extern crate proc_macro;
use proc_macro::TokenStream;
use quote::quote;
use syn::{
self,
DeriveInput,
TypeTuple,
};
#[proc_macro_attribute]
pub fn err_gen(attr: TokenStream, input: TokenStream) -> TokenStream {
use syn::Data::*;
let attr_ast: TypeTuple = syn::parse(attr).unwrap();
let input_ast: DeriveInput = syn::parse(input).unwrap();
let raw_enum = match input_ast.data {
Enum(data_enum) => data_enum,
_ => panic!("input must be an enum"),
};
let name = &input_ast.ident;
let mut nested_variants = quote! {};
for variant in raw_enum.variants.iter() {
let ident = &variant.ident;
nested_variants = match variant.attrs.get(0usize) {
Some(attr) => quote! {
#attr
#ident,
#nested_variants
},
None => quote! {
#ident,
#nested_variants
},
};
}
let enum_declaration = quote! {
#[derive(derive_more::Display, Debug)]
pub enum #name {
#nested_variants
ErrorNode(Box<dyn std::error::Error>),
}
impl std::error::Error for #name {}
};
let mut impl_clauses = quote! {};
for element in attr_ast.elems.iter() {
impl_clauses = quote! {
impl From<#element> for #name {
fn from(e: #element) -> Self { Self::ErrorNode(Box::new(e)) }
}
#impl_clauses
};
}
let result = quote! {
#enum_declaration
#impl_clauses
};
result.into()
}