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use proc_macro2::TokenStream;
use quote::ToTokens;
use std::ops::Deref;
use syn::{
parse::{Parse, ParseStream},
Error, Fields, Ident, ItemEnum, Result, Type,
};
pub struct EnumData {
repr: ItemEnum,
field_types: Vec<Type>,
}
impl EnumData {
pub fn field_types(&self) -> impl ExactSizeIterator<Item = &Type> + Clone {
self.field_types.iter()
}
pub fn variant_idents(&self) -> impl ExactSizeIterator<Item = &Ident> + Clone {
self.variants.iter().map(|v| &v.ident)
}
}
impl Deref for EnumData {
type Target = ItemEnum;
fn deref(&self) -> &Self::Target {
&self.repr
}
}
impl From<EnumData> for ItemEnum {
fn from(other: EnumData) -> Self {
other.repr
}
}
impl Parse for EnumData {
fn parse(input: ParseStream<'_>) -> Result<Self> {
let item: ItemEnum = input.parse()?;
if item.variants.is_empty() {
return Err(Error::new(
item.brace_token.span,
"may not be used on enums without variants",
));
}
let field_types = item.variants.iter().try_fold(
Vec::with_capacity(item.variants.len()),
|mut field_types, v| {
if let Some((_, e)) = &v.discriminant {
return Err(error!(e, "may not be used on enums with discriminants"));
}
if v.fields.is_empty() {
return Err(error!(
v,
"may not be used on enums with variants with zero fields"
));
} else if v.fields.len() != 1 {
return Err(error!(
v,
"may not be used on enums with variants with multiple fields"
));
}
match &v.fields {
Fields::Unnamed(f) => {
field_types.push(f.unnamed.iter().next().unwrap().ty.clone());
Ok(field_types)
}
Fields::Named(_) => {
Err(error!(v, "may not be used on enums with variants with named fields"))
}
Fields::Unit => unreachable!(),
}
},
)?;
Ok(Self { repr: item, field_types })
}
}
impl ToTokens for EnumData {
fn to_tokens(&self, tokens: &mut TokenStream) {
self.repr.to_tokens(tokens)
}
}