1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161
extern crate proc_macro; use proc_macro::TokenStream; use proc_macro2::TokenStream as TokenStream2; use quote::{format_ident, quote, quote_spanned, ToTokens}; use syn::{ parse_macro_input, spanned::Spanned, FnArg, Ident, ImplGenerics, ImplItem, ImplItemMethod, ItemImpl, ReturnType, Signature, Type, TypeGenerics, WhereClause, }; type Generics<'a> = (ImplGenerics<'a>, TypeGenerics<'a>, Option<&'a WhereClause>); #[proc_macro_attribute] pub fn functionate(_args: TokenStream, item: TokenStream) -> TokenStream { let item = parse_macro_input!(item as ItemImpl); TokenStream::from(functionate_impl(item)) } fn functionate_impl(item: ItemImpl) -> TokenStream2 { let ItemImpl { generics, trait_: tr, self_ty: ty, items, .. } = &item; let ty = match ty.as_ref() { Type::Path(ty) => ty.path.get_ident().unwrap(), _ => panic!("Bad type"), }; let generics = generics.split_for_impl(); if let Some(_) = tr { return quote_spanned! { item.span() => compile_error!("expected bare impl"); }; } let impls = items .iter() .filter_map(|item| match item { ImplItem::Method(method) => Some(method), _ => None, }) .map(|method| method_to_impl(ty, &generics, method)); quote! { #(#impls)* } } enum SelfTy { Owned, MutRef, Ref, } fn method_to_impl(ty: &Ident, generics: &Generics, method: &ImplItemMethod) -> TokenStream2 { let (impl_generics, ty_generics, where_clause) = generics; let recv = method.sig.receiver(); let recv = match recv { Some(FnArg::Receiver(s)) => match &s.reference { Some(_) => match &s.mutability { Some(_) => SelfTy::MutRef, None => SelfTy::Ref, }, None => SelfTy::Owned, }, _ => { return quote_spanned! { method.sig.span() => "expected a method (custom self types are not supported)" } } }; let Signature { ident, inputs, output, .. } = &method.sig; let block = &method.block; let tr_ident = format_ident!("_{}Functionate_{}", ty, ident); let output = match output { ReturnType::Default => quote! { () }, ReturnType::Type(_, ty) => ty.into_token_stream(), }; let arg_names = inputs .iter() .filter_map(|arg| match arg { FnArg::Receiver(_) => None, FnArg::Typed(ty) => Some(ty.pat.to_token_stream()), }) .collect::<Vec<_>>(); let arg_ty = inputs.iter().filter_map(|arg| match arg { FnArg::Receiver(_) => None, FnArg::Typed(ty) => Some(ty.ty.to_token_stream()), }); let arg_ty = quote! { ( #(#arg_ty ,)* ) }; let args = if arg_names.is_empty() { quote! { _: () } } else { quote! { ( #(#arg_names,)* ): #arg_ty } }; let ret_ty = quote! { <Self as ::std::ops::FnOnce< #arg_ty >>::Output }; let self_arg = match recv { SelfTy::Owned => quote! { self }, SelfTy::MutRef => quote! { &mut self }, SelfTy::Ref => quote! { &self }, }; let stream = quote! { #[allow(non_camel_case_types)] trait #tr_ident: Sized { type RetTy; fn #ident ( #inputs ) -> Self::RetTy; } impl #impl_generics #tr_ident for #ty #ty_generics #where_clause { type RetTy = #output; fn #ident ( #inputs ) -> <Self as #tr_ident >::RetTy #block } impl #impl_generics ::std::ops::FnOnce< #arg_ty > for #ty #ty_generics #where_clause { type Output = <Self as #tr_ident >::RetTy; extern "rust-call" fn call_once(mut self, #args ) -> #ret_ty { <Self as #tr_ident >:: #ident ( #self_arg #(, #arg_names )* ) } } }; if matches!(recv, SelfTy::Owned) { return stream; } let stream = quote! { #stream impl #impl_generics ::std::ops::FnMut< #arg_ty > for #ty #ty_generics #where_clause { extern "rust-call" fn call_mut(&mut self, #args ) -> #ret_ty { <Self as #tr_ident >:: #ident (self #(, #arg_names )* ) } } }; if matches!(recv, SelfTy::MutRef) { return stream; } quote! { #stream impl #impl_generics ::std::ops::Fn< #arg_ty > for #ty #ty_generics #where_clause { extern "rust-call" fn call(&self, #args ) -> #ret_ty { <Self as #tr_ident >:: #ident (self #(, #arg_names )* ) } } } }