if ext_str.chars().skip(1).all(|c| c.is_uppercase() || c.is_ascii_digit())
|| ext_str.chars().skip(1).all(|c| c.is_lowercase() || c.is_ascii_digit());
let recv_ty = cx.typeck_results().expr_ty(recv).peel_refs();
if ext_str.chars().skip(1).all(|c| c.is_uppercase() || c.is_ascii_digit())
|| ext_str.chars().skip(1).all(|c| c.is_lowercase() || c.is_ascii_digit());
let recv_ty = cx.typeck_results().expr_ty(recv).peel_refs();