bevy_asset_macros/
lib.rs

1#![cfg_attr(docsrs, feature(doc_cfg))]
2
3//! Macros for deriving asset traits.
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::shared().get_path("bevy_asset")
12}
13
14const DEPENDENCY_ATTRIBUTE: &str = "dependency";
15
16/// Implement the `Asset` trait.
17#[proc_macro_derive(Asset, attributes(dependency))]
18pub fn derive_asset(input: TokenStream) -> TokenStream {
19    let ast = parse_macro_input!(input as DeriveInput);
20    let bevy_asset_path: Path = bevy_asset_path();
21
22    let struct_name = &ast.ident;
23    let (impl_generics, type_generics, where_clause) = &ast.generics.split_for_impl();
24    let dependency_visitor = match derive_dependency_visitor_internal(&ast, &bevy_asset_path) {
25        Ok(dependency_visitor) => dependency_visitor,
26        Err(err) => return err.into_compile_error().into(),
27    };
28
29    TokenStream::from(quote! {
30        impl #impl_generics #bevy_asset_path::Asset for #struct_name #type_generics #where_clause { }
31        #dependency_visitor
32    })
33}
34
35/// Implement the `VisitAssetDependencies` trait.
36#[proc_macro_derive(VisitAssetDependencies, attributes(dependency))]
37pub fn derive_asset_dependency_visitor(input: TokenStream) -> TokenStream {
38    let ast = parse_macro_input!(input as DeriveInput);
39    let bevy_asset_path: Path = bevy_asset_path();
40    match derive_dependency_visitor_internal(&ast, &bevy_asset_path) {
41        Ok(dependency_visitor) => TokenStream::from(dependency_visitor),
42        Err(err) => err.into_compile_error().into(),
43    }
44}
45
46fn derive_dependency_visitor_internal(
47    ast: &DeriveInput,
48    bevy_asset_path: &Path,
49) -> Result<proc_macro2::TokenStream, syn::Error> {
50    let struct_name = &ast.ident;
51    let (impl_generics, type_generics, where_clause) = &ast.generics.split_for_impl();
52
53    let visit_dep = |to_read| quote!(#bevy_asset_path::VisitAssetDependencies::visit_dependencies(#to_read, visit););
54    let is_dep_attribute = |a: &syn::Attribute| a.path().is_ident(DEPENDENCY_ATTRIBUTE);
55    let field_has_dep = |f: &syn::Field| f.attrs.iter().any(is_dep_attribute);
56
57    let body = match &ast.data {
58        Data::Struct(data_struct) => {
59            let fields = data_struct.fields.iter();
60            let field_visitors = fields.enumerate().filter(|(_, f)| field_has_dep(f));
61            let field_visitors = field_visitors.map(|(i, field)| match &field.ident {
62                Some(ident) => visit_dep(quote!(&self.#ident)),
63                None => {
64                    let index = syn::Index::from(i);
65                    visit_dep(quote!(&self.#index))
66                }
67            });
68            Some(quote!( #(#field_visitors)* ))
69        }
70        Data::Enum(data_enum) => {
71            let variant_has_dep = |v: &syn::Variant| v.fields.iter().any(field_has_dep);
72            let any_case_required = data_enum.variants.iter().any(variant_has_dep);
73            let cases = data_enum.variants.iter().filter(|v| variant_has_dep(v));
74            let cases = cases.map(|variant| {
75                let ident = &variant.ident;
76                let fields = &variant.fields;
77
78                let field_visitors = fields.iter().enumerate().filter(|(_, f)| field_has_dep(f));
79
80                let field_visitors = field_visitors.map(|(i, field)| match &field.ident {
81                    Some(ident) => visit_dep(quote!(#ident)),
82                    None => {
83                        let ident = format_ident!("member{i}");
84                        visit_dep(quote!(#ident))
85                    }
86                });
87                let fields = match fields {
88                    syn::Fields::Named(fields) => {
89                        let named = fields.named.iter().map(|f| f.ident.as_ref());
90                        quote!({ #(#named,)* .. })
91                    }
92                    syn::Fields::Unnamed(fields) => {
93                        let named = (0..fields.unnamed.len()).map(|i| format_ident!("member{i}"));
94                        quote!( ( #(#named,)* ) )
95                    }
96                    syn::Fields::Unit => unreachable!("Can't pass filter is_dep_attribute"),
97                };
98                quote!(Self::#ident #fields => {
99                    #(#field_visitors)*
100                })
101            });
102
103            any_case_required.then(|| quote!(match self { #(#cases)*, _ => {} }))
104        }
105        Data::Union(_) => {
106            return Err(syn::Error::new(
107                Span::call_site().into(),
108                "Asset derive currently doesn't work on unions",
109            ));
110        }
111    };
112
113    // prevent unused variable warning in case there are no dependencies
114    let visit = if body.is_none() {
115        quote! { _visit }
116    } else {
117        quote! { visit }
118    };
119
120    Ok(quote! {
121        impl #impl_generics #bevy_asset_path::VisitAssetDependencies for #struct_name #type_generics #where_clause {
122            fn visit_dependencies(&self, #visit: &mut impl FnMut(#bevy_asset_path::UntypedAssetId)) {
123                #body
124            }
125        }
126    })
127}
bevy_asset_macros/lib.rs

bevy_asset_macros/
lib.rs
