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|
extern crate proc_macro;
use proc_macro::TokenStream;
use proc_macro2::Span;
use quote::{quote_spanned, ToTokens};
use syn::parse::Parse;
use syn::spanned::Spanned;
use syn::{parse_macro_input, parse_quote, FnArg, Ident, Item, ItemMod, LitStr, PatType};
struct BuiltinArgs {
name: LitStr,
}
impl Parse for BuiltinArgs {
fn parse(input: syn::parse::ParseStream) -> syn::Result<Self> {
Ok(BuiltinArgs {
name: input.parse()?,
})
}
}
/// Mark the annotated module as a module for defining Nix builtins.
///
/// A function `fn builtins() -> Vec<Builtin>` will be defined within the annotated module,
/// returning a list of [`tvix_eval::Builtin`] for each function annotated with the `#[builtin]`
/// attribute within the module.
///
/// Each invocation of the `#[builtin]` annotation within the module should be passed a string
/// literal for the name of the builtin.
///
/// # Examples
/// ```ignore
/// # use tvix_eval_builtin_macros::builtins;
/// # mod value {
/// # pub use tvix_eval::Builtin;
/// # }
///
/// #[builtins]
/// mod builtins {
/// use tvix_eval::{ErrorKind, Value, VM};
///
/// #[builtin("identity")]
/// pub fn builtin_identity(_vm: &mut VM, x: Value) -> Result<Value, ErrorKind> {
/// Ok(x)
/// }
///
/// // Builtins can request their argument not be forced before being called by annotating the
/// // argument with the `#[lazy]` attribute
///
/// #[builtin("tryEval")]
/// pub fn builtin_try_eval(vm: &mut VM, #[lazy] x: Value) -> Result<Value, ErrorKind> {
/// todo!()
/// }
/// }
/// ```
#[proc_macro_attribute]
pub fn builtins(_args: TokenStream, item: TokenStream) -> TokenStream {
let mut module = parse_macro_input!(item as ItemMod);
let (_, items) = match &mut module.content {
Some(content) => content,
None => {
return (quote_spanned!(module.span() =>
compile_error!("Builtin modules must be defined in-line")
))
.into();
}
};
let mut builtins = vec![];
for item in items.iter_mut() {
if let Item::Fn(f) = item {
if let Some(builtin_attr_pos) = f
.attrs
.iter()
.position(|attr| attr.path.get_ident().iter().any(|id| *id == "builtin"))
{
let builtin_attr = f.attrs.remove(builtin_attr_pos);
let BuiltinArgs { name } = match builtin_attr.parse_args() {
Ok(args) => args,
Err(err) => return err.into_compile_error().into(),
};
if f.sig.inputs.len() <= 1 {
return (quote_spanned!(
f.sig.inputs.span() =>
compile_error!("Builtin functions must take at least two arguments")
))
.into();
}
let strictness = f
.sig
.inputs
.iter_mut()
.skip(1)
.map(|input| {
let mut lazy = false;
if let FnArg::Typed(PatType { attrs, .. }) = input {
attrs.retain(|attr| {
attr.path.get_ident().into_iter().any(|id| {
if id == "lazy" {
lazy = true;
false
} else {
true
}
})
});
}
!lazy
})
.collect::<Vec<_>>();
let fn_name = f.sig.ident.clone();
let args = (0..(f.sig.inputs.len() - 1))
.map(|n| Ident::new(&format!("arg_{n}"), Span::call_site()))
.collect::<Vec<_>>();
let mut reversed_args = args.clone();
reversed_args.reverse();
builtins.push(quote_spanned! { builtin_attr.span() => {
crate::internal::Builtin::new(
#name,
&[#(#strictness),*],
|mut args: Vec<crate::Value>, vm: &mut crate::internal::VM| {
#(let #reversed_args = args.pop().unwrap();)*
#fn_name(vm, #(#args),*)
}
)
}});
}
}
}
items.push(parse_quote! {
pub fn builtins() -> Vec<crate::internal::Builtin> {
vec![#(#builtins),*]
}
});
module.into_token_stream().into()
}
|
