derive(SystemParam) better lifetime param (#10331)

crates/bevy_ecs/macros/src/lib.rs

@@ -17,7 +17,7 @@ use proc_macro2::Span;
 use quote::{format_ident, quote};
 use syn::{
     parse_macro_input, parse_quote, punctuated::Punctuated, spanned::Spanned, token::Comma,
-    ConstParam, DeriveInput, GenericParam, Ident, Index, TypeParam,
+    visit_mut::VisitMut, ConstParam, DeriveInput, GenericParam, Ident, Index, TypeParam,
 };
 
 enum BundleFieldKind {
@@ -274,9 +274,37 @@ pub fn impl_param_set(_input: TokenStream) -> TokenStream {
     tokens
 }
 
+// replace 'world with 'w and 'state with 's
+fn replace_lifetimes(stream: TokenStream, f: Box<dyn Fn(&str) -> &str>) -> TokenStream {
+    struct LifetimeReplacer {
+        f: Box<dyn Fn(&str) -> &str>,
+    }
+    impl VisitMut for LifetimeReplacer {
+        fn visit_lifetime_mut(&mut self, lifetime: &mut syn::Lifetime) {
+            lifetime.ident = syn::Ident::new(
+                (self.f)(lifetime.ident.to_string().as_str()),
+                lifetime.ident.span(),
+            );
+        }
+    }
+
+    let mut ast = parse_macro_input!(stream as DeriveInput);
+    LifetimeReplacer { f }.visit_derive_input_mut(&mut ast);
+
+    quote! {#ast}.into()
+}
+
 /// Implement `SystemParam` to use a struct as a parameter in a system
 #[proc_macro_derive(SystemParam, attributes(system_param))]
 pub fn derive_system_param(input: TokenStream) -> TokenStream {
+    let input = replace_lifetimes(
+        input,
+        Box::new(|s| match s {
+            "world" => "w",
+            "state" => "s",
+            other => other,
+        }),
+    );
     let token_stream = input.clone();
     let ast = parse_macro_input!(input as DeriveInput);
     let syn::Data::Struct(syn::DataStruct {
@@ -321,7 +349,8 @@ pub fn derive_system_param(input: TokenStream) -> TokenStream {
                 lt,
                 r#"invalid lifetime name: expected `'w` or `'s`
  'w -- refers to data stored in the World.
- 's -- refers to data stored in the SystemParam's state.'"#,
+ 's -- refers to data stored in the SystemParam's state.
+ using `'world` or `'state` is permitted aswell"#,
             )
             .into_compile_error()
             .into();

crates/bevy_ecs/src/system/system_param.rs

@@ -36,6 +36,7 @@ use std::{
 ///
 /// Derived `SystemParam` structs may have two lifetimes: `'w` for data stored in the [`World`],
 /// and `'s` for data stored in the parameter's state.
+/// instead of `'w` and `'s`, you are permitted to use `'world` and `'state`
 ///
 /// The following list shows the most common [`SystemParam`]s and which lifetime they require
 ///
@@ -124,6 +125,28 @@ use std::{
 ///   by [`SystemParam::get_param`] with the provided [`system_meta`](SystemMeta).
 /// - None of the world accesses may conflict with any prior accesses registered
 ///   on `system_meta`.
+///
+/// Doc test to ensure that 'world and 'state are permitted aswell
+/// ```
+/// # use bevy_ecs::prelude::*;
+/// # #[derive(Resource)]
+/// # struct SomeResource;
+/// # #[derive(Event)]
+/// # struct SomeEvent;
+/// # #[derive(Resource)]
+/// # struct SomeOtherResource;
+/// # use bevy_ecs::system::SystemParam;
+/// # #[derive(SystemParam)]
+/// # struct ParamsExample<'world, 'state> {
+/// #    query: Query<'world, 'state, Entity>,
+/// #    res: Res<'world, SomeResource>,
+/// #    res_mut: ResMut<'world, SomeOtherResource>,
+/// #    world: Local<'state, u8>,
+/// #    commands: Commands<'world, 'state>,
+/// #    eventreader: EventReader<'world, 'state, SomeEvent>,
+/// #    eventwriter: EventWriter<'world, SomeEvent>
+/// # }
+/// ```
 pub unsafe trait SystemParam: Sized {
     /// Used to store data which persists across invocations of a system.
     type State: Send + Sync + 'static;

crates/bevy_macro_utils/Cargo.toml

@@ -12,7 +12,7 @@ keywords = ["bevy"]
 toml_edit = { version = "0.22.7", default-features = false, features = [
   "parse",
 ] }
-syn = "2.0"
+syn = { version = "2.0", features = ["visit-mut"] }
 quote = "1.0"
 proc-macro2 = "1.0"