token_parser_derive/
lib.rs

1#![deny(missing_docs)]
2
3/*!
4Derive macros to automatically implement the `Parsable` trait from `token-parser` for tuple structs (unnamed fields).
5
6Supports sequential parsing via `parse_list` (`Parsable` derive) or symbol parsing via `FromStr` (`SymbolParsable` derive).
7*/
8
9use quote::quote;
10use syn::{
11    Data, DeriveInput, Fields, GenericParam, Generics, TypeParamBound, parse_macro_input,
12    parse_quote,
13};
14
15/// Derive the `Parsable` trait by parsing all unnamed fields in order using the `Parsable` trait.
16///
17/// # Panics
18///
19/// Panics if the input is not a struct with unnamed fields.
20#[proc_macro_derive(Parsable)]
21pub fn derive_default_parsable(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
22    derive_parsable(input, false)
23}
24
25/// Derive the `Parsable` trait by parsing unnamed fields using the `FromStr` trait.
26///
27/// Parses the entire `name` string into each field.
28///
29/// # Panics
30///
31/// Panics if the input is not a struct with unnamed fields.
32#[proc_macro_derive(SymbolParsable)]
33pub fn derive_symbol_parsable(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
34    derive_parsable(input, true)
35}
36
37fn add_trait_bounds(mut generics: Generics, bound: TypeParamBound) -> Generics {
38    for param in &mut generics.params {
39        if let GenericParam::Type(ref mut type_param) = *param {
40            type_param.bounds.push(bound.clone());
41        }
42    }
43    generics
44}
45
46fn derive_parsable(input: proc_macro::TokenStream, symbol: bool) -> proc_macro::TokenStream {
47    let input = parse_macro_input!(input as DeriveInput);
48    let name = input.ident;
49
50    let trait_bound = if symbol {
51        parse_quote!(std::str::FromStr)
52    } else {
53        parse_quote!(token_parser::Parsable)
54    };
55
56    let generics = add_trait_bounds(input.generics.clone(), trait_bound);
57    let (_, ty_generics, where_clause) = generics.split_for_impl();
58
59    let mut generics = input.generics;
60    generics.params.push(parse_quote!(C: token_parser::Context));
61    let (impl_generics, _, _) = generics.split_for_impl();
62
63    let Data::Struct(data) = input.data else {
64        panic!("Deriving parser is only available for structs");
65    };
66
67    match data.fields {
68        Fields::Unnamed(fields) => {
69            let expression = if symbol {
70                quote! {
71                    name.parse()
72                        .map_err(|_| token_parser::Error::StringParsing)?
73                }
74            } else {
75                quote!(parser.parse_next(context)?)
76            };
77
78            let expressions = fields.unnamed.into_iter().map(|_| &expression);
79
80            let method = if symbol {
81                quote! {
82                    fn parse_symbol(name: Box<str>, context: &C) -> token_parser::Result<Self>
83                }
84            } else {
85                quote! {
86                    fn parse_list(parser: &mut token_parser::Parser, context: &C) -> token_parser::Result<Self>
87                }
88            };
89
90            let expanded = quote! {
91                impl #impl_generics token_parser::Parsable<C> for #name #ty_generics #where_clause {
92                    #method
93                    {
94                        Ok(#name(#( #expressions, )*))
95                    }
96                }
97            };
98
99            proc_macro::TokenStream::from(expanded)
100        }
101        _ => panic!("Deriving parser is only available for tuple structs"),
102    }
103}
token_parser_derive/lib.rs

token_parser_derive/
lib.rs
