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use proc_macro::TokenStream;
use std::{fs::File, io::Write};
mod parse_fn;
/// Create an `entrypoint_expr` macro inside the guest program. This will be
/// used inside the ZKVM guest program to call the ZKVM guest wrapper's
/// `make_wrapper` macro with entrypoint function type.
///
/// The overarching goal is to call `make_wrapper` with an input, which
/// contains the function definition. This can only happen inside the guest,
/// since that is the only place where we have the definition (syntactically).
/// But you can only pass data to macros by "inlining" it as macro arguments
/// (i.e. macros work on syntax, so creating a variable wouldn't work). Also,
/// the `make_wrapper` definition doesn't exist in the guest, but the ZKVM
/// wrapper crate. For these reasons we create a macro which invokes
/// `make_wrapper` with the proper arguments.
///
/// # Usage
///
/// Inside your guest (under guests directory) add an attribute above your main
/// (entrypoint/start) function. It takes no arguments.
///
/// ```rust
/// #[guests_macro::proving_entrypoint]
/// fn main(...) -> ... { ..... }
/// ```
///
/// # Example output
///
/// ```rust
/// #[macro_export]
/// macro_rules! entrypoint_expr {
/// () => {
/// make_wrapper!{fn main(...) -> ...}
/// };
/// }
/// ```
#[proc_macro_attribute]
pub fn proving_entrypoint(_: TokenStream, mut item: TokenStream) -> TokenStream {
let (name, args, ret) = parse_fn::split_fn(&item);
// We also need to pass some type information to the host program compile-time.
// Put it in the file guests/type.txt.
let mut output = File::create("../type.txt").unwrap();
writeln!(output, "{}", &format!("{args}").replace('\n', " "));
write!(output, "{}", &format!("{ret}").replace('\n', " "));
item.extend(
format!(
"#[macro_export]
macro_rules! entrypoint_expr {{
() => {{
make_wrapper!{{{}{} -> {}}}
}};
}}",
name, args, ret
)
.parse::<TokenStream>(),
);
item
}
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