16#[proc_macro_derive(Asset, attributes(dependency))]
17pub fn derive_asset(input: TokenStream) -> TokenStream {
18    let ast = parse_macro_input!(input as DeriveInput);
19    let bevy_asset_path: Path = bevy_asset_path();
20
21    let struct_name = &ast.ident;
22    let (impl_generics, type_generics, where_clause) = &ast.generics.split_for_impl();
23    let dependency_visitor = match derive_dependency_visitor_internal(&ast, &bevy_asset_path) {
24        Ok(dependency_visitor) => dependency_visitor,
25        Err(err) => return err.into_compile_error().into(),
26    };
27
28    TokenStream::from(quote! {
29        impl #impl_generics #bevy_asset_path::Asset for #struct_name #type_generics #where_clause { }
30        #dependency_visitor
31    })
32}
33
34#[proc_macro_derive(VisitAssetDependencies, attributes(dependency))]
35pub fn derive_asset_dependency_visitor(input: TokenStream) -> TokenStream {
36    let ast = parse_macro_input!(input as DeriveInput);
37    let bevy_asset_path: Path = bevy_asset_path();
38    match derive_dependency_visitor_internal(&ast, &bevy_asset_path) {
39        Ok(dependency_visitor) => TokenStream::from(dependency_visitor),
40        Err(err) => err.into_compile_error().into(),
41    }
42}
43
44fn derive_dependency_visitor_internal(
45    ast: &DeriveInput,
46    bevy_asset_path: &Path,
47) -> Result<proc_macro2::TokenStream, syn::Error> {
48    let struct_name = &ast.ident;
49    let (impl_generics, type_generics, where_clause) = &ast.generics.split_for_impl();
50
51    let visit_dep = |to_read| quote!(#bevy_asset_path::VisitAssetDependencies::visit_dependencies(#to_read, visit););
52    let is_dep_attribute = |a: &syn::Attribute| a.path().is_ident(DEPENDENCY_ATTRIBUTE);
53    let field_has_dep = |f: &syn::Field| f.attrs.iter().any(is_dep_attribute);
54
55    let body = match &ast.data {
56        Data::Struct(data_struct) => {
57            let fields = data_struct.fields.iter();
58            let field_visitors = fields.enumerate().filter(|(_, f)| field_has_dep(f));
59            let field_visitors = field_visitors.map(|(i, field)| match &field.ident {
60                Some(ident) => visit_dep(quote!(&self.#ident)),
61                None => {
62                    let index = syn::Index::from(i);
63                    visit_dep(quote!(&self.#index))
64                }
65            });
66            Some(quote!( #(#field_visitors)* ))
67        }
68        Data::Enum(data_enum) => {
69            let variant_has_dep = |v: &syn::Variant| v.fields.iter().any(field_has_dep);
70            let any_case_required = data_enum.variants.iter().any(variant_has_dep);
71            let cases = data_enum.variants.iter().filter(|v| variant_has_dep(v));
72            let cases = cases.map(|variant| {
73                let ident = &variant.ident;
74                let fields = &variant.fields;
75
76                let field_visitors = fields.iter().enumerate().filter(|(_, f)| field_has_dep(f));
77
78                let field_visitors = field_visitors.map(|(i, field)| match &field.ident {
79                    Some(ident) => visit_dep(quote!(#ident)),
80                    None => {
81                        let ident = format_ident!("member{i}");
82                        visit_dep(quote!(#ident))
83                    }
84                });
85                let fields = match fields {
86                    syn::Fields::Named(fields) => {
87                        let named = fields.named.iter().map(|f| f.ident.as_ref());
88                        quote!({ #(#named,)* .. })
89                    }
90                    syn::Fields::Unnamed(fields) => {
91                        let named = (0..fields.unnamed.len()).map(|i| format_ident!("member{i}"));
92                        quote!( ( #(#named,)* ) )
93                    }
94                    syn::Fields::Unit => unreachable!("Can't pass filter is_dep_attribute"),
95                };
96                quote!(Self::#ident #fields => {
97                    #(#field_visitors)*
98                })
99            });
100
101            any_case_required.then(|| quote!(match self { #(#cases)*, _ => {} }))
102        }
103        Data::Union(_) => {
104            return Err(syn::Error::new(
105                Span::call_site().into(),
106                "Asset derive currently doesn't work on unions",
107            ));
108        }
109    };
110
111    // prevent unused variable warning in case there are no dependencies
112    let visit = if body.is_none() {
113        quote! { _visit }
114    } else {
115        quote! { visit }
116    };
117
118    Ok(quote! {
119        impl #impl_generics #bevy_asset_path::VisitAssetDependencies for #struct_name #type_generics #where_clause {
120            fn visit_dependencies(&self, #visit: &mut impl FnMut(#bevy_asset_path::UntypedAssetId)) {
121                #body
122            }
123        }
124    })
125}
bevy_asset_macros/lib.rs

bevy_asset_macros/
lib.rs
