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use proc_macro2::{Ident, Literal, TokenStream};
use quote::quote;
use syn::{DataEnum, Variant};
use super::generate_fields;
fn variant_weight(variant: &Variant) -> Literal {
for attr in variant.attrs.iter() {
if attr.path.is_ident("weight") {
return attr.parse_args::<Literal>().expect("expected literal for `#[weight(...)]`")
}
}
Literal::u64_suffixed(1)
}
pub fn generate(name: &Ident, ty: DataEnum) -> TokenStream {
let mut variant_weights = ty.variants.into_iter()
.map(|variant| (variant_weight(&variant), variant));
let mut arms = TokenStream::new();
let mut total_weight = quote! { 0 };
if let Some((weight, variant)) = variant_weights.next() {
let variant_name = variant.ident;
let fields = generate_fields(variant.fields);
arms.extend(quote! {
let end = #weight;
if 0 <= value && value < end {
return Self::#variant_name #fields
}
});
total_weight = quote! { #weight };
for (weight, variant) in variant_weights {
let variant_name = variant.ident;
let fields = generate_fields(variant.fields);
arms.extend(quote! {
let start = end;
let end = start + #weight;
if start <= value && value < end {
return Self::#variant_name #fields
}
});
total_weight = quote! { #total_weight + #weight };
}
}
quote! {
impl generate_random::GenerateRandom for #name {
fn generate_random<R: rand::Rng + ?Sized>(rng: &mut R) -> Self {
let total_weight = #total_weight;
let value = rng.gen_range(0..total_weight);
#arms
unreachable!()
}
}
}
}
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