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

extern crate proc_macro;
extern crate syn;
#[macro_use]
extern crate proc_macro_error;
extern crate convert_case;

use convert_case::{Case, Casing as ConvertCasing};
use proc_macro::TokenStream;
use proc_macro2::TokenStream as TokenStream2;
use quote::{format_ident, quote};
use std::str::FromStr;
use syn::punctuated::Punctuated;
use syn::{
    parse_macro_input, token, AttrStyle, Attribute, AttributeArgs, Fields, ItemStruct, Meta,
    NestedMeta, Path, PathSegment,
};

enum Casing {
    Pascal,
    Camel,
    Lower,
    Upper,
    Snake,
    ScreamingSnake,
    Kebab,
    ScreamingKebab,
}

impl FromStr for Casing {
    type Err = String;

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        match s {
            "PascalCase" => Ok(Self::Pascal),
            "CamelCase" => Ok(Self::Camel),
            "LowerCase" => Ok(Self::Lower),
            "UpperCase" => Ok(Self::Upper),
            "SnakeCase" => Ok(Self::Snake),
            "ScreamingSnakeCase" => Ok(Self::ScreamingSnake),
            "KebabCase" => Ok(Self::Kebab),
            "ScreamingKebabCase" => Ok(Self::ScreamingKebab),
            _ => Err(format!(
                "unknown casing: {} try one of {:?}",
                s,
                Casing::all()
            )),
        }
    }
}

impl ToString for Casing {
    fn to_string(&self) -> String {
        let case = match self {
            Self::Camel => "camelCase",
            Self::Pascal => "PascalCase",
            Self::Lower => "lowercase",
            Self::Upper => "UPPERCASE",
            Self::Snake => "snake_case",
            Self::ScreamingSnake => "SCREAMING_SNAKE_CASE",
            Self::Kebab => "kebab-case",
            Self::ScreamingKebab => "SCREAMING-KEBAB-CASE",
        };
        case.to_string()
    }
}

impl Casing {
    const fn all() -> &'static [&'static str] {
        return &[
            "PascalCase",
            "CamelCase",
            "LowerCase",
            "UpperCase",
            "SnakeCase",
            "ScreamingSnakeCase",
            "KebabCase",
            "ScreamingKebabCase",
        ];
    }
}

#[proc_macro_attribute]
pub fn serde_alias(args: TokenStream, input: TokenStream) -> TokenStream {
    let mut input = parse_macro_input!(input as ItemStruct);
    let args = parse_macro_input!(args as AttributeArgs);

    let mut aliases = vec![];

    for arg in args {
        if let NestedMeta::Meta(meta) = arg {
            if let Meta::Path(path) = meta {
                let case_ident = path.get_ident().expect("expected casing");
                let case =
                    Casing::from_str(&case_ident.to_string()).unwrap_or_else(|e| panic!("{}", e));

                aliases.push(case);
            }
        }
    }

    if let Fields::Named(ref mut named) = input.fields {
        for field in &mut named.named {
            let mut punc_attr = Punctuated::new();

            punc_attr.push_value(PathSegment {
                ident: format_ident!("serde"),
                arguments: Default::default(),
            });

            let mut casings = vec![];
            for case in &aliases {
                let convert_casing = match case {
                    Casing::Pascal => Case::Pascal,
                    Casing::Camel => Case::Camel,
                    Casing::Lower => Case::Lower,
                    Casing::Upper => Case::Upper,
                    Casing::Snake => Case::Snake,
                    Casing::ScreamingSnake => Case::ScreamingSnake,
                    Casing::Kebab => Case::Kebab,
                    Casing::ScreamingKebab => Case::Cobol,
                };

                let converted = field
                    .ident
                    .as_ref()
                    .expect("invalid field")
                    .to_string()
                    .to_case(convert_casing);

                let f = format!(r#"alias = "{}""#, converted);
                casings.push(f);
            }

            let res: String = casings.join(",");

            field.attrs.push(Attribute {
                pound_token: token::Pound::default(),
                style: AttrStyle::Outer,
                bracket_token: Default::default(),
                path: Path {
                    leading_colon: None,
                    segments: punc_attr.clone(),
                },
                tokens: TokenStream2::from_str(&format!("({})", res.as_str()))
                    .unwrap_or_else(|a| abort!(punc_attr, format!("Lex error: {}", a))),
            })
        }

        let tokens = quote! {#input};
        return tokens.into();
    }

    abort!(input, "Tuple structs not supported")
}