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extern crate proc_macro;
use proc_macro::TokenStream;
use quote::{quote, ToTokens};
use std::borrow::Cow;
use syn::ext::IdentExt;
use syn::parse::{Nothing, Parse, ParseStream};
use syn::spanned::Spanned;
use syn::{
parse_macro_input, Attribute, FnArg, Generics, Ident, ImplItem, ImplItemConst, ImplItemFn,
ImplItemType, ItemImpl, Pat, PatIdent, PatReference, PatTuple, PatType, Receiver, Signature,
Visibility,
};
struct ItemImplWithVisibility {
attrs: Vec<Attribute>,
visibility: Visibility,
impl_item: ItemImpl,
}
impl Parse for ItemImplWithVisibility {
fn parse(input: ParseStream) -> syn::Result<Self> {
let attrs = input.call(Attribute::parse_outer)?;
let visibility = input.parse()?;
let impl_item = input.parse()?;
Ok(Self {
attrs,
visibility,
impl_item,
})
}
}
#[proc_macro_attribute]
pub fn extension_trait(args: TokenStream, input: TokenStream) -> TokenStream {
parse_macro_input!(args as Nothing);
let ItemImplWithVisibility {
attrs,
visibility,
impl_item,
} = parse_macro_input!(input as ItemImplWithVisibility);
let ItemImpl {
impl_token,
unsafety,
trait_,
items,
..
} = &impl_item;
let items = items.iter().map(|item| match item {
ImplItem::Const(ImplItemConst {
attrs,
vis: _,
defaultness: None,
const_token,
ident,
generics: Generics {
lt_token: None,
params: _,
gt_token: None,
where_clause: None,
},
colon_token,
ty,
eq_token: _,
expr: _,
semi_token,
}) => quote! { #(#attrs)* #const_token #ident #colon_token #ty #semi_token },
ImplItem::Fn(ImplItemFn {
attrs,
vis: _,
defaultness: None,
sig: Signature {
constness,
asyncness,
unsafety,
abi,
fn_token,
ident,
generics,
paren_token: _,
inputs,
variadic,
output
},
block: _,
}) => {
let inputs = inputs.into_iter().map(|arg| {
let span = arg.span();
match arg {
FnArg::Typed(PatType { attrs, pat, colon_token, ty }) => {
let ident = extract_ident(pat).unwrap_or_else(|| Cow::Owned(Ident::new("_", span)));
quote! { #(#attrs)* #ident #colon_token #ty }
},
FnArg::Receiver(Receiver {
attrs,
reference: None,
mutability: _,
self_token,
colon_token: Some(colon),
ty,
}) => quote! { #(#attrs)* #self_token #colon #ty },
FnArg::Receiver(receiver) => receiver.into_token_stream(),
}
});
let where_clause = &generics.where_clause;
quote! {
#(#attrs)*
#constness #asyncness #unsafety #abi #fn_token #ident #generics (#(#inputs,)* #variadic) #output #where_clause;
}
},
ImplItem::Type(ImplItemType {
attrs,
type_token,
ident,
generics,
semi_token,
..
}) => quote! { #(#attrs)* #type_token #ident #generics #semi_token },
_ => syn::Error::new(item.span(), "unsupported item type").to_compile_error(),
});
if let Some((None, path, _)) = trait_ {
(quote! {
#(#attrs)*
#visibility #unsafety trait #path {
#(#items)*
}
#impl_item
})
.into()
} else {
syn::Error::new(impl_token.span(), "extension trait name was not provided")
.to_compile_error()
.into()
}
}
fn extract_ident(pat: &Pat) -> Option<Cow<'_, Ident>> {
match pat {
Pat::Reference(PatReference { pat, .. }) => extract_ident(pat),
Pat::Ident(PatIdent { ident, .. }) => Some(Cow::Borrowed(ident)),
Pat::Tuple(PatTuple { elems, .. }) => {
if elems.len() <= 1 {
extract_ident(elems.into_iter().next()?)
} else {
let span = elems.span();
let elems = elems
.into_iter()
.map(extract_ident)
.map(|o| o.map(|ident| ident.unraw().to_string()))
.collect::<Option<Vec<String>>>()?;
let joined = elems.join("_");
Some(Cow::Owned(Ident::new(&joined, span)))
}
}
_ => None,
}
}