pie-boot-macros 0.1.3

use proc_macro::TokenStream;
use proc_macro2::Span;
use quote::{format_ident, quote};
use syn::{ItemFn, Visibility, parse, parse_macro_input, spanned::Spanned};

pub fn entry(args: TokenStream, input: TokenStream, name: &str) -> TokenStream {
    let f = parse_macro_input!(input as ItemFn);

    // check the function arguments
    if f.sig.inputs.len() != 1 {
        return parse::Error::new(
            f.sig.inputs.last().unwrap().span(),
            "`#[entry]` function need one argument `&BootArgs`",
        )
        .to_compile_error()
        .into();
    }

    // check the function signature
    let valid_signature = f.sig.constness.is_none()
        && f.sig.asyncness.is_none()
        && f.vis == Visibility::Inherited
        && f.sig.abi.is_none()
        && f.sig.generics.params.is_empty()
        && f.sig.generics.where_clause.is_none()
        && f.sig.variadic.is_none()
        // && match f.sig.output {
        //     ReturnType::Default => false,
        //     ReturnType::Type(_, ref ty) => matches!(**ty, Type::Never(_)),
        // }
        ;

    if !valid_signature {
        return parse::Error::new(
            f.span(),
            "`#[entry]` function must have signature `[unsafe] fn([arg0: usize, ...]) `",
        )
        .to_compile_error()
        .into();
    }

    if !args.is_empty() {
        return parse::Error::new(Span::call_site(), "This attribute accepts no arguments")
            .to_compile_error()
            .into();
    }

    // XXX should we blacklist other attributes?
    let attrs = f.attrs;
    let unsafety = f.sig.unsafety;
    let args = f.sig.inputs;
    let stmts = f.block.stmts;
    let name = format_ident!("{}", name);

    quote!(
        #[allow(non_snake_case)]
        #[unsafe(no_mangle)]
        #(#attrs)*
        pub #unsafety extern "C" fn #name(#args) {
            #(#stmts)*
        }
    )
    .into()
}