extern crate proc_macro;
use proc_macro::TokenStream;
use proc_macro2::{Ident, TokenStream as TokenStream2};
use quote::quote;
use syn::{parse_macro_input, Data, DeriveInput, Field, Fields, LitStr};
#[proc_macro_derive(LoadEnv, attributes(econf))]
pub fn load_env(input: TokenStream) -> TokenStream {
let input = parse_macro_input!(input as DeriveInput);
let name = input.ident;
let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();
let content = content(&name, &input.data);
let expanded = quote! {
impl #impl_generics ::econf::LoadEnv for #name #ty_generics #where_clause {
fn load(self, path: &str, loader: &mut ::econf::Loader) -> Self {
#content
}
}
};
TokenStream::from(expanded)
}
fn is_skip(f: &Field) -> bool {
f.attrs.iter().any(|attr| {
if attr.path().is_ident("econf") {
if let Ok(args) = attr.parse_args::<Ident>() {
return args == "skip";
}
}
false
})
}
fn find_renaming(f: &Field) -> Option<String> {
let mut rename = None;
for attr in &f.attrs {
if attr.path().is_ident("econf") {
attr.parse_nested_meta(|meta| {
if meta.path.is_ident("rename") {
let s: LitStr = meta.value()?.parse()?;
rename = Some(s.value());
}
Ok(())
})
.expect("failed to parse nested meta");
}
}
rename
}
fn content(name: &Ident, data: &Data) -> TokenStream2 {
match data {
Data::Struct(data) => match &data.fields {
Fields::Named(fields) => {
let fields = fields.named.iter().map(|f| {
let ident = &f.ident;
if is_skip(f) {
return quote! {
#ident: self.#ident,
};
}
match find_renaming(f) {
Some(overwritten_name) => quote! {
#ident: self.#ident.load(&(path.to_owned() + "_" + #overwritten_name), loader),
},
None => quote! {
#ident: self.#ident.load(&(path.to_owned() + "_" + stringify!(#ident)), loader),
}
}
});
quote! {
Self { #(
#fields
)* }
}
}
Fields::Unnamed(fields) => {
let fields = fields.unnamed.iter().enumerate().map(|(i, f)| {
let i = syn::Index::from(i);
let i = &i;
if is_skip(f) {
return quote! { self.#i, };
}
match find_renaming(f) {
Some(overwritten_name) => quote! {
self.#i.load(&(path.to_owned() + "_" + #overwritten_name), loader),
},
None => quote! {
self.#i.load(&(path.to_owned() + "_" + &#i.to_string()), loader),
},
}
});
quote! {
Self ( #(
#fields
)* )
}
}
Fields::Unit => quote!(#name),
},
Data::Enum(data) => {
data.variants.iter().for_each(|f| match f.fields {
Fields::Named(_) => panic!("Enum variant with named fields are not supported"),
Fields::Unnamed(_) => panic!("Enum variant with unnamed fields are not supported"),
Fields::Unit => {}
});
quote! {
loader.load_from_str(self, path)
}
}
Data::Union(_) => unimplemented!("Unions are not supported"),
}
}