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#![recursion_limit = "128"]
#![deny(warnings)]
extern crate proc_macro;
use proc_macro2::{Span, TokenStream};
use quote::{quote, ToTokens};
use std::fmt::{Display, self};
use syn::{Ident, DeriveInput};
#[proc_macro_derive(IntoEnumIterator)]
pub fn into_enum_iterator(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
derive(input).unwrap_or_else(|e| e.to_compile_error()).into()
}
fn derive(input: proc_macro::TokenStream) -> Result<TokenStream, syn::Error> {
let ast = syn::parse::<DeriveInput>(input)?;
if !ast.generics.params.is_empty() {
return Err(Error::GenericsUnsupported.with_tokens(&ast.generics));
}
let ty = &ast.ident;
let vis = &ast.vis;
let ty_doc = format!("Iterator over the variants of {}", ty);
let iter_ty = Ident::new(&(ty.to_string() + "EnumIterator"), Span::call_site());
let variants = match &ast.data {
syn::Data::Enum(e) => &e.variants,
_ => return Err(Error::ExpectedEnum.with_tokens(&ast)),
};
let arms = variants.iter().enumerate()
.map(|(idx, v)| {
let id = &v.ident;
match v.fields {
syn::Fields::Unit => Ok(quote! { #idx => #ty::#id, }),
_ => Err(Error::ExpectedUnitVariant.with_tokens(v)),
}
})
.collect::<Result<Vec<_>, _>>()?;
let nb_variants = arms.len();
let tokens = quote! {
#[doc = #ty_doc]
#[derive(Clone, Copy, Debug)]
#vis struct #iter_ty {
idx: usize,
}
impl ::core::iter::Iterator for #iter_ty {
type Item = #ty;
fn next(&mut self) -> ::core::option::Option<Self::Item> {
let id = match self.idx {
#(#arms)*
_ => return ::core::option::Option::None,
};
self.idx += 1;
::core::option::Option::Some(id)
}
fn size_hint(&self) -> (usize, ::core::option::Option<usize>) {
let n = #nb_variants - self.idx;
(n, ::core::option::Option::Some(n))
}
}
impl ::core::iter::ExactSizeIterator for #iter_ty {}
impl ::core::iter::FusedIterator for #iter_ty {}
impl ::enum_iterator::IntoEnumIterator for #ty {
type Iterator = #iter_ty;
const VARIANT_COUNT: usize = #nb_variants;
fn into_enum_iter() -> Self::Iterator {
#iter_ty { idx: 0 }
}
}
};
let tokens = quote! {
const _: () = {
#tokens
};
};
Ok(tokens)
}
#[derive(Debug)]
enum Error {
ExpectedEnum,
ExpectedUnitVariant,
GenericsUnsupported,
}
impl Error {
fn with_tokens<T: ToTokens>(self, tokens: T) -> syn::Error {
syn::Error::new_spanned(tokens, self)
}
}
impl Display for Error {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
match self {
Error::ExpectedEnum =>
f.write_str("IntoEnumIterator can only be derived for enum types"),
Error::ExpectedUnitVariant =>
f.write_str("IntoEnumIterator can only be derived for enum types with unit \
variants only"),
Error::GenericsUnsupported =>
f.write_str("IntoEnumIterator cannot be derived for generic types"),
}
}
}