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use crate::generics::{
clause_to_toks, impl_generics, GenericParam, Generics, TypeParamBound, WherePredicate,
};
use proc_macro2::{Span, TokenStream};
use proc_macro_error::emit_error;
use quote::{quote, ToTokens, TokenStreamExt};
use syn::punctuated::Punctuated;
use syn::token::Comma;
use syn::{parse2, FnArg, Ident, Item, Path, PathArguments, Token, TraitItem, Type, TypePath};
pub struct ForDeref {
generics: Generics,
definitive: Ident,
targets: Punctuated<Type, Comma>,
}
mod parsing {
use super::*;
use syn::parse::{Error, Parse, ParseStream, Result};
impl Parse for ForDeref {
fn parse(input: ParseStream) -> Result<Self> {
let _ = input.parse::<Token![for]>()?;
let mut generics: Generics = input.parse()?;
let targets = Punctuated::parse_separated_nonempty(input)?;
let mut lookahead = input.lookahead1();
if lookahead.peek(Token![where]) {
generics.where_clause = Some(input.parse()?);
lookahead = input.lookahead1();
}
if !input.is_empty() {
return Err(lookahead.error());
}
let mut definitive: Option<Ident> = None;
for param in &generics.params {
if let GenericParam::Type(param) = param {
for bound in ¶m.bounds {
if matches!(bound, TypeParamBound::TraitSubst(_)) {
definitive = Some(param.ident.clone());
break;
}
}
}
}
if definitive.is_none() {
if let Some(clause) = generics.where_clause.as_ref() {
for pred in &clause.predicates {
if let WherePredicate::Type(pred) = pred {
for bound in &pred.bounds {
if matches!(bound, TypeParamBound::TraitSubst(_)) {
match pred.bounded_ty {
Type::Path(TypePath {
qself: None,
path:
Path {
leading_colon: None,
ref segments,
},
}) if segments.len() == 1
&& matches!(
segments[0].arguments,
PathArguments::None
) =>
{
definitive = Some(segments[0].ident.clone());
break;
}
_ => (),
}
}
}
}
}
}
}
let definitive = match definitive {
Some(def) => def,
None => {
return Err(Error::new(
Span::call_site(),
"no definitive type parameter: require a parameter bound like `T: trait``",
));
}
};
Ok(ForDeref {
generics,
definitive,
targets,
})
}
}
}
impl ForDeref {
pub fn expand(self, item: TokenStream) -> TokenStream {
let item = match parse2::<Item>(item) {
Ok(Item::Trait(item)) => item,
Ok(item) => {
emit_error!(item, "expected trait");
return TokenStream::new();
}
Err(err) => {
emit_error!(err);
return TokenStream::new();
}
};
let trait_ident = &item.ident;
let (_, ty_generics, _) = item.generics.split_for_impl();
let trait_ty = quote! { #trait_ident #ty_generics };
let impl_generics = impl_generics(&self.generics, &trait_ty);
let where_clause = clause_to_toks(
&self.generics.where_clause,
item.generics.where_clause.as_ref(),
&trait_ty,
);
let definitive = self.definitive;
let definitive = quote! { < #definitive as #trait_ty > };
let mut toks = TokenStream::new();
for target in self.targets {
let mut impl_items = TokenStream::new();
for item in &item.items {
match item {
TraitItem::Const(item) => {
let ident = &item.ident;
let ty = &item.ty;
impl_items.append_all(quote! {
const #ident : #ty = #definitive :: #ident;
});
}
TraitItem::Method(item) => {
let sig = &item.sig;
let ident = &sig.ident;
let params = sig.inputs.iter().map(|arg| match arg {
FnArg::Receiver(arg) => &arg.self_token as &dyn ToTokens,
FnArg::Typed(arg) => &arg.pat,
});
impl_items.append_all(quote! {
#sig {
#definitive :: #ident ( #(#params),* )
}
});
}
TraitItem::Type(item) => {
let ident = &item.ident;
impl_items.append_all(quote! {
type #ident = #definitive :: #ident;
});
}
TraitItem::Macro(item) => {
emit_error!(item, "unsupported: macro item in trait");
}
TraitItem::Verbatim(item) => {
emit_error!(item, "unsupported: verbatim item in trait");
}
_ => (),
}
}
toks.append_all(quote! {
impl #impl_generics #trait_ty for #target #where_clause {
#impl_items
}
});
}
toks
}
}
