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|
//! Renderer Attribute Macro Implementation
//!
//! This module provides the `#[renderer]` attribute macro for automatically
//! generating structs that implement the `Renderer` trait from functions.
use proc_macro::TokenStream;
use quote::quote;
use syn::spanned::Spanned;
use syn::{FnArg, ItemFn, Pat, PatType, ReturnType, Signature, Type, TypePath, parse_macro_input};
/// Extracts the previous type and parameter name from function arguments
fn extract_previous_info(sig: &Signature) -> syn::Result<(Pat, TypePath)> {
// The function should have exactly one parameter
if sig.inputs.len() != 1 {
return Err(syn::Error::new(
sig.inputs.span(),
"Renderer function must have exactly one parameter (the previous type)",
));
}
// First and only parameter is the previous type
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
match &**ty {
Type::Path(type_path) => Ok((param_pat, type_path.clone())),
_ => Err(syn::Error::new(
ty.span(),
"Parameter type must be a type path",
)),
}
}
FnArg::Receiver(_) => Err(syn::Error::new(
arg.span(),
"Renderer function cannot have self parameter",
)),
}
}
/// Extracts the return type from the function signature
fn extract_return_type(sig: &Signature) -> syn::Result<()> {
// Renderer 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(),
"Renderer function must return () or have no return type",
)),
}
}
ReturnType::Default => Ok(()),
}
}
pub fn renderer_attr(item: TokenStream) -> TokenStream {
// 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(), "Renderer function cannot be async")
.to_compile_error()
.into();
}
// Extract the previous type and parameter name from function arguments
let (prev_param, previous_type) = match extract_previous_info(&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 renderer attribute)
let mut fn_attrs = input_fn.attrs.clone();
// Remove any #[renderer(...)] attributes to avoid infinite recursion
fn_attrs.retain(|attr| !attr.path().is_ident("renderer"));
// 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 = syn::Ident::new(&pascal_case_name, fn_name.span());
// Register the renderer in the global list
let renderer_entry = quote! {
#struct_name => #previous_type,
};
let renderer_exist_entry = quote! {
id if id == std::any::TypeId::of::<#previous_type>() => true,
};
let mut renderers = crate::RENDERERS.lock().unwrap();
let mut renderer_exist = crate::RENDERERS_EXIST.lock().unwrap();
let renderer_entry_str = renderer_entry.to_string();
let renderer_exist_entry_str = renderer_exist_entry.to_string();
if !renderers.contains(&renderer_entry_str) {
renderers.push(renderer_entry_str);
}
if !renderer_exist.contains(&renderer_exist_entry_str) {
renderer_exist.push(renderer_exist_entry_str);
}
// Generate the struct and implementation
// We need to create a wrapper function that adds the r parameter
let expanded = quote! {
#(#fn_attrs)*
#vis struct #struct_name;
impl ::mingling::Renderer for #struct_name {
type Previous = #previous_type;
fn render(#prev_param: Self::Previous, r: &mut ::mingling::RenderResult) {
// Create a local wrapper function that includes r parameter
// This allows r_println! to access r
#[allow(non_snake_case)]
fn render_wrapper(#prev_param: #previous_type, r: &mut ::mingling::RenderResult) {
#fn_body
}
// Call the wrapper function
render_wrapper(#prev_param, r);
}
}
// Keep the original function for internal use (without r parameter)
#(#fn_attrs)*
#vis fn #fn_name(#prev_param: #previous_type) {
let mut dummy_r = ::mingling::RenderResult::default();
let r = &mut dummy_r;
#fn_body
}
};
expanded.into()
}
|
