diff options
Diffstat (limited to 'src/lib.rs')
| -rw-r--r-- | src/lib.rs | 177 |
1 files changed, 175 insertions, 2 deletions
@@ -1,4 +1,177 @@ -#[proc_macro_derive(Get)] +#![deny(clippy::use_self)] + +#[proc_macro_derive(Get, attributes(get))] pub fn get(input: proc_macro::TokenStream) -> proc_macro::TokenStream { - todo!() + let parsed_input = syn::parse_macro_input!(input as syn::DeriveInput); + get::expand(&parsed_input, false).unwrap().into() +} + +mod get { + + use proc_macro2::{Span, TokenStream}; + use quote::{format_ident, quote, ToTokens}; + use syn::{ + parse::Parser, punctuated::Punctuated, Attribute, Data, DeriveInput, Expr, Field, Fields, + Index, Lit, Member, Meta, MetaNameValue, Token, Type, + }; + + #[derive(Default)] + struct GetAttribute { + method: Option<String>, + } + + #[derive(Debug, Clone)] + enum GetNameValue { + Method(String), + } + + pub fn expand( + input: &DeriveInput, + is_copy: bool, + ) -> Result<TokenStream, Box<dyn std::error::Error>> { + let Data::Struct(target) = &input.data else { + return Err("expected struct as derive input".into()) + }; + let getters = match &target.fields { + Fields::Unnamed(fields) => expand_for_tuple_struct(fields.unnamed.iter(), is_copy)?, + Fields::Named(fields) => expand_for_struct(fields.named.iter(), is_copy)?, + _ => return Err("can not generate getters on a unit struct".into()), + }; + let (impl_generics, ty_generics, where_clause) = &input.generics.split_for_impl(); + let struct_name = &input.ident; + Ok(quote! { + #[automatically_derived] + impl #impl_generics #struct_name #ty_generics #where_clause { + #getters + } + }) + } + + fn expand_for_struct<'a>( + fields: impl Iterator<Item = &'a Field>, + is_copy: bool, + ) -> Result<TokenStream, Box<dyn std::error::Error>> { + let mut tokens = TokenStream::new(); + for field in fields { + let default_method_name = field.ident.as_ref().cloned().unwrap().to_string(); + let method_name = field + .attrs + .iter() + .find(|attr| attr.path().is_ident("get")) + .cloned() + .map_or(Ok(default_method_name.clone()), |attr| { + GetAttribute::try_from(attr) + .map(|get_attr| get_attr.method.unwrap_or(default_method_name.clone())) + })?; + let getter = expand_getter( + field, + Member::Named(field.ident.as_ref().unwrap().clone()), + method_name.as_str(), + is_copy, + ); + getter.to_tokens(&mut tokens); + } + Ok(tokens) + } + + fn expand_for_tuple_struct<'a>( + fields: impl Iterator<Item = &'a Field>, + is_copy: bool, + ) -> Result<TokenStream, Box<dyn std::error::Error>> { + let mut tokens = TokenStream::new(); + for (i, field) in fields.enumerate() { + let attr: GetAttribute = field + .attrs + .iter() + .find(|a| a.path().is_ident("get")) + .cloned() + .ok_or("tuple fields are required to have an attribute")? + .try_into()?; + let method_name = attr + .method + .ok_or("tuple field attributes must specify the method name")?; + let getter = expand_getter( + field, + Member::Unnamed(Index { + index: i as u32, + span: Span::call_site(), + }), + method_name.as_str(), + is_copy, + ); + getter.to_tokens(&mut tokens); + } + Ok(tokens) + } + + fn expand_getter( + field: &Field, + field_name: Member, + method_name: &str, + is_copy: bool, + ) -> TokenStream { + let method_name = format_ident!("{method_name}"); + let field_type = &field.ty; + let field_lifetime = match &field.ty { + Type::Reference(type_ref) => Some(&type_ref.lifetime), + _ => None, + }; + let reference = (!is_copy).then(|| quote! { & }); + quote! { + pub fn + #method_name + ( #reference #field_lifetime self ) + -> #reference #field_type { + #reference self.#field_name + } + } + } + + // This method might seem overly complicated but it will make it easy to add new fields to the + // GetAttribute struct in the future! + + impl TryFrom<Attribute> for GetAttribute { + type Error = Box<dyn std::error::Error>; + fn try_from(attr: Attribute) -> Result<Self, Self::Error> { + if attr.path().is_ident("get") { + if let Meta::List(meta_list) = &attr.meta { + if let Ok(meta_name_values) = + Punctuated::<MetaNameValue, Token![,]>::parse_terminated + .parse(meta_list.tokens.clone().into()) + { + let get_name_values = meta_name_values + .iter() + .map(|n| n.try_into()) + .collect::<Result<Vec<GetNameValue>, _>>()?; + return Ok(get_name_values.into_iter().fold( + Self::default(), + |_, g| match g { + GetNameValue::Method(name) => Self { method: Some(name) }, + }, + )); + } + } + } + Err("failed to parse attribute".into()) + } + } + + // The same applies here. + + impl<'a> TryFrom<&'a MetaNameValue> for GetNameValue { + type Error = Box<dyn std::error::Error>; + fn try_from(meta: &'a MetaNameValue) -> Result<Self, Self::Error> { + if let Some(name) = meta.path.get_ident().map(|i| i.to_string()) { + if let Expr::Lit(expr_lit) = &meta.value { + if let Lit::Str(s) = &expr_lit.lit { + let value = s.value(); + if let "method" = name.as_str() { + return Ok(Self::Method(value)); + }; + } + } + } + Err("invalid name value list in attribute".into()) + } + } } |