use quote::format_ident;
use quote::quote;
use syn::{DeriveInput, Fields};
#[proc_macro_derive(EnumConstValue)]
pub fn enum_const_value(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
let derive_input: DeriveInput = syn::parse(input).unwrap();
let original_enum_type_name = &derive_input.ident;
let const_enum_type_ident = format_ident!("{}ConstValue", &original_enum_type_name);
let mut generate_const_enum = false;
let enum_data = proc_macro2_helper::enum_data(derive_input.data);
let retrieve_ident = enum_data
.iter()
.map(|variant| {
let ident = &variant.ident;
match variant.fields {
Fields::Unit => quote! {
Self::#ident => stringify!(#ident)
},
Fields::Unnamed(..) => quote! {
Self::#ident(_) => stringify!(#ident)
},
Fields::Named(..) => quote! {
Self::#ident { .. } => stringify!(#ident)
},
}
})
.collect::<Vec<_>>();
let mut generate_all_values = !retrieve_ident.is_empty();
let (idents_and_matcher, original_matcher): (Vec<_>, Vec<_>) = enum_data
.into_iter()
.enumerate()
.map(|(index, variant)| {
let index = index as i32;
let variant_name = variant.ident;
let tokens = match variant.fields {
Fields::Unit => {
quote! {}
},
Fields::Unnamed(..) => {
generate_const_enum = true;
generate_all_values = false;
quote! {
(..)
}
}
Fields::Named(..) => {
generate_const_enum = true;
generate_all_values = false;
quote! {
{..}
}
}
};
let original_enum_matcher = quote! {
&#original_enum_type_name::#variant_name #tokens => #index
};
let const_enum_matcher = quote! {
&#const_enum_type_ident::#variant_name => #index
};
((variant_name, const_enum_matcher), original_enum_matcher)
})
.unzip();
let (variant_names, const_matcher): (Vec<_>, Vec<_>) = idents_and_matcher.into_iter().unzip();
let tokens_all_values = if generate_all_values {
let number = variant_names.len();
quote! {
pub fn all_values() -> [Self; #number] {
[
#(Self::#variant_names),*
]
}
}
} else {
quote! {}
};
let mut tokens = quote! {
impl #original_enum_type_name {
#tokens_all_values
pub fn retrieve_ident(&self) -> &'static str {
match self {
#(#retrieve_ident),*
}
}
pub fn const_value(&self) -> i32 {
match self {
#(#original_matcher),*
}
}
}
};
if generate_const_enum {
tokens.extend(quote! {
pub enum #const_enum_type_ident {
#(#variant_names),*
}
impl #const_enum_type_ident {
pub fn value_for_variant(variant: &#const_enum_type_ident) -> i32 {
match variant {
#(#const_matcher),*
}
}
pub fn const_value(&self) -> i32 {
#const_enum_type_ident::value_for_variant(self)
}
}
});
}
tokens.into()
}