fn expand_derive_macro(
invoc_id: LocalExpnId,
input: TokenStream,
ecx: &mut ExtCtxt<'_>,
client: Client<TokenStream, TokenStream>,
) -> Result<TokenStream, ()>fn expand_derive_macro(
invoc_id: LocalExpnId,
input: TokenStream,
ecx: &mut ExtCtxt<'_>,
client: Client<TokenStream, TokenStream>,
) -> Result<TokenStream, ()>