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extern crate proc_macro;
use proc_macro::TokenStream;
use proc_macro2::TokenTree;
use quote::quote;
use syn::{parse_macro_input, Data, DataEnum, DeriveInput, Ident, Variant};
#[derive(Clone)]
struct EnvOptVariant {
ident: Ident,
name: String,
default: Option<String>,
}
#[proc_macro_derive(EnvOpt, attributes(envopt))]
pub fn derive(input: TokenStream) -> TokenStream {
let ast = parse_macro_input!(input as DeriveInput);
let enum_name = ast.ident;
if let Data::Enum(DataEnum { variants, .. }) = ast.data {
let envopt_variants: Vec<_> = variants
.into_iter()
.map(|variant| {
let ident = variant.ident.clone();
let name = get_name_attr(&variant).expect("No name found");
let default = get_default_attr(&variant);
EnvOptVariant {
ident,
name,
default,
}
})
.collect();
let validate_matches: Vec<_> = envopt_variants
.clone()
.into_iter()
.filter_map(|variant| {
let name = variant.name;
if variant.default.is_none() {
Some(quote! {
match std::env::var(#name) {
Ok(_) => {}
Err(_) => {
errors.push(concat!("Environment variable ", stringify!(#name), " not set").into());
}
}
})
} else {
None
}
})
.collect();
let value_matches: Vec<_> = envopt_variants
.into_iter()
.map(|variant| {
let ident = variant.ident;
let name = variant.name;
match variant.default {
Some(default) => quote! {
#enum_name::#ident => match std::env::var(#name) {
Ok(val) => Ok(val),
Err(_) => Ok(#default.into()),
}
},
None => quote! {
#enum_name::#ident => match std::env::var(#name) {
Ok(val) => Ok(val),
Err(_) => Err(concat!("Environment variable ", stringify!(#name), " not set").into()),
}
},
}
})
.collect();
let impl_env_opt = quote! {
impl envopt::EnvOpt for #enum_name {
fn validate() -> Result<(), Vec<String>> {
let mut errors = Vec::new();
#(#validate_matches)*
if errors.is_empty() {
Ok(())
} else {
Err(errors)
}
}
fn value(&self) -> Result<String, String> {
match self {
#(#value_matches),*
}
}
}
};
TokenStream::from(impl_env_opt)
} else {
TokenStream::new()
}
}
fn get_attr(name: String, variant: &Variant) -> Option<String> {
for attr in variant.attrs.clone() {
if attr.path.segments.first().unwrap().ident == "envopt" {
for token in attr.tokens {
if let TokenTree::Group(group) = token.clone() {
let mut token_stream_iter = group.stream().into_iter();
while let Some(x) = token_stream_iter.next() {
if let TokenTree::Ident(i) = x {
if &i == &Ident::new(&name, i.span().clone()) {
token_stream_iter.next();
let mut s = token_stream_iter.next().unwrap().to_string();
s.remove(0);
s.pop();
return Some(s);
}
}
}
}
}
}
}
None
}
fn get_name_attr(variant: &Variant) -> Option<String> {
dbg!(get_attr("name".into(), variant))
}
fn get_default_attr(variant: &Variant) -> Option<String> {
dbg!(get_attr("default".into(), variant))
}
#[cfg(test)]
mod test {
#[test]
pub fn test() {}
}