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//! Setup Attribute Macro Implementation
//!
//! This module provides the `#[setup]` attribute macro for automatically
//! generating structs that implement the `ProgramSetup` trait from functions.
use proc_macro::TokenStream;
use quote::quote;
use syn::spanned::Spanned;
use syn::{FnArg, Ident, ItemFn, Pat, PatType, ReturnType, Signature, Type, parse_macro_input};
/// Extracts the program parameter from function arguments
fn extract_program_param(sig: &Signature) -> syn::Result<(Pat, Type)> {
// The function should have exactly one parameter
if sig.inputs.len() != 1 {
return Err(syn::Error::new(
sig.inputs.span(),
"Setup function must have exactly one parameter",
));
}
let arg = &sig.inputs[0];
match arg {
FnArg::Typed(PatType { pat, ty, .. }) => {
// Extract the pattern (parameter name)
let param_pat = (**pat).clone();
// Extract the type as-is
let param_type = (**ty).clone();
Ok((param_pat, param_type))
}
FnArg::Receiver(_) => Err(syn::Error::new(
arg.span(),
"Setup function cannot have self parameter",
)),
}
}
/// Extracts and validates the return type
fn extract_return_type(sig: &Signature) -> syn::Result<()> {
// Setup functions should return () or have no return type
match &sig.output {
ReturnType::Type(_, ty) => {
// Check if it's ()
match &**ty {
Type::Tuple(tuple) if tuple.elems.is_empty() => Ok(()),
_ => Err(syn::Error::new(
ty.span(),
"Setup function must return () or have no return type",
)),
}
}
ReturnType::Default => Ok(()),
}
}
pub fn setup_attr(attr: TokenStream, item: TokenStream) -> TokenStream {
// Parse the attribute arguments (e.g., MyProgram from #[setup(MyProgram)])
// If no argument is provided, use ThisProgram
let (program_name, use_crate_prefix) = if attr.is_empty() {
(
Ident::new("ThisProgram", proc_macro2::Span::call_site()),
true,
)
} else {
(parse_macro_input!(attr as Ident), false)
};
// Parse the function item
let input_fn = parse_macro_input!(item as ItemFn);
// Validate the function is not async
if input_fn.sig.asyncness.is_some() {
return syn::Error::new(input_fn.sig.span(), "Setup function cannot be async")
.to_compile_error()
.into();
}
// Extract the program parameter
let (program_param, program_type) = match extract_program_param(&input_fn.sig) {
Ok(info) => info,
Err(e) => return e.to_compile_error().into(),
};
// Validate return type
if let Err(e) = extract_return_type(&input_fn.sig) {
return e.to_compile_error().into();
}
// Get the function body
let fn_body = &input_fn.block;
// Get function attributes (excluding the setup attribute)
let mut fn_attrs = input_fn.attrs.clone();
// Remove any #[setup(...)] attributes to avoid infinite recursion
fn_attrs.retain(|attr| !attr.path().is_ident("setup"));
// Get function visibility
let vis = &input_fn.vis;
// Get function name
let fn_name = &input_fn.sig.ident;
// Generate struct name from function name using pascal_case
let pascal_case_name = just_fmt::pascal_case!(fn_name.to_string());
let struct_name = Ident::new(&pascal_case_name, fn_name.span());
// Generate the struct and implementation
let expanded = if use_crate_prefix {
quote! {
#(#fn_attrs)*
#[doc(hidden)]
#vis struct #struct_name;
impl ::mingling::setup::ProgramSetup<ThisProgram, ThisProgram> for #struct_name {
fn setup(&mut self, program: &mut ::mingling::Program<ThisProgram, ThisProgram>) {
// Call the original function with the actual Program type
#fn_name(program);
}
}
// Keep the original function for internal use
#(#fn_attrs)*
#vis fn #fn_name(#program_param: #program_type) {
#fn_body
}
}
} else {
quote! {
#(#fn_attrs)*
#vis struct #struct_name;
impl ::mingling::setup::ProgramSetup<#program_name, #program_name> for #struct_name {
fn setup(&mut self, program: &mut ::mingling::Program<#program_name, #program_name>) {
// Call the original function with the actual Program type
#fn_name(program);
}
}
// Keep the original function for internal use
#(#fn_attrs)*
#vis fn #fn_name(#program_param: #program_type) {
#fn_body
}
}
};
expanded.into()
}