enum_variant_macros_macros 0.3.1

Macros for enum_variant_macros
Documentation 
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

//! Proc macros for derive_try_from
//!
//! Do not link to this.
//! This library is solely to provide proc macros.
use proc_macro2::TokenStream;
use quote::quote;
use quote::ToTokens;
use std::collections::HashMap;
use syn::spanned::Spanned;
use syn::{parse_macro_input, Data, DeriveInput, Fields};

/// Generates TryFrom for each variant of enum.
#[proc_macro_derive(TryFromVariants)]
pub fn try_from_variants(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
    let input = parse_macro_input!(input as DeriveInput);

    let output = from_variants_proc(input, "TryFromVariants", &try_from_quote);

    output.unwrap_or_else(syn::Error::into_compile_error).into()
}

/// Generates From for each variant of enum.
#[proc_macro_derive(FromVariants)]
pub fn from_variants(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
    let input = parse_macro_input!(input as DeriveInput);

    let output = from_variants_proc(input, "FromVariants", &variant_from_quote);

    output.unwrap_or_else(syn::Error::into_compile_error).into()
}

fn from_variants_proc<F>(
    input: DeriveInput,
    macro_name: &str,
    quote_fn: F,
) -> syn::Result<TokenStream>
where
    F: Fn(&syn::Ident, &syn::Ident, &syn::Field) -> TokenStream,
{
    let input_name = &input.ident;

    match input.data {
        Data::Enum(enum_data) => {
            let mut stream = TokenStream::new();
            let mut implemented_types = HashMap::new();
            implemented_types.reserve(enum_data.variants.len());
            for variant in enum_data.variants {
                stream.extend(generate_variant_froms(
                    input_name,
                    &variant,
                    macro_name,
                    &quote_fn,
                    &mut implemented_types,
                )?);
            }
            Ok(stream)
        }
        _ => Err(syn::Error::new(
            input.span(),
            format!("Derive {macro_name} for {input_name} failed. Must be an enum."),
        )),
    }
}

fn generate_variant_froms<F>(
    enum_name: &syn::Ident,
    variant: &syn::Variant,
    macro_name: &str,
    quote_fn: F,
    implemented_types: &mut HashMap<syn::Field, syn::Ident>,
) -> syn::Result<TokenStream>
where
    F: Fn(&syn::Ident, &syn::Ident, &syn::Field) -> TokenStream,
{
    let member_data = match &variant.fields {
        Fields::Unnamed(fields) => &fields.unnamed,
        _ => {
            return Err(syn::Error::new(
                variant.fields.span(),
                format!(
                    "{} can only use unnamed members, failed for {}::{}",
                    macro_name, enum_name, variant.ident
                ),
            ))
        }
    };
    // Check only contains 1 element
    if member_data.len() != 1 {
        return Err(syn::Error::new(
            member_data.span(),
            format!(
                "{} failed for {}::{}, does not currently support variants that are larger than 1",
                macro_name, enum_name, variant.ident
            ),
        ));
    }

    let variant = &variant.ident;
    let wrapped_type = member_data.first().unwrap();

    if let Some(original) = implemented_types.insert(wrapped_type.clone(), variant.clone()) {
        Err(syn::Error::new(
            member_data.span(),
            format!(
                "Repeat of variant for type {} in variant {}::{}. Already defined with {}::{}",
                wrapped_type.ty.to_token_stream(),
                enum_name,
                variant,
                enum_name,
                original
            ),
        ))
    } else {
        Ok(quote_fn(enum_name, variant, wrapped_type))
    }
}

fn try_from_quote(
    enum_name: &syn::Ident,
    variant: &syn::Ident,
    wrapped_type: &syn::Field,
) -> TokenStream {
    quote! {
    impl TryFrom<#enum_name> for #wrapped_type {
        type Error = ::enum_variant_macros::VariantCastError;

        fn try_from(value: #enum_name) -> ::std::result::Result<Self, Self::Error> {
            match value {
                #enum_name::#variant(n) => Ok(n),
                _ => Err(::enum_variant_macros::VariantCastError {
                    enum_type: stringify!(#enum_name),
                    exp_type: stringify!(#wrapped_type),
                    variant_name: value.into(),
                }),
            }
        }
    }
    }
}

fn variant_from_quote(
    enum_name: &syn::Ident,
    variant: &syn::Ident,
    wrapped_type: &syn::Field,
) -> TokenStream {
    quote! {
        impl From<#wrapped_type> for #enum_name {
            fn from(value: #wrapped_type) -> #enum_name {
                #enum_name::#variant(value)
            }
        }
    }
}