dcc03724a5
# Objective NOTE: This depends on #7267 and should not be merged until #7267 is merged. If you are reviewing this before that is merged, I highly recommend viewing the Base Sets commit instead of trying to find my changes amongst those from #7267. "Default sets" as described by the [Stageless RFC](https://github.com/bevyengine/rfcs/pull/45) have some [unfortunate consequences](https://github.com/bevyengine/bevy/discussions/7365). ## Solution This adds "base sets" as a variant of `SystemSet`: A set is a "base set" if `SystemSet::is_base` returns `true`. Typically this will be opted-in to using the `SystemSet` derive: ```rust #[derive(SystemSet, Clone, Hash, Debug, PartialEq, Eq)] #[system_set(base)] enum MyBaseSet { A, B, } ``` **Base sets are exclusive**: a system can belong to at most one "base set". Adding a system to more than one will result in an error. When possible we fail immediately during system-config-time with a nice file + line number. For the more nested graph-ey cases, this will fail at the final schedule build. **Base sets cannot belong to other sets**: this is where the word "base" comes from Systems and Sets can only be added to base sets using `in_base_set`. Calling `in_set` with a base set will fail. As will calling `in_base_set` with a normal set. ```rust app.add_system(foo.in_base_set(MyBaseSet::A)) // X must be a normal set ... base sets cannot be added to base sets .configure_set(X.in_base_set(MyBaseSet::A)) ``` Base sets can still be configured like normal sets: ```rust app.add_system(MyBaseSet::B.after(MyBaseSet::Ap)) ``` The primary use case for base sets is enabling a "default base set": ```rust schedule.set_default_base_set(CoreSet::Update) // this will belong to CoreSet::Update by default .add_system(foo) // this will override the default base set with PostUpdate .add_system(bar.in_base_set(CoreSet::PostUpdate)) ``` This allows us to build apis that work by default in the standard Bevy style. This is a rough analog to the "default stage" model, but it use the new "stageless sets" model instead, with all of the ordering flexibility (including exclusive systems) that it provides. --- ## Changelog - Added "base sets" and ported CoreSet to use them. ## Migration Guide TODO
85 lines
2.7 KiB
Rust
85 lines
2.7 KiB
Rust
use proc_macro::TokenStream;
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use quote::{quote, ToTokens};
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use syn::parse::{Parse, ParseStream};
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pub static SYSTEM_SET_ATTRIBUTE_NAME: &str = "system_set";
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pub static BASE_ATTRIBUTE_NAME: &str = "base";
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/// Derive a label trait
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///
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/// # Args
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///
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/// - `input`: The [`syn::DeriveInput`] for struct that is deriving the label trait
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/// - `trait_path`: The path [`syn::Path`] to the label trait
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pub fn derive_set(input: syn::DeriveInput, trait_path: &syn::Path) -> TokenStream {
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let ident = input.ident;
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let mut is_base = false;
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for attr in &input.attrs {
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if !attr
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.path
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.get_ident()
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.map_or(false, |ident| ident == SYSTEM_SET_ATTRIBUTE_NAME)
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{
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continue;
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}
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attr.parse_args_with(|input: ParseStream| {
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let meta = input.parse_terminated::<syn::Meta, syn::token::Comma>(syn::Meta::parse)?;
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for meta in meta {
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let ident = meta.path().get_ident().unwrap_or_else(|| {
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panic!(
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"Unrecognized attribute: `{}`",
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meta.path().to_token_stream()
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)
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});
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if ident == BASE_ATTRIBUTE_NAME {
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if let syn::Meta::Path(_) = meta {
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is_base = true;
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} else {
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panic!(
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"The `{BASE_ATTRIBUTE_NAME}` attribute is expected to have no value or arguments",
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);
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}
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} else {
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panic!(
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"Unrecognized attribute: `{}`",
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meta.path().to_token_stream()
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);
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}
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}
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Ok(())
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})
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.unwrap_or_else(|_| panic!("Invalid `{SYSTEM_SET_ATTRIBUTE_NAME}` attribute format"));
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}
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let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();
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let mut where_clause = where_clause.cloned().unwrap_or_else(|| syn::WhereClause {
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where_token: Default::default(),
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predicates: Default::default(),
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});
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where_clause.predicates.push(
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syn::parse2(quote! {
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Self: 'static + Send + Sync + Clone + Eq + ::std::fmt::Debug + ::std::hash::Hash
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})
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.unwrap(),
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);
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(quote! {
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impl #impl_generics #trait_path for #ident #ty_generics #where_clause {
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fn is_system_type(&self) -> bool {
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false
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}
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fn is_base(&self) -> bool {
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#is_base
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}
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fn dyn_clone(&self) -> std::boxed::Box<dyn #trait_path> {
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std::boxed::Box::new(std::clone::Clone::clone(self))
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}
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}
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})
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.into()
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}
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