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extern crate quote;
extern crate proc_macro2;
extern crate syn;
use proc_macro::TokenStream;
use proc_macro2::TokenStream as TokenStream2;
use proc_macro2::TokenTree as TokenTree2;
use std::str::FromStr;
use std::any::type_name;
use quote::quote;
/// See `gen_random::GenRandom`.
#[proc_macro_derive(GenRandom, attributes(prob, scale, bias, params, only_if))]
pub fn gen_random_derive(input: TokenStream) -> TokenStream {
// Construct a representation of Rust code as a syntax tree
// that we can manipulate
let ast = syn::parse(input).unwrap();
// Build the trait implementation
impl_gen_random(&ast)
}
fn get_attribute(attrs: &[syn::Attribute], name: &str) -> Option<TokenStream2> {
let attr = attrs.iter().find(|a| {
let path = &a.path;
if let Some(ident) = path.get_ident() {
ident == name
} else {
false
}
})?;
let tokens: TokenStream2 = attr.tokens.clone().into();
let tokens: Vec<TokenTree2> = tokens.into_iter().collect();
if tokens.len() != 1 {
panic!("Expected {name}(<value>)");
}
use TokenTree2::Group;
use proc_macro2::Delimiter;
let value = match &tokens[0] {
Group(g) if g.delimiter() == Delimiter::Parenthesis => {
g.stream()
},
_ => {
panic!("Expected {name}(<value>)");
},
};
Some(value)
}
fn parse_attribute_value<T: FromStr>(attrs: &[syn::Attribute], name: &str) -> Option<T> {
let stream = get_attribute(attrs, name)?;
let Ok(value) = stream.to_string().parse() else {
panic!("Bad {} for {name} attribute", type_name::<T>())
};
Some(value)
}
fn generate_fields(fields: &syn::Fields, params_type: &TokenStream2) -> impl quote::ToTokens {
let mut field_values = quote! {};
for field in fields.iter() {
if let Some(name) = &field.ident {
field_values.extend(quote! {#name: });
}
let ty = &field.ty;
field_values.extend(quote! { <#ty as GenRandom<#params_type>>::gen_random_params(rng, <#params_type as GenRandomParams>::inc_depth(params)) });
if let Some(scale) = get_attribute(&field.attrs, "scale") {
field_values.extend(quote! { * ( #scale ) });
}
if let Some(bias) = get_attribute(&field.attrs, "bias") {
field_values.extend(quote! { + ( #bias ) });
}
field_values.extend(quote! { , });
}
// surround the field values with either () or {} brackets
match fields {
syn::Fields::Named(_) => {
Some(proc_macro2::Group::new(
proc_macro2::Delimiter::Brace,
field_values
))
},
syn::Fields::Unnamed(_) => {
Some(proc_macro2::Group::new(
proc_macro2::Delimiter::Parenthesis,
field_values
))
},
syn::Fields::Unit => None,
}
}
fn impl_gen_random(ast: &syn::DeriveInput) -> TokenStream {
let name = &ast.ident;
let mut function_body;
let params_type = get_attribute(&ast.attrs, "params").unwrap_or(quote! { () });
match &ast.data {
syn::Data::Enum(enumeration) => {
let variants = &enumeration.variants;
function_body = quote! {
let mut prob_sum = 0.0;
};
for variant in variants.iter() {
match parse_attribute_value::<f64>(&variant.attrs, "prob") {
Some(prob) => if prob >= 0.0 {
let only_if = get_attribute(&variant.attrs, "only_if")
.unwrap_or(quote! { true });
function_body.extend(quote! {
if #only_if { prob_sum += #prob; }
});
} else {
panic!("Variant {} has negative probability", variant.ident)
},
None => panic!("Variant {} has no probability", variant.ident)
}
}
let compensation = (variants.len() + 1) as f64 * f64::EPSILON;
function_body.extend(quote! {
let mut variant: f64 = rng.gen_range(0.0..prob_sum - #compensation);
});
// parse enum fields
for variant in variants.iter() {
// Note: None case was checked above when computing prob_sum
let probability: f64 = parse_attribute_value(&variant.attrs, "prob").unwrap();
let only_if = get_attribute(&variant.attrs, "only_if")
.unwrap_or(quote! { true });
let name = &variant.ident;
let field_values = generate_fields(&variant.fields, ¶ms_type);
function_body.extend(quote! {
if #only_if {
variant -= #probability;
if variant < 0.0 { return Self::#name #field_values; }
}
});
}
function_body.extend(quote! {
panic!("RNG returned value outside of range (this should never happen).")
});
},
syn::Data::Struct(structure) => {
let field_values = generate_fields(&structure.fields, ¶ms_type);
function_body = quote! {
Self #field_values
};
},
syn::Data::Union(_) => panic!("derive(GenRandom) cannot be applied to unions."),
};
let gen = quote! {
impl GenRandom<#params_type> for #name {
fn gen_random_params(rng: &mut impl rand::Rng, params: #params_type) -> Self {
#function_body
}
}
};
//println!("{gen}");
gen.into()
}
|
