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#[macro_use]
extern crate quote;
extern crate proc_macro;
#[macro_use]
extern crate syn;
use proc_macro::TokenStream;
use quote::Tokens;
use syn::{DeriveInput, Meta, NestedMeta, Ident, Data, MetaList, DataEnum,
Fields, Path, LifetimeDef, GenericParam, Lifetime};
use syn::punctuated::Punctuated;
use std::collections::HashSet;
use std::iter::FromIterator;
#[proc_macro_derive(EnumKind, attributes(enum_kind))]
pub fn enum_kind(input: TokenStream) -> TokenStream {
let ast = syn::parse(input).expect("#[derive(EnumKind)] failed to parse input");
let (name, traits) = get_enum_specification(&ast);
let enum_ = create_kind_enum(&ast, &name, traits);
let impl_ = create_impl(&ast, &name);
let code = quote! {
#enum_
#impl_
};
code.into()
}
fn find_attribute(definition: &DeriveInput, name: &str)
-> Option<Punctuated<NestedMeta, syn::token::Comma>> {
for attr in definition.attrs.iter() {
match attr.interpret_meta() {
Some(Meta::List(MetaList { ident, ref nested, .. }))
if ident == name => return Some(nested.clone()),
_ => continue
}
}
None
}
fn get_enum_specification(definition: &DeriveInput) -> (Ident, Vec<Ident>) {
let params = find_attribute(definition, "enum_kind")
.expect("#[derive(EnumKind)] requires an associated enum_kind attribute to be specified");
let mut iter = params.iter();
if let Some(&NestedMeta::Meta(Meta::Word(ident))) = iter.next() {
let name = ident;
match iter.next() {
Some(&NestedMeta::Meta(Meta::List(MetaList { ident, ref nested, .. })))
if ident == "derive" => {
let mut to_derive = vec![];
for meta in nested.iter() {
if let &NestedMeta::Meta(Meta::Word(ident)) = meta {
to_derive.push(ident.clone());
} else {
panic!("#[enum_kind({}, derive(...))] attribute's derive specifier accepts only identifiers");
}
}
return (name, to_derive);
},
Some(_) => {
panic!("#[enum_kind({}, ...)] attribute has unknown extra specifiers", name);
}
None => {
return (name, vec![]);
}
}
} else {
panic!("#[enum_kind(NAME)] attribute requires NAME to be specified");
}
}
fn create_kind_enum(definition: &DeriveInput, kind_ident: &Ident, traits: Vec<Ident>) -> Tokens {
let variant_idents = match &definition.data {
&Data::Enum(DataEnum { ref variants, .. }) => {
variants.iter().map(|ref v| v.ident.clone())
}
_ => {
panic!("#[derive(EnumKind)] is only allowed for enums");
}
};
let visibility = &definition.vis;
let derives = Punctuated::<Ident, syn::token::Comma>::from_iter(traits);
quote! {
#[derive(Debug, Clone, Copy, PartialEq, Eq, #derives)]
#[allow(dead_code)]
#[allow(non_snake_case)]
#[allow(missing_docs)]
#visibility enum #kind_ident {
#(#variant_idents),*
}
}
}
fn is_uninhabited_enum(definition: &DeriveInput) -> bool {
if let Data::Enum(ref data) = definition.data {
return data.variants.len() == 0;
}
return false;
}
fn create_impl(definition: &DeriveInput, kind_ident: &Ident) -> Tokens {
let (_, ty_generics, where_clause) = definition.generics.split_for_impl();
let ident = &definition.ident;
let arms = match &definition.data {
&Data::Enum(DataEnum { ref variants, .. }) => {
variants.iter().map(|ref v| {
let variant = &v.ident;
match v.fields {
Fields::Unit => quote! {
&#ident::#variant => #kind_ident::#variant,
},
Fields::Unnamed(_) => quote! {
&#ident::#variant(..) => #kind_ident::#variant,
},
Fields::Named(_) => quote! {
&#ident::#variant{..} => #kind_ident::#variant,
}
}
})
}
_ => {
panic!("#[derive(EnumKind)] is only allowed for enums");
}
};
let trait_: Path = if cfg!(feature="no-stdlib") {
parse_quote!(::core::convert::From)
} else {
parse_quote!(::std::convert::From)
};
let mut counter: u32 = 1;
let used: HashSet<Lifetime> = definition.generics
.lifetimes()
.map(|ld| ld.lifetime.clone())
.collect();
let a = loop {
let lifetime: Lifetime = syn::parse_str(&format!("'__enum_kinds{}", counter))
.unwrap();
if !used.contains(&lifetime) {
break LifetimeDef::new(lifetime);
}
counter += 1;
};
let mut generics = definition.generics.clone();
generics.params.insert(0, GenericParam::Lifetime(a.clone()));
let (impl_generics, _, _) = generics.split_for_impl();
let impl_ = if is_uninhabited_enum(definition) {
quote! {
unreachable!();
}
} else {
quote!{
match _value {
#(#arms)*
}
}
};
quote! {
#[automatically_derived]
#[allow(unused_attributes)]
#[allow(missing_docs)]
impl #impl_generics #trait_<&#a #ident#ty_generics> for #kind_ident #where_clause {
fn from(_value: &#a #ident#ty_generics) -> Self {
#impl_
}
}
#[automatically_derived]
#[allow(unused_attributes)]
#[allow(missing_docs)]
impl #impl_generics #trait_<#ident#ty_generics> for #kind_ident #where_clause {
fn from(value: #ident#ty_generics) -> Self {
#kind_ident::from(&value)
}
}
}
}