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|
//! Chain Attribute Macro Implementation
//!
//! This module provides the `#[chain]` attribute macro for automatically
//! generating structs that implement the `Chain` trait from async functions.
use proc_macro::TokenStream;
use quote::quote;
use syn::parse::{Parse, ParseStream};
use syn::spanned::Spanned;
use syn::{
FnArg, Ident, ItemFn, Pat, PatType, ReturnType, Signature, Type, TypePath, parse_macro_input,
};
/// Parses the chain attribute arguments
struct ChainAttribute {
struct_name: Ident,
}
impl Parse for ChainAttribute {
fn parse(input: ParseStream) -> syn::Result<Self> {
let struct_name = input.parse()?;
Ok(ChainAttribute { struct_name })
}
}
/// 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(),
"Chain 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
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(),
"Chain function cannot have self parameter",
)),
}
}
/// Extracts the return type from the function signature
fn extract_return_type(sig: &Signature) -> syn::Result<TypePath> {
match &sig.output {
ReturnType::Type(_, ty) => match &**ty {
Type::Path(type_path) => Ok(type_path.clone()),
_ => Err(syn::Error::new(
ty.span(),
"Return type must be a type path",
)),
},
ReturnType::Default => Err(syn::Error::new(
sig.span(),
"Chain function must have a return type",
)),
}
}
/// Implementation of the `#[chain]` attribute macro
///
/// This macro transforms an async function into a struct that implements
/// the `Chain` trait. The struct name is specified in the attribute.
///
/// # Examples
///
/// ```ignore
/// use mingling_macros::chain;
///
/// #[chain(InitEntry)]
/// pub async fn process(data: InitBegin) -> mingling::AnyOutput {
/// AnyOutput::new::<InitResult>("初始化成功！".to_string().into())
/// }
/// ```
///
/// This generates:
/// ```ignore
/// pub struct InitEntry;
/// impl Chain for InitEntry {
/// type Previous = InitBegin;
/// async fn proc(data: Self::Previous) -> mingling::AnyOutput {
/// AnyOutput::new::<InitResult>("初始化成功！".to_string().into())
/// }
/// }
/// ```
pub fn chain_attr(attr: TokenStream, item: TokenStream) -> TokenStream {
// Parse the attribute arguments
let chain_attr = parse_macro_input!(attr as ChainAttribute);
let struct_name = chain_attr.struct_name;
// Parse the function item
let input_fn = parse_macro_input!(item as ItemFn);
// Validate the function
if !input_fn.sig.asyncness.is_some() {
return syn::Error::new(input_fn.sig.span(), "Chain function must 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(),
};
// Extract the return type
let return_type = match extract_return_type(&input_fn.sig) {
Ok(ty) => ty,
Err(e) => return e.to_compile_error().into(),
};
// Get the function body
let fn_body = &input_fn.block;
// Get function attributes (excluding the chain attribute)
let mut fn_attrs = input_fn.attrs.clone();
// Remove any #[chain(...)] attributes to avoid infinite recursion
fn_attrs.retain(|attr| !attr.path().is_ident("chain"));
// Get function visibility
let vis = &input_fn.vis;
// Get function name
let fn_name = &input_fn.sig.ident;
// Generate the struct and implementation
let expanded = quote! {
#(#fn_attrs)*
#vis struct #struct_name;
impl ::mingling::Chain for #struct_name {
type Previous = #previous_type;
async fn proc(#prev_param: Self::Previous) -> #return_type {
// Call the original function
#fn_name(#prev_param).await
}
}
// Keep the original function for internal use
#(#fn_attrs)*
#vis async fn #fn_name(#prev_param: #previous_type) -> #return_type {
#fn_body
}
};
expanded.into()
}
|
