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|
extern crate proc_macro;
// use dhall_syntax::*;
use proc_macro::TokenStream;
use quote::{quote, quote_spanned};
use syn::spanned::Spanned;
use syn::Error;
use syn::{parse_quote, DeriveInput};
pub fn derive_static_type(input: TokenStream) -> TokenStream {
TokenStream::from(match derive_static_type_inner(input) {
Ok(tokens) => tokens,
Err(err) => err.to_compile_error(),
})
}
fn static_type<T>(ty: T) -> proc_macro2::TokenStream
where
T: quote::ToTokens,
{
quote!(
<#ty as ::dhall::de::StaticType>::static_type()
)
}
fn derive_for_struct(
data: &syn::DataStruct,
constraints: &mut Vec<syn::Type>,
) -> Result<proc_macro2::TokenStream, Error> {
let fields = match &data.fields {
syn::Fields::Named(fields) => fields
.named
.iter()
.map(|f| {
let name = f.ident.as_ref().unwrap().to_string();
let ty = &f.ty;
(name, ty)
})
.collect(),
syn::Fields::Unnamed(fields) => fields
.unnamed
.iter()
.enumerate()
.map(|(i, f)| {
let name = format!("_{}", i + 1);
let ty = &f.ty;
(name, ty)
})
.collect(),
syn::Fields::Unit => vec![],
};
let entries = fields.into_iter().map(|(name, ty)| {
constraints.push(ty.clone());
let ty = static_type(ty);
quote!( (#name.to_owned(), #ty) )
});
Ok(quote! { ::dhall::de::Type::make_record_type(
vec![ #(#entries),* ].into_iter()
) })
}
fn derive_for_enum(
data: &syn::DataEnum,
constraints: &mut Vec<syn::Type>,
) -> Result<proc_macro2::TokenStream, Error> {
let entries: Vec<_> = data
.variants
.iter()
.map(|v| {
let name = v.ident.to_string();
match &v.fields {
syn::Fields::Unit => Ok(quote!( (#name.to_owned(), None) )),
syn::Fields::Unnamed(fields) if fields.unnamed.is_empty() => {
Ok(quote!( (#name.to_owned(), None) ))
}
syn::Fields::Unnamed(fields) if fields.unnamed.len() == 1 => {
let ty = &fields.unnamed.iter().next().unwrap().ty;
constraints.push(ty.clone());
let ty = static_type(ty);
Ok(quote!( (#name.to_owned(), Some(#ty)) ))
}
syn::Fields::Unnamed(_) => Err(Error::new(
v.span(),
"Variants with more than one field are not supported",
)),
syn::Fields::Named(_) => Err(Error::new(
v.span(),
"Named variants are not supported",
)),
}
})
.collect::<Result<_, Error>>()?;
Ok(quote! { ::dhall::de::Type::make_union_type(
vec![ #(#entries),* ].into_iter()
) })
}
pub fn derive_static_type_inner(
input: TokenStream,
) -> Result<proc_macro2::TokenStream, Error> {
let input: DeriveInput = syn::parse_macro_input::parse(input)?;
// List of types that must impl StaticType
let mut constraints = vec![];
let get_type = match &input.data {
syn::Data::Struct(data) => derive_for_struct(data, &mut constraints)?,
syn::Data::Enum(data) if data.variants.is_empty() => {
return Err(Error::new(
input.span(),
"Empty enums are not supported",
))
}
syn::Data::Enum(data) => derive_for_enum(data, &mut constraints)?,
syn::Data::Union(x) => {
return Err(Error::new(
x.union_token.span(),
"Unions are not supported",
))
}
};
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: StaticType, with an appropriate span
let assert_name =
syn::Ident::new(&format!("_AssertType{}", i), ty.span());
let mut local_where_clause = orig_where_clause.clone();
local_where_clause
.predicates
.push(parse_quote!(#ty: ::dhall::de::StaticType));
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 StaticType impl
let mut where_clause = orig_where_clause.clone();
for ty in constraints.iter() {
where_clause
.predicates
.push(parse_quote!(#ty: ::dhall::de::StaticType));
}
let ident = &input.ident;
let tokens = quote! {
impl #impl_generics ::dhall::de::StaticType
for #ident #ty_generics
#where_clause {
fn static_type() ->
::dhall::de::Type {
#(#assertions)*
#get_type
}
}
};
Ok(tokens)
}
|
