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use crate::utils::{AttrParams, DeriveType, State};
use convert_case::{Case, Casing};
use proc_macro2::TokenStream;
use quote::{format_ident, quote};
use syn::{DeriveInput, Fields, Result};
pub fn expand(input: &DeriveInput, trait_name: &'static str) -> Result<TokenStream> {
let state = State::with_attr_params(
input,
trait_name,
"is_variant".into(),
AttrParams {
enum_: vec!["ignore"],
variant: vec!["ignore"],
struct_: vec!["ignore"],
field: vec!["ignore"],
},
)?;
assert!(
state.derive_type == DeriveType::Enum,
"IsVariant can only be derived for enums",
);
let enum_name = &input.ident;
let (imp_generics, type_generics, where_clause) = input.generics.split_for_impl();
let mut funcs = vec![];
for variant_state in state.enabled_variant_data().variant_states {
let variant = variant_state.variant.unwrap();
let fn_name = format_ident!(
"is_{}",
variant.ident.to_string().to_case(Case::Snake),
span = variant.ident.span(),
);
let variant_ident = &variant.ident;
let data_pattern = match variant.fields {
Fields::Named(_) => quote! { {..} },
Fields::Unnamed(_) => quote! { (..) },
Fields::Unit => quote! {},
};
let variant_name = stringify!(variant_ident);
let func = quote! {
#[doc = "Returns `true` if this value is of type `"]
#[doc = #variant_name]
#[doc = "`. Returns `false` otherwise"]
pub const fn #fn_name(&self) -> bool {
match self {
#enum_name ::#variant_ident #data_pattern => true,
_ => false
}
}
};
funcs.push(func);
}
let imp = quote! {
#[automatically_derived]
impl #imp_generics #enum_name #type_generics #where_clause {
#(#funcs)*
}
};
Ok(imp)
}