{"ast_node_type":"function","tokens":[{"end":82,"kind":"keyword","start":0,"text":"fn"}]}
    fn check_field_decl(&mut self, field_name: Ident, field_decl: FieldDeclSpan) {
    /// Check if a given field `ident` declared at `field_decl` has been declared elsewhere before.
        use FieldDeclSpan::*;