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extern crate proc_macro; extern crate syn; #[macro_use] extern crate quote; use proc_macro::TokenStream; use quote::ToTokens; use syn::{Data, DeriveInput, Field, Fields, Variant}; #[proc_macro_derive(EnumError)] pub fn enum_error(input: TokenStream) -> TokenStream { let ast = into_ast(input); let froms = impl_into_enum(&ast); let display = impl_display(&ast); let error = impl_error(&ast); let tokens = quote!{ #froms #display #error }; tokens.into() } #[proc_macro_derive(IntoEnum)] pub fn into_enum(input: TokenStream) -> TokenStream { let ast = into_ast(input); let froms = impl_into_enum(&ast); let tokens = quote!{ #froms }; tokens.into() } #[proc_macro_derive(NewType)] pub fn newtype(input: TokenStream) -> TokenStream { let ast = into_ast(input); let from = impl_newtype_from(&ast); let deref = impl_newtype_deref(&ast); let tokens = quote!{ #from #deref }; tokens.into() } fn into_ast(input: TokenStream) -> DeriveInput { syn::parse(input).unwrap() } fn get_enum_variants(ast: &DeriveInput) -> Vec<&Variant> { match ast.data { Data::Enum(ref inner) => inner.variants.iter().collect(), Data::Struct(_) => unreachable!("Structs are not supported"), Data::Union(_) => unreachable!("Unions are not supported"), } } fn get_basetype(ast: &DeriveInput) -> &Field { match ast.data { Data::Enum(_) => unreachable!("Enums are not supported"), Data::Union(_) => unreachable!("Unions are not supported"), Data::Struct(ref ds) => { match ds.fields { Fields::Named(_) => unreachable!("Must be tuple struct"), Fields::Unnamed(ref t) => { if t.unnamed.len() > 1 { unreachable!("Must be one type"); } &t.unnamed[0] } Fields::Unit => unreachable!("Must be tuple struct"), } } } } fn impl_into_enum(ast: &DeriveInput) -> Box<ToTokens> { let name = &ast.ident; let variants = get_enum_variants(&ast); let (impl_generics, ty_generics, where_clause) = ast.generics.split_for_impl(); let impls = variants.iter().map(|var| { let v = &var.ident; let cont = match var.fields { Fields::Unnamed(ref c) => &c.unnamed, _ => unreachable!(), }; assert!(cont.len() == 1, "Single tuple is required"); let ctype = &cont[0].ty; quote!{ impl #impl_generics From<#ctype> for #name #ty_generics #where_clause { fn from(val: #ctype) -> Self { #name::#v(val) } } } }); Box::new(quote!{ #(#impls)* }) } fn impl_newtype_from(ast: &DeriveInput) -> Box<ToTokens> { let name = &ast.ident; let field = get_basetype(&ast); let base = &field.ty; let (impl_generics, ty_generics, where_clause) = ast.generics.split_for_impl(); Box::new( quote!{ impl #impl_generics From<#base> for #name #ty_generics #where_clause { fn from(val: #base) -> Self { #name(val) } } impl #impl_generics Into<#base> for #name #ty_generics #where_clause { fn into(self) -> #base { self.0 } } } ) } fn impl_newtype_deref(ast: &DeriveInput) -> Box<ToTokens> { let name = &ast.ident; let field = get_basetype(&ast); let base = &field.ty; let (impl_generics, ty_generics, where_clause) = ast.generics.split_for_impl(); Box::new( quote!{ impl #impl_generics ::std::ops::Deref for #name #ty_generics #where_clause { type Target = #base; fn deref(&self) -> &Self::Target { &self.0 } } impl #impl_generics ::std::ops::DerefMut for #name #ty_generics #where_clause { fn deref_mut(&mut self) -> &mut Self::Target { &mut self.0 } } } ) } fn impl_error(ast: &DeriveInput) -> Box<ToTokens> { let name = &ast.ident; let variants = get_enum_variants(&ast); let (impl_generics, ty_generics, where_clause) = ast.generics.split_for_impl(); let snips = variants.iter().map(|var| { let v = &var.ident; quote!{ #name::#v(ref err) => err.description() } }); Box::new( quote!{ impl #impl_generics ::std::error::Error for #name #ty_generics #where_clause { fn description(&self) -> &str { match *self { #(#snips), * } } } } ) } fn impl_display(ast: &DeriveInput) -> Box<ToTokens> { let name = &ast.ident; let variants = get_enum_variants(&ast); let (impl_generics, ty_generics, where_clause) = ast.generics.split_for_impl(); let snips = variants.iter().map(|var| { let v = &var.ident; quote!{ #name::#v(ref err) => err.fmt(f) } }); Box::new( quote!{ impl #impl_generics ::std::fmt::Display for #name #ty_generics #where_clause { fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result { match *self { #(#snips), * } } } } ) }