67aa2953d0
# Objective
In simple cases we might want to derive the `ExtractComponent` trait.
This adds symmetry to the existing `ExtractResource` derive.
## Solution
Add an implementation of `#[derive(ExtractComponent)]`.
The implementation is adapted from the existing `ExtractResource` derive macro.
Additionally, there is an attribute called `extract_component_filter`. This allows specifying a query filter type used when extracting.
If not specified, no filter (equal to `()`) is used.
So:
```rust
#[derive(Component, Clone, ExtractComponent)]
#[extract_component_filter(With<Fuel>)]
pub struct Car {
pub wheels: usize,
}
```
would expand to (a bit cleaned up here):
```rust
impl ExtractComponent for Car
{
type Query = &'static Self;
type Filter = With<Fuel>;
type Out = Self;
fn extract_component(item: QueryItem<'_, Self::Query>) -> Option<Self::Out> {
Some(item.clone())
}
}
```
---
## Changelog
- Added the ability to `#[derive(ExtractComponent)]` with an optional filter.
52 lines
1.5 KiB
Rust
52 lines
1.5 KiB
Rust
use proc_macro::TokenStream;
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use quote::quote;
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use syn::{parse_macro_input, parse_quote, DeriveInput, Path};
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pub fn derive_extract_component(input: TokenStream) -> TokenStream {
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let mut ast = parse_macro_input!(input as DeriveInput);
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let bevy_render_path: Path = crate::bevy_render_path();
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let bevy_ecs_path: Path = bevy_macro_utils::BevyManifest::default()
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.maybe_get_path("bevy_ecs")
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.expect("bevy_ecs should be found in manifest");
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ast.generics
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.make_where_clause()
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.predicates
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.push(parse_quote! { Self: Clone });
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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 filter = if let Some(attr) = ast
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.attrs
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.iter()
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.find(|a| a.path.is_ident("extract_component_filter"))
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{
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let filter = match attr.parse_args::<syn::Type>() {
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Ok(filter) => filter,
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Err(e) => return e.to_compile_error().into(),
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};
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quote! {
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#filter
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}
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} else {
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quote! {
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()
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}
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};
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TokenStream::from(quote! {
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impl #impl_generics #bevy_render_path::extract_component::ExtractComponent for #struct_name #type_generics #where_clause {
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type Query = &'static Self;
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type Filter = #filter;
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type Out = Self;
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fn extract_component(item: #bevy_ecs_path::query::QueryItem<'_, Self::Query>) -> Option<Self::Out> {
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Some(item.clone())
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}
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}
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})
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}
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