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extern crate proc_macro;
use proc_macro2::{Delimiter, Span, TokenStream, TokenTree};
use proc_macro_error::{abort, abort_call_site, proc_macro_error};
use quote::quote;
use syn::{parse_macro_input, AttrStyle, Attribute, Data, DeriveInput, Expr, Ident};
#[proc_macro_derive(TryFrom)]
#[proc_macro_error]
pub fn derive_try_from(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
let input = parse_macro_input!(input as DeriveInput);
let reprtype = find_repr_type(input.attrs);
let enum_name = input.ident;
let enum_data = get_enum_data(&input.data);
let match_expr = match_impl(&enum_name, enum_data);
proc_macro::TokenStream::from(quote! {
impl core::convert::TryFrom<#reprtype> for #enum_name {
type Error = #reprtype;
fn try_from(val : #reprtype) -> Result<Self, <Self as core::convert::TryFrom<#reprtype>>::Error> {
#match_expr
}
}
})
}
#[proc_macro_derive(Into)]
#[proc_macro_error]
pub fn derive_into(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
let input = parse_macro_input!(input as DeriveInput);
let reprtype = find_repr_type(input.attrs);
let enum_name = input.ident;
proc_macro::TokenStream::from(quote! {
impl core::convert::Into<#reprtype> for #enum_name {
fn into(self : #enum_name) -> #reprtype {
self as #reprtype
}
}
})
}
fn find_repr_type(attrs: Vec<Attribute>) -> Ident {
for attr in attrs {
match attr.style {
AttrStyle::Outer => {
if attr.path.is_ident(&Ident::new("repr", Span::call_site())) {
let tokens = attr.tokens;
let mut repr_tokens_iter = tokens.into_iter();
let first_token: TokenTree = repr_tokens_iter.next().unwrap();
if repr_tokens_iter.next().is_some() {
abort!(
first_token.span(),
"Repr is malformed, expecting repr(TYPE)"
);
}
let repr_type = match first_token.clone() {
TokenTree::Group(repr_items) => {
if repr_items.delimiter() != Delimiter::Parenthesis {
abort!(repr_items.span(), "Repr is malformed, expecting repr(TYPE)")
}
let mut repr_types_iter = repr_items.stream().into_iter();
let first_repr_item = repr_types_iter.next().unwrap();
if let Some(second_repr_type) = repr_types_iter.next() {
abort!(
second_repr_type.span(),
"Many repr types specified. Expecting only one."
)
}
match first_repr_item.clone() {
TokenTree::Ident(repr_type) => repr_type,
unexpected_type => abort!(
first_repr_item.span(),
"Unexpected type in repr {}",
unexpected_type
),
}
}
unexpected_token => abort!(
first_token.span(),
"Unexpected token with repr {}",
unexpected_token
),
};
return repr_type;
}
}
_ => {
continue;
}
}
}
abort_call_site!("Repr not found");
}
fn get_enum_data(data: &Data) -> Vec<(Ident, Expr)> {
let mut enum_data: Vec<(Ident, Expr)> = Vec::new();
match *data {
Data::Enum(ref data) => {
for variant in data.variants.iter() {
let pair = variant.discriminant.as_ref().unwrap();
let expr = pair.1.clone();
enum_data.push((variant.ident.clone(), expr));
}
}
Data::Struct(_) | Data::Union(_) => {
abort_call_site!("Unexpected type! Use derive with enums only")
}
}
enum_data
}
fn match_impl(enum_name: &Ident, enum_data: Vec<(Ident, Expr)>) -> TokenStream {
let mut match_arms = TokenStream::new();
for (id, expr) in enum_data {
match_arms.extend(quote! { #expr => Ok(#enum_name::#id),});
}
match_arms.extend(quote! { unexpected => Err(unexpected) });
quote! {
match val {
#match_arms
}
}
}