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

extern crate proc_macro;

use proc_macro::TokenStream;
use quote::quote;
use syn::Data;
use syn::DeriveInput;
use syn::{
    punctuated::Punctuated, token::Comma, Attribute, Field, Fields, FieldsNamed, Ident, Lit, Meta,
    NestedMeta,
};

struct FieldArgs {
    env: Option<Lit>,
    default: Option<Lit>,
}

struct FieldInit {
    name: Ident,
    args: FieldArgs,
}

impl FieldInit {
    fn parse_env_and_default(&self, v: &Lit, d: &Lit) -> quote::__private::TokenStream {
        let name = self.name.clone();

        quote! {
            #name: if let Ok(r) = std::env::var(#v) {
                r.parse().map_err(|_| Error::EnvParse(#v, r))?
            } else {
                #d.to_string().parse().map_err(|_| Error::DefaultParse(stringify!(#name), stringify!(#d)))?
            }
        }
    }

    fn parse_env_only(&self, v: &Lit) -> quote::__private::TokenStream {
        let name = self.name.clone();

        quote! {
            #name: if let Ok(r) = std::env::var(#v) {
                r.parse().map_err(|_| Error::EnvParse(#v, r))?
            } else {
                return Err(Error::MissingEnv(#v));
            }
        }
    }

    fn parse_default_only(&self, d: &Lit) -> quote::__private::TokenStream {
        let name = self.name.clone();

        quote! { #name: #d.to_string().parse().map_err(|_| Error::DefaultParse(stringify!(#name), stringify!(#d)))? }
    }
}

impl quote::ToTokens for FieldInit {
    fn to_tokens(&self, tokens: &mut quote::__private::TokenStream) {
        let gen = if let Some(v) = &self.args.env {
            if let Some(d) = &self.args.default {
                self.parse_env_and_default(v, d)
            } else {
                self.parse_env_only(v)
            }
        } else if let Some(d) = &self.args.default {
            self.parse_default_only(d)
        } else {
            panic!("Either env or default attribute params are required")
        };

        tokens.extend(gen);
    }
}

fn parse_attribute_args(attr: &Attribute) -> FieldArgs {
    let mut args = FieldArgs {
        env: None,
        default: None,
    };

    match attr.parse_meta().unwrap() {
        Meta::List(list) => {
            for arg in list.nested {
                if let NestedMeta::Meta(Meta::NameValue(n)) = arg {
                    let name = n.path.segments.first().unwrap().ident.to_string();
                    if name == "env" {
                        args.env = Some(n.lit);
                    } else if name == "default" {
                        args.default = Some(n.lit);
                    } else {
                        panic!("Invalid attribute argument name {}", name)
                    }
                }
            }
        }
        _ => panic!("Couldn't parse attribute arguments"),
    };

    args
}

impl From<&Field> for FieldInit {
    fn from(f: &Field) -> FieldInit {
        let args = if let Some(attr) = f.attrs.first() {
            parse_attribute_args(attr)
        } else {
            panic!("Struct fields must have the conf attribute")
        };

        FieldInit {
            name: f.ident.clone().unwrap(),
            args,
        }
    }
}

fn impl_setting_struct(name: &Ident, fields: &Punctuated<Field, Comma>) -> TokenStream {
    let init_fields: Vec<FieldInit> = fields.iter().map(|x| x.into()).collect();

    let gen = quote! {
        impl Setting for #name {
            fn init<'a>() -> Result<Self, Error<'a>> {
                Ok(Self {
                    #(#init_fields),*
                })
            }
        }
    };

    gen.into()
}

#[proc_macro_derive(Setting, attributes(conf))]
pub fn setting_derive(input: TokenStream) -> TokenStream {
    let ast: DeriveInput = syn::parse(input).unwrap();
    let name = ast.ident;
    let data = match ast.data {
        Data::Struct(d) => d,
        _ => panic!("Setting must be a struct"),
    };
    let fields = match data.fields {
        Fields::Named(FieldsNamed {
            brace_token: _,
            named,
        }) => named,
        _ => panic!("Struct fields must be named"),
    };

    impl_setting_struct(&name, &fields)
}