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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::Error;
use syn::{parse_quote, DeriveInput};
pub fn derive_dhall_type(input: TokenStream) -> TokenStream {
TokenStream::from(match derive_dhall_type_inner(input) {
Ok(tokens) => tokens,
Err(err) => err.to_compile_error(),
})
}
pub 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 fields = fields.into_iter().map(|(name, ty)| {
constraints.push(ty.clone());
quote! {
m.insert(
dhall_core::Label::from(#name),
<#ty as dhall::DhallType>::dhall_type()
);
}
});
Ok(quote! { dhall_core::rc(dhall_core::Expr::RecordType({
use std::collections::BTreeMap;
let mut m = BTreeMap::new();
#(#fields)*
m
})) })
}
pub fn derive_for_enum(
data: &syn::DataEnum,
constraints: &mut Vec<syn::Type>,
) -> Result<proc_macro2::TokenStream, Error> {
let variants = data
.variants
.iter()
.map(|v| {
let name = v.ident.to_string();
let ty = match &v.fields {
syn::Fields::Unnamed(fields) if fields.unnamed.is_empty() => {
Err(Error::new(
v.span(),
"Nullary variants are not supported",
))
}
syn::Fields::Unnamed(fields) if fields.unnamed.len() > 1 => {
Err(Error::new(
v.span(),
"Variants with more than one field are not supported",
))
}
syn::Fields::Unnamed(fields) => {
Ok(&fields.unnamed.iter().next().unwrap().ty)
}
syn::Fields::Named(_) => Err(Error::new(
v.span(),
"Named variants are not supported",
)),
syn::Fields::Unit => Err(Error::new(
v.span(),
"Nullary variants are not supported",
)),
};
let ty = ty?;
constraints.push(ty.clone());
Ok(quote! {
m.insert(
dhall_core::Label::from(#name),
<#ty as dhall::DhallType>::dhall_type()
);
})
})
.collect::<Result<Vec<_>, Error>>()?;
Ok(quote! { dhall_core::rc(dhall_core::Expr::UnionType({
use std::collections::BTreeMap;
let mut m = BTreeMap::new();
#(#variants)*
m
})) })
}
pub fn derive_dhall_type_inner(
input: TokenStream,
) -> Result<proc_macro2::TokenStream, Error> {
let input: DeriveInput = syn::parse_macro_input::parse(input)?;
// List of types that must impl DhallType
let mut constraints = vec![];
let dhall_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: 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
}
}
};
Ok(tokens)
}
|
