1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167

//! # enum-stringify
//!
//! Derive [`std::fmt::Display`], [`std::str::FromStr`], [`TryFrom<&str>`] and
//! [`TryFrom<String>`] with a simple derive macro: [`EnumStringify`].

use proc_macro::TokenStream;
use quote::quote;

/// Derive [`std::fmt::Display`], [`std::str::FromStr`], [`TryFrom<&str>`] and
/// [`TryFrom<String>`] for an enum.
///
/// They simply take the name of the enum variant and convert it to a string.
///
/// # Example
///
/// ```
/// use enum_stringify::EnumStringify;
/// use std::str::FromStr;
///
/// #[derive(EnumStringify, Debug, PartialEq)]
/// enum Numbers {
///    One,
///    Two,
/// }
///
/// assert_eq!(Numbers::One.to_string(), "One");
/// assert_eq!(Numbers::Two.to_string(), "Two");
///
///
/// assert_eq!(Numbers::try_from("One").unwrap(), Numbers::One);
/// assert_eq!(Numbers::try_from("Two").unwrap(), Numbers::Two);
///
/// assert!(Numbers::try_from("Three").is_err());
/// ```
///
/// # Details
///
/// The implementations of the above traits corresponds to this:
///
/// ```rust, no_run
/// enum Numbers {
///   One,
///   Two,
/// }
///
/// impl std::fmt::Display for Numbers {
///     fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
///         match self {
///             Self::One => write!(f, "One"),
///             Self::Two => write!(f, "Two"),
///         }
///     }
/// }
///
/// impl TryFrom<&str> for Numbers {
///     type Error = ();
///
///     fn try_from(s: &str) -> Result<Self, Self::Error> {
///         match s {    
///             "One" => Ok(Self::One),
///             "Two" => Ok(Self::Two),
///             _ => Err(()),
///         }
///     }
/// }
///
/// impl TryFrom<String> for Numbers {
///     type Error = ();
///         
///     fn try_from(s: String) -> Result<Self, Self::Error> {
///         s.as_str().try_into()
///     }
/// }
///
/// impl std::str::FromStr for Numbers {
///     type Err = ();
///
///     fn from_str(s: &str) -> Result<Self, Self::Err> {
///         s.try_into()
///     }
/// }
/// ```
#[proc_macro_derive(EnumStringify)]
pub fn enum_stringify(input: TokenStream) -> TokenStream {
    let ast = syn::parse(input).unwrap();
    impl_enum_to_string(&ast)
}

fn impl_enum_to_string(ast: &syn::DeriveInput) -> TokenStream {
    let name = &ast.ident;
    let variants = match ast.data {
        syn::Data::Enum(ref e) => &e.variants,
        _ => panic!("EnumToString only works with Enums"),
    };

    let names = variants.iter().map(|v| &v.ident).collect::<Vec<_>>();

    let mut gen = impl_display(name, &names);
    gen.extend(impl_from_str(name, &names));
    gen.extend(impl_from_string(name));
    gen.extend(impl_from_str_trait(name));

    gen
}

/// Implementation of [`std::fmt::Display`].
fn impl_display(name: &syn::Ident, names: &Vec<&syn::Ident>) -> TokenStream {
    let gen = quote! {
        impl std::fmt::Display for #name {
            fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
                match self {
                    #(Self::#names => write!(f, stringify!(#names))),*
                }
            }
        }
    };

    gen.into()
}

/// Implementation of [`TryFrom<&str>`].
fn impl_from_str(name: &syn::Ident, names: &Vec<&syn::Ident>) -> TokenStream {
    let gen = quote! {
        impl TryFrom<&str> for #name {
            type Error = ();

            fn try_from(s: &str) -> Result<Self, Self::Error> {
                match s {
                    #(stringify!(#names) => Ok(Self::#names),)*
                    _ => Err(()),
                }
            }
        }
    };

    gen.into()
}

/// Implementation of [`TryFrom<String>`].
fn impl_from_string(name: &syn::Ident) -> TokenStream {
    let gen = quote! {
        impl TryFrom<String> for #name {
            type Error = ();

            fn try_from(s: String) -> Result<Self, Self::Error> {
                s.as_str().try_into()
            }
        }
    };

    gen.into()
}

/// Implementation of [`std::str::FromStr`].
fn impl_from_str_trait(name: &syn::Ident) -> TokenStream {
    let gen = quote! {
        impl std::str::FromStr for #name {
            type Err = ();

            fn from_str(s: &str) -> Result<Self, Self::Err> {
                s.try_into()
            }
        }
    };

    gen.into()
}