enum_traits_macros 4.0.0

Procedural macros adding functionality to enums. Derives traits from the crate `enum_traits`
Documentation 
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use crate::util;
use proc_macro2::TokenStream;
use syn::{Ident,Variant};

fn variant_unit_ident(variant: &Variant) -> &Ident{
	util::variant_unit_ident(variant,"EnumStep")
}

pub fn gen_impl(item: syn::ItemEnum) -> TokenStream{
	let (impl_generics,ty_generics,where_clause) = item.generics.split_for_impl();
	let ident = item.ident;

	let prev_match_arms = {
			let iter = item.variants.iter().rev().map(variant_unit_ident);
			iter.zip(item.variants.iter().rev().map(variant_unit_ident).skip(1))
		}.map(|(variant_ident1,variant_ident2)|{
			quote! { #ident::#variant_ident1 => #ident::#variant_ident2, }
		});

	let next_match_arms = {
			let iter = item.variants.iter().map(variant_unit_ident);
			iter.zip(item.variants.iter().map(variant_unit_ident).skip(1))
		}.map(|(variant_ident1,variant_ident2)|{
			quote! { #ident::#variant_ident1 => #ident::#variant_ident2, }
		});

	{
		let fn_next = quote!{
			#[inline]
			#[allow(unreachable_code)]
			fn next(self) -> ::core::option::Option<Self>{
				::core::option::Option::Some(match self{
					#( #next_match_arms )*
					_ => return ::core::option::Option::None
				})
			}
		};

		let fn_prev = quote!{
			#[inline]
			#[allow(unreachable_code)]
			fn previous(self) -> ::core::option::Option<Self>{
				::core::option::Option::Some(match self{
					#( #prev_match_arms )*
					_ => return ::core::option::Option::None
				})
			}
		};

		quote!{
			#[automatically_derived]
			impl #impl_generics ::enum_traits::Step for #ident #ty_generics #where_clause{
				#fn_next
				#fn_prev
			}
		}
	}
}