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core_macros/
lib.rs

1use proc_macro::TokenStream;
2use quote::quote;
3use syn::{parse_macro_input, Data, DeriveInput, Fields};
4
5#[proc_macro_derive(WithParams, attributes(params))]
6pub fn derive_with_params(input: TokenStream) -> TokenStream {
7    let input = parse_macro_input!(input as DeriveInput);
8    let name = &input.ident;
9
10    // Find the field marked with #[params]
11    let params_field = match &input.data {
12        Data::Struct(data) => match &data.fields {
13            Fields::Named(fields) => fields.named.iter().find(|field| {
14                field
15                    .attrs
16                    .iter()
17                    .any(|attr| attr.path().is_ident("params"))
18            }),
19            _ => panic!("WithParams can only be derived for structs with named fields"),
20        },
21        _ => panic!("WithParams can only be derived for structs"),
22    };
23
24    let params_field = params_field.expect("No field marked with #[params] found");
25    let params_field_name = &params_field.ident;
26
27    let expanded = quote! {
28        impl #name {
29            pub fn param(&self, key: &str) -> Option<&toml::Value> {
30                self.#params_field_name.as_ref()?.get(key)
31            }
32        }
33    };
34
35    TokenStream::from(expanded)
36}