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use proc_macro::TokenStream;
use quote::{ToTokens, quote};
use syn::{Data, DeriveInput, Fields, parse_macro_input};
#[proc_macro_derive(FromArgs)]
pub fn derive_cli(input: TokenStream) -> TokenStream {
let input = parse_macro_input!(input as DeriveInput);
let name = input.ident;
let fields = match input.data {
Data::Struct(data) => data.fields,
_ => panic!("Cli can only be derived for structs"),
};
let mut field_parsers_init = Vec::new();
let mut field_parsers = Vec::new();
let mut field_parsers_post = Vec::new();
let mut field_names = Vec::new();
if let Fields::Named(fields_named) = fields {
for field in fields_named.named {
let ident = field.ident.unwrap();
let name_str = ident.to_string();
let mut long_name = b"--".to_vec();
long_name.extend_from_slice(name_str.as_bytes());
let long_name = proc_macro2::Literal::byte_string(&long_name);
field_names.push(ident.clone());
// initialization
field_parsers_init.push(quote! {
let mut #ident = None;
});
let is_bool = field.ty.to_token_stream().to_string() == String::from("bool");
let is_option = field.ty.to_token_stream().to_string().starts_with("Option"); // bad bad detection
// in the loop
if is_bool {
field_parsers.push(quote! {
if arg == #long_name {
#ident = Some(true);
continue;
}
});
} else {
field_parsers.push(quote! {
if arg == #long_name {
let Some(val) = iter.next() else {
return Err(ArgParseError::MissingArgValue(#name_str));
};
match String::from_utf8_lossy(val).parse() {
Ok(parsed) => {
#ident = Some(parsed);
continue;
}
Err(err) => {
return Err(ArgParseError::ArgValueParseError(#name_str, format!("{err:?}")));
}
}
}
});
}
// after loop
if is_bool {
field_parsers_post.push(quote! { let #ident = #ident.unwrap_or(false); });
} else if !is_option {
field_parsers_post.push(quote!{ let Some(#ident) = #ident else { return Err(ArgParseError::MissingArg(#name_str)) }; });
}
}
}
let expanded = quote! {
impl ArgParse for #name {
fn parse<'a>(args: &'a [BString]) -> std::result::Result<Self, ArgParseError<'a>> {
let mut iter = args.iter();
#(#field_parsers_init)*
while let Some(arg) = iter.next() {
#(#field_parsers)*;
return Err(ArgParseError::LeftoverArg(arg));
}
#(#field_parsers_post)*
Ok(Self { #( #field_names ),* })
}
}
};
TokenStream::from(expanded)
}
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