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extern crate proc_macro;
use proc_macro::TokenStream;
use quote::quote_spanned;
use syn::{spanned::Spanned, AttributeArgs, FnArg, ItemFn, Meta, NestedMeta};
fn is_http(args: &AttributeArgs) -> bool {
args.iter().any(|arg| match arg {
NestedMeta::Meta(Meta::Path(path)) => path.is_ident("http"),
_ => false,
})
}
#[proc_macro_attribute]
pub fn lambda(attr: TokenStream, item: TokenStream) -> TokenStream {
let input = syn::parse_macro_input!(item as ItemFn);
let args = syn::parse_macro_input!(attr as AttributeArgs);
let ret = &input.sig.output;
let name = &input.sig.ident;
let body = &input.block;
let attrs = &input.attrs;
let asyncness = &input.sig.asyncness;
let inputs = &input.sig.inputs;
if name != "main" {
let tokens = quote_spanned! { name.span() =>
compile_error!("only the main function can be tagged with #[lambda]");
};
return TokenStream::from(tokens);
}
if asyncness.is_none() {
let tokens = quote_spanned! { input.span() =>
compile_error!("the async keyword is missing from the function declaration");
};
return TokenStream::from(tokens);
}
let result = match inputs.len() {
2 => {
let event = match inputs.first().expect("expected event argument") {
FnArg::Typed(arg) => arg,
_ => {
let tokens = quote_spanned! { inputs.span() =>
compile_error!("fn main's first argument must be fully formed");
};
return TokenStream::from(tokens);
}
};
let event_name = &event.pat;
let event_type = &event.ty;
let context = match inputs.iter().nth(1).expect("expected context argument") {
FnArg::Typed(arg) => arg,
_ => {
let tokens = quote_spanned! { inputs.span() =>
compile_error!("fn main's second argument must be fully formed");
};
return TokenStream::from(tokens);
}
};
let context_name = &context.pat;
let context_type = &context.ty;
if is_http(&args) {
quote_spanned! { input.span() =>
#(#attrs)*
#asyncness fn main() {
async fn actual(#event_name: #event_type, #context_name: #context_type) #ret #body
let f = netlify_lambda_http::handler(actual);
netlify_lambda_http::lambda::run(f).await.unwrap();
}
}
} else {
quote_spanned! { input.span() =>
#(#attrs)*
#asyncness fn main() {
async fn actual(#event_name: #event_type, #context_name: #context_type) #ret #body
let f = netlify_lambda::handler_fn(actual);
netlify_lambda::run(f).await.unwrap();
}
}
}
}
_ => {
let tokens = quote_spanned! { inputs.span() =>
compile_error!("The #[lambda] macro can expects two arguments: a triggered event and lambda context.");
};
return TokenStream::from(tokens);
}
};
result.into()
}