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[Merged by Bors] - Lift the 16-field limit from the SystemParam derive #6867

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[Merged by Bors] - Lift the 16-field limit from the SystemParam derive #6867

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d5d0a2a
relax 16-field limitation on `SystemParam` derive
JoJoJet Dec 6, 2022
768b8e1
add a test case
JoJoJet Dec 6, 2022
19da0e0
use a tuple impl for `get_param`
JoJoJet Dec 7, 2022
2c8518c
use field names for locals
JoJoJet Dec 7, 2022
c8d64f0
Merge remote-tracking branch 'upstream/main' into system-param-limit
JoJoJet Dec 12, 2022
17568f8
remove `field_indices`
JoJoJet Dec 14, 2022
5aabe45
Merge remote-tracking branch 'upstream/main' into system-param-limit
JoJoJet Dec 21, 2022
513afbf
cargo fmt
JoJoJet Dec 21, 2022
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22 changes: 19 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 @@ -10,7 +10,7 @@ use proc_macro2::Span;
use quote::{format_ident, quote};
use syn::{
parse::{Parse, ParseStream},
parse_macro_input,
parse_macro_input, parse_quote,
punctuated::Punctuated,
spanned::Spanned,
token::Comma,
Expand Down Expand Up @@ -416,6 +416,19 @@ pub fn derive_system_param(input: TokenStream) -> TokenStream {
_ => unreachable!(),
}));

let mut tuple_types: Vec<_> = field_types.iter().map(|x| quote! { #x }).collect();
let mut tuple_patterns: Vec<_> = fields.iter().map(|x| quote! { #x }).collect();

// If the number of fields exceeds the 16-parameter limit,
// fold the fields into tuples of tuples until we are below the limit.
const LIMIT: usize = 16;
while tuple_types.len() > LIMIT {
let end = Vec::from_iter(tuple_types.drain(..LIMIT));
tuple_types.push(parse_quote!( (#(#end,)*) ));
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It's a bit difficult to follow this but does this make a tuple of tuples? Wouldn't that just raise the limit to 256 instead of removing it?

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Oh wait I think I see what this is doing. My god this is going to have a lot of codgen for anything more than 32 entries, but you probably already should be expecting that with a ParamSet that big.


let end = Vec::from_iter(tuple_patterns.drain(..LIMIT));
tuple_patterns.push(parse_quote!( (#(#end,)*) ));
}
// Create a where clause for the `ReadOnlySystemParam` impl.
// Ensure that each field implements `ReadOnlySystemParam`.
let mut read_only_generics = generics.clone();
Expand All @@ -440,7 +453,7 @@ pub fn derive_system_param(input: TokenStream) -> TokenStream {

#[doc(hidden)]
type State<'w, 's, #punctuated_generic_idents> = FetchState<
(#(<#field_types as #path::system::SystemParam>::State,)*),
(#(<#tuple_types as #path::system::SystemParam>::State,)*),
#punctuated_generic_idents
>;

Expand Down Expand Up @@ -476,8 +489,11 @@ pub fn derive_system_param(input: TokenStream) -> TokenStream {
world: &'w #path::world::World,
change_tick: u32,
) -> Self::Item<'w, 's> {
let (#(#tuple_patterns,)*) = <
<(#(#tuple_types,)*) as #path::system::SystemParam>::State as #path::system::SystemParamState
>::get_param(&mut state.state, system_meta, world, change_tick);
#struct_name {
#(#fields: <<#field_types as #path::system::SystemParam>::State as #path::system::SystemParamState>::get_param(&mut state.state.#field_indices, system_meta, world, change_tick),)*
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#(#fields,)*
#(#ignored_fields: <#ignored_field_types>::default(),)*
}
}
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29 changes: 29 additions & 0 deletions crates/bevy_ecs/src/system/system_param.rs
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Expand Up @@ -1663,4 +1663,33 @@ mod tests {

#[derive(SystemParam)]
pub struct UnitParam {}

#[derive(Resource)]
pub struct R<const I: usize>;
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Any reason why you added this over re-using UnitParam?

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I want each field to be a distinct type, to make sure the derive macro doesn't mess up the order of the fields.


#[derive(SystemParam)]
pub struct LongParam<'w> {
_r0: Res<'w, R<0>>,
_r1: Res<'w, R<1>>,
_r2: Res<'w, R<2>>,
_r3: Res<'w, R<3>>,
_r4: Res<'w, R<4>>,
_r5: Res<'w, R<5>>,
_r6: Res<'w, R<6>>,
_r7: Res<'w, R<7>>,
_r8: Res<'w, R<8>>,
_r9: Res<'w, R<9>>,
_r10: Res<'w, R<10>>,
_r11: Res<'w, R<11>>,
_r12: Res<'w, R<12>>,
_r13: Res<'w, R<13>>,
_r14: Res<'w, R<14>>,
_r15: Res<'w, R<15>>,
_r16: Res<'w, R<16>>,
}

#[allow(dead_code)]
fn long_system(_param: LongParam) {
crate::system::assert_is_system(long_system);
}
}