variant_set_derive/
lib.rs

1#![warn(clippy::all, clippy::pedantic)]
2
3use quote::{format_ident, quote};
4use syn::{parse_macro_input, Data, DeriveInput};
5
6/// Derives a `_Variant` enum for the given enum, and derives the `VariantEnum` trait.
7///
8/// The `VariantEnum` trait is used to convert an enum into a variant enum, which is an enum that has a variant for
9/// each variant of the input enum, but without any data. This is used for the
10/// `VariantSet<T>` type, which is a set of variants of type T.
11///
12/// # Panics
13///
14/// Panics if the input is not an enum.
15#[proc_macro_derive(VariantEnum)]
16pub fn derive_variant_enum(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
17    let input = parse_macro_input!(input as DeriveInput);
18
19    let name = &input.ident;
20    let variants_enum_name = format_ident!("{}Variant", &input.ident);
21
22    let variants = match &input.data {
23        Data::Enum(data) => &data.variants,
24        _ => panic!("VariantEnum can only be derived for enums"),
25    };
26
27    let variant_idents: Vec<_> = variants.iter().map(|variant| &variant.ident).collect();
28
29    let enum_variants = variant_idents.iter().map(|variant| {
30        quote! {
31            #variant
32        }
33    });
34
35    let variant_cases = variants.iter().map(|variant| {
36        let variant_name = &variant.ident;
37        match &variant.fields {
38            syn::Fields::Unit => {
39                quote! {
40                    #name::#variant_name => #variants_enum_name::#variant_name,
41                }
42            }
43            syn::Fields::Named(_) => {
44                quote! {
45                    #name::#variant_name { .. } => #variants_enum_name::#variant_name,
46                }
47            }
48            syn::Fields::Unnamed(_) => {
49                quote! {
50                    #name::#variant_name(..) => #variants_enum_name::#variant_name,
51                }
52            }
53        }
54    });
55
56    let expanded = quote! {
57        #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
58        pub enum #variants_enum_name {
59            #(#enum_variants),*
60        }
61
62        impl From<#name> for #variants_enum_name {
63            fn from(value: #name) -> Self {
64                <#name as variant_set::VariantEnum>::variant(&value)
65            }
66        }
67
68        impl variant_set::VariantEnum for #name {
69            type Variant = #variants_enum_name;
70
71            fn variant(&self) -> Self::Variant {
72                match self {
73                    #(#variant_cases)*
74                }
75            }
76        }
77    };
78
79    proc_macro::TokenStream::from(expanded)
80}
variant_set_derive/lib.rs

variant_set_derive/
lib.rs
