9733613c07
# Objective Base sets, added in #7466 are a special type of system set. Systems can only be added to base sets via `in_base_set`, while non-base sets can only be added via `in_set`. Unfortunately this is currently guarded by a runtime panic, which presents an unfortunate toe-stub when the wrong method is used. The delayed response between writing code and encountering the error (possibly hours) makes the distinction between base sets and other sets much more difficult to learn. ## Solution Add the marker traits `BaseSystemSet` and `FreeSystemSet`. `in_base_set` and `in_set` now respectively accept these traits, which moves the runtime panic to a compile time error. --- ## Changelog + Added the marker trait `BaseSystemSet`, which is distinguished from a `FreeSystemSet`. These are both subtraits of `SystemSet`. ## Migration Guide None if merged with 0.10
101 lines
3.3 KiB
Rust
101 lines
3.3 KiB
Rust
use proc_macro::TokenStream;
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use quote::{format_ident, 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 set trait
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///
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/// # Args
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///
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/// - `input`: The [`syn::DeriveInput`] for the struct that we want to derive the set trait for
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/// - `trait_path`: The [`syn::Path`] to the set trait
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pub fn derive_set(input: syn::DeriveInput, trait_path: &syn::Path) -> TokenStream {
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let mut base_trait_path = trait_path.clone();
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let ident = &mut base_trait_path.segments.last_mut().unwrap().ident;
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*ident = format_ident!("Base{ident}");
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let mut free_trait_path = trait_path.clone();
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let ident = &mut free_trait_path.segments.last_mut().unwrap().ident;
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*ident = format_ident!("Free{ident}");
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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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let marker_impl = if is_base {
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quote! {
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impl #impl_generics #base_trait_path for #ident #ty_generics #where_clause {}
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}
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} else {
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quote! {
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impl #impl_generics #free_trait_path for #ident #ty_generics #where_clause {}
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}
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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_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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#marker_impl
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})
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.into()
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}
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