enum_display_macro/
lib.rs

1use convert_case::{Case, Casing};
2use proc_macro::{self, TokenStream};
3use quote::quote;
4use syn::{parse_macro_input, DeriveInput};
5
6fn parse_case_name(case_name: &str) -> Case {
7    match case_name {
8        "Upper" => Case::Upper,
9        "Lower" => Case::Lower,
10        "Title" => Case::Title,
11        "Toggle" => Case::Toggle,
12        "Camel" => Case::Camel,
13        "Pascal" => Case::Pascal,
14        "UpperCamel" => Case::UpperCamel,
15        "Snake" => Case::Snake,
16        "UpperSnake" => Case::UpperSnake,
17        "ScreamingSnake" => Case::ScreamingSnake,
18        "Kebab" => Case::Kebab,
19        "Cobol" => Case::Cobol,
20        "UpperKebab" => Case::UpperKebab,
21        "Train" => Case::Train,
22        "Flat" => Case::Flat,
23        "UpperFlat" => Case::UpperFlat,
24        "Alternating" => Case::Alternating,
25        _ => panic!("Unrecognized case name: {}", case_name),
26    }
27}
28
29#[proc_macro_derive(EnumDisplay, attributes(enum_display))]
30pub fn derive(input: TokenStream) -> TokenStream {
31    // Parse the input tokens into a syntax tree
32    let DeriveInput {
33        ident, data, attrs, ..
34    } = parse_macro_input!(input);
35
36    // Should we transform the case of the enum variants?
37    let mut case_transform: Option<Case> = None;
38
39    // Find the enum_display attribute
40    for attr in attrs.into_iter() {
41        if attr.path.is_ident("enum_display") {
42            let meta = attr.parse_meta().unwrap();
43            if let syn::Meta::List(list) = meta {
44                for nested in list.nested {
45                    if let syn::NestedMeta::Meta(syn::Meta::NameValue(name_value)) = nested {
46                        if name_value.path.is_ident("case") {
47                            if let syn::Lit::Str(lit_str) = name_value.lit {
48                                // Set the case transform
49                                case_transform = Some(parse_case_name(lit_str.value().as_str()));
50                            }
51                        }
52                    }
53                }
54            }
55        }
56    }
57
58    // Build the match arms
59    let variants = match data {
60        syn::Data::Enum(syn::DataEnum { variants, .. }) => variants,
61        _ => panic!("EnumDisplay can only be derived for enums"),
62    }
63    .into_iter()
64    .map(|variant| {
65        let ident = variant.ident;
66        let ident_str = if case_transform.is_some() {
67            ident.to_string().to_case(case_transform.unwrap())
68        } else {
69            ident.to_string()
70        };
71
72        match variant.fields {
73            syn::Fields::Named(_) => quote! {
74                #ident { .. } => #ident_str,
75            },
76            syn::Fields::Unnamed(_) => quote! {
77                #ident(..) => #ident_str,
78            },
79            syn::Fields::Unit => quote! {
80                #ident => #ident_str,
81            },
82        }
83    });
84
85    // #[allow(unused_qualifications)] is needed
86    // due to https://github.com/SeedyROM/enum-display/issues/1
87    // Possibly related to https://github.com/rust-lang/rust/issues/96698
88    let output = quote! {
89        #[automatically_derived]
90        #[allow(unused_qualifications)]
91        impl ::core::fmt::Display for #ident {
92            fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
93                ::core::fmt::Formatter::write_str(
94                    f,
95                    match self {
96                        #(#ident::#variants)*
97                    },
98                )
99            }
100        }
101    };
102    output.into()
103}
enum_display_macro/lib.rs

enum_display_macro/
lib.rs
