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extern crate proc_macro;
// use dhall_core::*;
use proc_macro::TokenStream;
use quote::{quote, quote_spanned};
use syn::spanned::Spanned;
use syn::{parse_macro_input, parse_quote, DeriveInput};
pub fn derive_dhall_type(input: TokenStream) -> TokenStream {
let input = parse_macro_input!(input as DeriveInput);
// List of types that must impl DhallType
let mut constraints = vec![];
let dhall_type = match &input.data {
syn::Data::Struct(data) => match &data.fields {
syn::Fields::Named(fields) => {
let fields = fields.named.iter()
.map(|f| {
let name = f.ident.as_ref().unwrap().to_string();
let ty = &f.ty;
constraints.push(ty.clone());
quote!( m.insert(dhall_core::Label::from(#name), <#ty as dhall::DhallType>::dhall_type()); )
});
quote! { dhall_core::rc(dhall_core::Expr::RecordType({
use std::collections::BTreeMap;
let mut m = BTreeMap::new();
#(#fields)*
m
})) }
}
_ => quote!(dhall_generator::dhall_expr!(Bool)),
},
_ => quote!(dhall_generator::dhall_expr!(Bool)),
};
let mut generics = input.generics.clone();
generics.make_where_clause();
let (impl_generics, ty_generics, orig_where_clause) =
generics.split_for_impl();
let orig_where_clause = orig_where_clause.unwrap();
// Hygienic errors
let assertions = constraints.iter().enumerate().map(|(i, ty)| {
// Ensure that ty: DhallType, with an appropriate span
let assert_name =
syn::Ident::new(&format!("_AssertDhallType{}", i), ty.span());
let mut local_where_clause = orig_where_clause.clone();
local_where_clause
.predicates
.push(parse_quote!(#ty: dhall::DhallType));
let phantoms = generics.params.iter().map(|param| match param {
syn::GenericParam::Type(syn::TypeParam { ident, .. }) => {
quote!(#ident)
}
syn::GenericParam::Lifetime(syn::LifetimeDef {
lifetime, ..
}) => quote!(&#lifetime ()),
_ => unimplemented!(),
});
quote_spanned! {ty.span()=>
struct #assert_name #impl_generics #local_where_clause {
_phantom: std::marker::PhantomData<(#(#phantoms),*)>
};
}
});
// Ensure that all the fields have a DhallType impl
let mut where_clause = orig_where_clause.clone();
for ty in constraints.iter() {
where_clause
.predicates
.push(parse_quote!(#ty: dhall::DhallType));
}
let ident = &input.ident;
let tokens = quote! {
impl #impl_generics dhall::DhallType for #ident #ty_generics #where_clause {
fn dhall_type() -> dhall_core::DhallExpr {
#(#assertions)*
#dhall_type
}
}
};
TokenStream::from(tokens)
}
|
