normalize_derive/
lib.rs

1//! Derive macros for normalize.
2
3use proc_macro::TokenStream;
4use quote::quote;
5use syn::{Data, DeriveInput, Fields, parse_macro_input};
6
7/// Derive the `Merge` trait for a struct.
8///
9/// Generates an implementation that calls `.merge()` on each field.
10/// All fields must implement `Merge`.
11///
12/// # Example
13///
14/// ```ignore
15/// use normalize::Merge;
16///
17/// #[derive(Merge)]
18/// struct Config {
19///     enabled: bool,
20///     name: Option<String>,
21/// }
22/// ```
23#[proc_macro_derive(Merge)]
24pub fn derive_merge(input: TokenStream) -> TokenStream {
25    let input = parse_macro_input!(input as DeriveInput);
26    let name = &input.ident;
27    let generics = &input.generics;
28    let (impl_generics, ty_generics, where_clause) = generics.split_for_impl();
29
30    let merge_impl = match &input.data {
31        Data::Struct(data) => match &data.fields {
32            Fields::Named(fields) => {
33                let field_merges = fields.named.iter().map(|f| {
34                    let field_name = &f.ident;
35                    quote! {
36                        #field_name: ::normalize_core::Merge::merge(self.#field_name, other.#field_name)
37                    }
38                });
39                quote! {
40                    Self {
41                        #(#field_merges),*
42                    }
43                }
44            }
45            Fields::Unnamed(fields) => {
46                let field_merges = (0..fields.unnamed.len()).map(|i| {
47                    let index = syn::Index::from(i);
48                    quote! {
49                        ::normalize_core::Merge::merge(self.#index, other.#index)
50                    }
51                });
52                quote! {
53                    Self(#(#field_merges),*)
54                }
55            }
56            Fields::Unit => quote! { Self },
57        },
58        Data::Enum(_) => {
59            return syn::Error::new_spanned(&input, "Merge cannot be derived for enums")
60                .to_compile_error()
61                .into();
62        }
63        Data::Union(_) => {
64            return syn::Error::new_spanned(&input, "Merge cannot be derived for unions")
65                .to_compile_error()
66                .into();
67        }
68    };
69
70    let expanded = quote! {
71        impl #impl_generics ::normalize_core::Merge for #name #ty_generics #where_clause {
72            fn merge(self, other: Self) -> Self {
73                #merge_impl
74            }
75        }
76    };
77
78    TokenStream::from(expanded)
79}
normalize_derive/lib.rs

normalize_derive/
lib.rs
