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use proc_macro::TokenStream;
use quote::{format_ident, quote, ToTokens};
use syn::{parse_macro_input, Error, FnArg, ImplItem, ItemImpl, Pat, ReturnType, Type, Visibility};
const SCALAR_TYPES: &[&str] = &[
"bool", // Boolean type
"char", // Character type
"i8", // 8-bit signed integer
"i16", // 16-bit signed integer
"i32", // 32-bit signed integer
"i64", // 64-bit signed integer
"i128", // 128-bit signed integer
"isize", // Pointer-sized signed integer
"u8", // 8-bit unsigned integer
"u16", // 16-bit unsigned integer
"u32", // 32-bit unsigned integer
"u64", // 64-bit unsigned integer
"u128", // 128-bit unsigned integer
"usize", // Pointer-sized unsigned integer
"f32", // 32-bit floating point
"f64", // 64-bit floating point
];
fn modify_type_to_pointer(ty: &Type) -> proc_macro2::TokenStream {
match ty {
Type::Reference(type_reference) => {
let elem = &type_reference.elem;
if let Type::Slice(type_slice) = &**elem {
let inner = &type_slice.elem;
if type_reference.mutability.is_some() {
quote! { *mut #inner }
} else {
quote! { *const #inner }
}
} else if type_reference.mutability.is_some() {
quote! { *mut #elem }
} else {
quote! { *const #elem }
}
}
Type::Ptr(ptr) => quote! { #ptr },
Type::Path(type_path) => {
if let Some(segment) = type_path.path.segments.last() {
if SCALAR_TYPES.contains(&segment.ident.to_string().as_str()) {
return quote! { #ty };
}
}
quote! { *mut #ty }
}
_ => quote! { *mut #ty },
}
}
#[proc_macro_attribute]
pub fn c_compatible(_attr: TokenStream, item: TokenStream) -> TokenStream {
let input = parse_macro_input!(item as ItemImpl);
let struct_name = &input.self_ty;
let mut has_create = false;
let mut has_destroy = false;
let trait_name = input
.trait_
.as_ref()
.map(|(_, path, _)| path.segments.last().unwrap().ident.to_string());
let mut c_compatible_fns = vec![];
let mut errors = vec![];
for item in &input.items {
if let ImplItem::Fn(method) = item {
if trait_name.is_none() && !matches!(method.vis, Visibility::Public(_)) {
continue;
}
let fn_name = &method.sig.ident;
let mut is_create = false;
let mut is_destroy = false;
if fn_name == "create" {
is_create = true;
has_create = true;
} else if fn_name == "destroy" {
is_destroy = true;
has_destroy = true;
}
let c_fn_name = if let Some(trait_name) = &trait_name {
format_ident!(
"{}_{}_{}",
struct_name.to_token_stream().to_string().to_lowercase(),
trait_name.to_lowercase(),
fn_name
)
} else {
format_ident!(
"{}_{}",
struct_name.to_token_stream().to_string().to_lowercase(),
fn_name
)
};
let mut params = vec![];
let mut args = vec![];
let return_type = &method.sig.output;
let mut self_param = None;
for (i, arg) in method.sig.inputs.iter().enumerate() {
match arg {
FnArg::Receiver(receiver) => {
if i != 0 {
let error = Error::new_spanned(
receiver,
"Self parameter must be the first parameter",
);
errors.push(error);
continue;
}
self_param = Some(receiver);
}
FnArg::Typed(pat_type) => {
if let Pat::Ident(pat_ident) = &*pat_type.pat {
let ident = &pat_ident.ident;
let ty = &*pat_type.ty;
let modified_ty = modify_type_to_pointer(ty);
if let Type::Reference(type_reference) = ty {
if let Type::Slice(_) = &*type_reference.elem {
let ptr_ident = format_ident!("{}_ptr", ident);
let len_ident = format_ident!("{}_len", ident);
params.push(
quote! { #ptr_ident: #modified_ty, #len_ident: usize },
);
args.push(quote! { #ident });
continue;
}
}
params.push(quote! { #ident: #modified_ty });
args.push(quote! { #ident });
}
}
}
}
let (ptr_type, self_expr, is_consuming) = if let Some(receiver) = self_param {
if is_create {
errors.push(Error::new_spanned(
receiver,
"Create function cannot receive self as argument",
));
}
if receiver.reference.is_none() {
(
quote! { *mut },
quote! { unsafe { Box::from_raw(ptr) } },
true,
)
} else if receiver.mutability.is_some() {
if is_destroy {
errors.push(Error::new_spanned(
receiver,
"Destroy function must receive owned self argument. &mut self found instead"
));
}
(quote! { *mut }, quote! { unsafe { &mut *ptr } }, false)
} else {
if is_destroy {
errors.push(Error::new_spanned(
self_param,
"Destroy function must receive owned self argument. &self found instead"
));
}
(quote! { *const }, quote! { unsafe { &*ptr } }, false)
}
} else {
if is_destroy {
errors.push(Error::new_spanned(
self_param,
"Destroy function must receive owned self argument. Found no receiver",
));
}
(quote! {}, quote! {}, false)
};
let fn_call = if self_param.is_some() {
let args_converted = args.iter().zip(method.sig.inputs.iter().skip(1)).map(|(arg, input)| {
if let FnArg::Typed(pat_type) = input {
let ty = &*pat_type.ty;
match ty {
Type::Reference(type_reference) => {
if let Type::Slice(_) = &*type_reference.elem {
let arg_str = arg.to_string();
let ptr_ident = format_ident!("{}_ptr", arg_str);
let len_ident = format_ident!("{}_len", arg_str);
if type_reference.mutability.is_some() {
quote! { unsafe { core::slice::from_raw_parts_mut(#ptr_ident, #len_ident) } }
} else {
quote! { unsafe { core::slice::from_raw_parts(#ptr_ident, #len_ident) } }
}
} else if type_reference.mutability.is_some() {
quote! { unsafe { &mut *#arg } }
} else {
quote! { unsafe { &*#arg } }
}
}
Type::Ptr(_) => quote! { #arg },
Type::Path(type_path) => {
if let Some(segment) = type_path.path.segments.last() {
if type_path.path.leading_colon.is_none() && segment.arguments.is_empty() && !SCALAR_TYPES.contains(&segment.ident.to_string().as_str()) {
errors.push(
Error::new_spanned(
type_path,
"Only scalar types can be passed directly to functions without being behind refs or pointers"
)
);
}
};
quote! { #arg }
}
_ => {
errors.push(
Error::new_spanned(
arg,
"Only scalar types can be passed directly to functions without being behind refs or pointers"
)
);
quote! { #arg }
},
}
} else {
quote! { #arg }
}
});
if is_consuming {
quote! { #self_expr.#fn_name(#(#args_converted),*) }
} else {
quote! { (#self_expr).#fn_name(#(#args_converted),*) }
}
} else {
let args_converted = args.iter().zip(method.sig.inputs.iter()).map(|(arg, input)| {
if let FnArg::Typed(pat_type) = input {
let ty = &*pat_type.ty;
match ty {
Type::Reference(type_reference) => {
if let Type::Slice(_) = &*type_reference.elem {
let arg_str = arg.to_string();
let ptr_ident = format_ident!("{}_ptr", arg_str);
let len_ident = format_ident!("{}_len", arg_str);
if type_reference.mutability.is_some() {
quote! { unsafe { core::slice::from_raw_parts_mut(#ptr_ident, #len_ident) } }
} else {
quote! { unsafe { core::slice::from_raw_parts(#ptr_ident, #len_ident) } }
}
} else if type_reference.mutability.is_some() {
quote! { unsafe { &mut *#arg } }
} else {
quote! { unsafe { &*#arg } }
}
}
Type::Path(type_path) => {
if let Some(segment) = type_path.path.segments.last() {
if type_path.path.leading_colon.is_none() && segment.arguments.is_empty() && !SCALAR_TYPES.contains(&segment.ident.to_string().as_str()) {
errors.push(
Error::new_spanned(
type_path,
"Only scalar types can be passed directly to functions without being behind refs or pointers"
)
);
}
};
quote! { #arg }
}
_ => {
errors.push(
Error::new_spanned(
arg,
"Only scalar types can be passed directly to functions without being behind refs or pointers"
)
);
quote! { #arg }
},
}
} else {
quote! { #arg }
}
});
quote! { #struct_name::#fn_name(#(#args_converted),*) }
};
// Handle Self return type
let (modified_return_type, return_expr) = match return_type {
ReturnType::Type(_, ty) => {
if let Type::Path(type_path) = &**ty {
if let Some(segment) = type_path.path.segments.last() {
if !SCALAR_TYPES.contains(&segment.ident.to_string().as_str()) {
let owned_return_type = &segment.ident;
if owned_return_type == "Self" {
(
quote! { -> *mut #struct_name },
quote! { Box::into_raw(Box::new(#fn_call)) },
)
} else {
(
quote! { -> *mut #type_path },
quote! { Box::into_raw(Box::new(#fn_call)) },
)
}
} else {
(quote! { #return_type }, quote! { #fn_call })
}
} else {
(quote! { #type_path }, quote! { #fn_call })
}
} else if let Type::Reference(refr) = &**ty {
let inner_type = &*refr.elem;
if refr.mutability.is_some() {
(
quote! { -> *mut #inner_type },
quote! { #fn_call as *mut #inner_type },
)
} else {
(
quote! { -> *const #inner_type },
quote! { #fn_call as *const #inner_type },
)
}
} else {
(quote! { #return_type }, quote! { #fn_call })
}
}
_ => (quote! { #return_type }, quote! { #fn_call }),
};
// Preserve doc comments
let doc_comments = method
.attrs
.iter()
.filter(|attr| attr.path().is_ident("doc"))
.collect::<Vec<_>>();
let wrapper_fn = if self_param.is_some() {
quote! {
#(#doc_comments)*
#[no_mangle]
pub extern "C" fn #c_fn_name(ptr: #ptr_type #struct_name, #(#params),*) #modified_return_type {
// SAFETY: This function is unsafe because it works with raw pointers.
// The caller must ensure that all pointers are valid and properly aligned.
#return_expr
}
}
} else {
quote! {
#(#doc_comments)*
#[no_mangle]
pub unsafe extern "C" fn #c_fn_name(#(#params),*) #modified_return_type {
// SAFETY: This function is unsafe because it works with raw pointers.
// The caller must ensure that all pointers are valid and properly aligned.
#return_expr
}
}
};
c_compatible_fns.push(wrapper_fn);
}
}
if trait_name.is_none() && (!has_create || !has_destroy) {
let missing = if !has_create { "create" } else { "destroy" };
errors.push(Error::new_spanned(
&input,
format!(
"Struct must have both 'create' and 'destroy' functions. Missing: {}",
missing
),
));
}
if !errors.is_empty() {
let compile_errors = errors.iter().map(Error::to_compile_error);
return quote! {
#(#compile_errors)*
}
.into();
}
let expanded = quote! {
#input
#(#c_compatible_fns)*
};
expanded.into()
}