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Error when #[entities] is on the wrong part #19445

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Error when #[entities] is on the wrong part #19445

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30 changes: 20 additions & 10 deletions crates/bevy_ecs/macros/src/component.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -92,12 +92,15 @@ pub fn derive_component(input: TokenStream) -> TokenStream {
Err(err) => err.into_compile_error().into(),
};

let map_entities = map_entities(
let map_entities = match map_entities(
&ast.data,
Ident::new("this", Span::call_site()),
relationship.is_some(),
relationship_target.is_some(),
).map(|map_entities_impl| quote! {
) {
Ok(map) => map,
Err(err) => return err.into_compile_error().into()
}.map(|map_entities_impl| quote! {
fn map_entities<M: #bevy_ecs_path::entity::EntityMapper>(this: &mut Self, mapper: &mut M) {
use #bevy_ecs_path::entity::MapEntities;
#map_entities_impl
Expand Down Expand Up @@ -308,7 +311,7 @@ pub(crate) fn map_entities(
self_ident: Ident,
is_relationship: bool,
is_relationship_target: bool,
) -> Option<TokenStream2> {
) -> Result<Option<TokenStream2>> {
match data {
Data::Struct(DataStruct { fields, .. }) => {
let mut map = Vec::with_capacity(fields.len());
Expand All @@ -334,16 +337,23 @@ pub(crate) fn map_entities(
map.push(quote!(#self_ident.#field_member.map_entities(mapper);));
});
if map.is_empty() {
return None;
return Ok(None);
};
Some(quote!(
Ok(Some(quote!(
#(#map)*
))
)))
}
Data::Enum(DataEnum { variants, .. }) => {
let mut map = Vec::with_capacity(variants.len());

for variant in variants.iter() {
if let Some(attr) = variant.attrs.iter().find(|a| a.path().is_ident(ENTITIES)) {
return Err(syn::Error::new(
attr.span(),
"`#[entities]` should be on the associated type, not on the variant.",
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Not a fan of this message - it only applies for tuple variants. How about "entities should be on the fields in the enum variant, not on the variant"?

));
}

let field_members = variant
.fields
.iter()
Expand Down Expand Up @@ -371,17 +381,17 @@ pub(crate) fn map_entities(
}

if map.is_empty() {
return None;
return Ok(None);
};

Some(quote!(
Ok(Some(quote!(
match #self_ident {
#(#map,)*
_ => {}
}
))
)))
}
Data::Union(_) => None,
Data::Union(_) => Ok(None),
}
}

Expand Down
8 changes: 5 additions & 3 deletions crates/bevy_ecs/macros/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -191,13 +191,15 @@ pub fn derive_bundle(input: TokenStream) -> TokenStream {
pub fn derive_map_entities(input: TokenStream) -> TokenStream {
let ast = parse_macro_input!(input as DeriveInput);
let ecs_path = bevy_ecs_path();

let map_entities_impl = map_entities(
let map_entities_impl = match map_entities(
&ast.data,
Ident::new("self", Span::call_site()),
false,
false,
);
) {
Ok(map) => map,
Err(err) => return err.into_compile_error().into(),
};

let struct_name = &ast.ident;
let (impl_generics, type_generics, where_clause) = &ast.generics.split_for_impl();
Expand Down