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use proc_macro::TokenStream; use proc_macro_error::*; use syn; use quote::quote; struct Flag { value: TokenStream, name: String, method_name: Option<syn::Ident>, } impl Flag { fn method_name(&self) -> syn::Ident { if let Some(ident) = &self.method_name { ident.clone() } else { syn::Ident::new(&self.name, proc_macro2::Span::call_site()) } } } enum DebugMode { None, Standard, Compact } struct FlagImpl { struct_name: syn::Ident, backing_field_name: syn::Member, flags: Vec<Flag>, debug_mode: DebugMode } fn get_value(lit: &syn::Lit, value_type: &syn::Type) -> TokenStream { use syn::Lit::*; let result = match lit { Int(_) => quote!{ #lit as #value_type }, Str(s) => { let expr: syn::Expr = match syn::parse_str(&s.value()) { Ok(expr) => expr, _ => { abort!(lit, "String must contain a valid expression"); } }; quote! { (#expr) as #value_type } }, _ => abort!(lit, "Bad value, must be an integer literal or string.") }; result.into() } fn get_name(lit: &syn::Lit) -> String { use syn::Lit::*; match &lit { Str(s) => s.value(), _ => panic!("Bad name") } } fn get_method_name(lit: &syn::Lit) -> syn::Ident { use syn::{Lit::*, Ident}; match &lit { Str(s) => Ident::new(&s.value(), lit.span()), _ => panic!("Bad method_name") } } fn parse_flag(attr: syn::Meta, value_type: &syn::Type) -> Flag { let mut name = None; let mut value = None; let mut method_name = None; if let syn::Meta::List(attr) = &attr { use syn::{Meta::NameValue, NestedMeta::Meta}; let args = &attr.nested; for arg in args { if let Meta(NameValue(m)) = arg { if let Some(n) = m.path.get_ident() { match n.to_string().as_str() { "name" => name = Some(get_name(&m.lit)), "value" => value = Some(get_value(&m.lit, value_type)), "method_name" => method_name = Some(get_method_name(&m.lit)), s => abort!(arg, r#"Unknown configuration option "{}". Expected one of [name, value, method_name]"#, s) } } } } } if let (Some(name), Some(value)) = (name, value) { Flag { name, value, method_name } } else { abort!(attr, "Missing name or value argument for flag.") } } fn get_backing_field(input: &syn::DeriveInput) -> (syn::Member, syn::Field) { let st = if let syn::Data::Struct(ds) = &input.data { ds } else { abort!(input, "Must be a struct") }; let candidates: Vec<(syn::Member, &syn::Field)> = match &st.fields { syn::Fields::Named(named) => { named.named.iter() .filter(|f| f.attrs.iter().any(|a| a.path.is_ident("flag_backing_field"))) .map(|f| (syn::Member::Named(f.ident.clone().unwrap()), f)) .collect() }, syn::Fields::Unnamed(unnamed) => { unnamed.unnamed.iter() .enumerate() .filter(|(_, f)| f.attrs.iter().any(|a| a.path.is_ident("flag_backing_field"))) .map(|(i, f)| (syn::Member::Unnamed(syn::Index::from(i)), f)) .collect() }, _ => vec![] }; if candidates.len() == 1 { let (ident, field) = candidates.first().unwrap(); (ident.clone().into(), (*field).clone().into()) } else { abort!(input, r#"Exactly one backing field must have the "flag_backing_field" attribute"#) } } fn parse_impl(input: TokenStream) -> FlagImpl { use syn::Meta::*; let ast: syn::DeriveInput = syn::parse(input).unwrap(); let (backing_field_name, backing_field) = get_backing_field(&ast); let struct_name = ast.ident.clone(); let mut flags = vec![]; let mut debug_mode = DebugMode::None; for attr in ast.attrs { if let Some(name) = attr.path.get_ident() { match name.to_string().as_str() { "flag" => { let meta = attr.parse_meta().unwrap_or_else(|_| abort!(attr, "Bad attribute arguments")); let flag = parse_flag(meta, &backing_field.ty); flags.push(flag); }, "flag_debug" => { let meta = attr.parse_meta(); match meta { Ok(Path(_)) => debug_mode = DebugMode::Standard, Ok(List(ml)) => { if let Some(syn::NestedMeta::Meta(m)) = ml.nested.first() { if ml.nested.len() == 1 && m.path().is_ident("compact") { debug_mode = DebugMode::Compact; continue; } else { abort!(ml, "Bad option for flag_meta attribute"); } } else { debug_mode = DebugMode::Standard; } } _ => abort!(attr, "Bad attribute arguments") } } _ => () } } } FlagImpl { struct_name, backing_field_name, flags, debug_mode } } #[proc_macro_derive(Flags, attributes(flag, flag_backing_field, flag_debug))] #[proc_macro_error] pub fn derive_flags(input: TokenStream) -> TokenStream { let mut flag_impl = parse_impl(input); let backing_field_name = flag_impl.backing_field_name; let struct_name = flag_impl.struct_name; let mut methods = vec![]; let mut debug_fragments = vec![]; for flag in flag_impl.flags.drain(..) { use quote::format_ident; let name = flag.name.clone(); let method_name = flag.method_name(); let value: proc_macro2::TokenStream = flag.value.into(); match flag_impl.debug_mode { DebugMode::None => (), DebugMode::Standard => { debug_fragments.push(quote!{ .field(stringify!(#method_name), &self.#method_name()) }); }, DebugMode::Compact => { debug_fragments.push(quote!{ if self.#method_name() { dbg.entry(&#name); } }); } } let setter_name = format_ident!("set_{}", method_name); let exclusive_name = format_ident!("only_{}", method_name); let flag_methods = quote!{ pub fn #method_name(&self) -> bool { self.#backing_field_name & (#value) == (#value) } pub fn #exclusive_name(&self) -> bool { self.#backing_field_name | (#value) == (#value) } pub fn #setter_name(&mut self, value: bool) -> &Self { if value { self.#backing_field_name |= (#value); } else { self.#backing_field_name &= !(#value) } self } }; methods.push(flag_methods); } let main_impl = quote!{ impl #struct_name { #(#methods)* } }; let debug_impl = match flag_impl.debug_mode { DebugMode::None => quote!{}, DebugMode::Standard => quote!{ impl core::fmt::Debug for #struct_name { fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result { f.debug_struct(stringify!(#struct_name)) #(#debug_fragments)* .finish() } } }, DebugMode::Compact => quote!{ impl core::fmt::Debug for #struct_name { fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result { write!(f, "{} ", stringify!(#struct_name))?; let mut dbg = f.debug_set(); #(#debug_fragments)* dbg.finish() } } } }; (quote!{ #main_impl #debug_impl }).into() }