{"ast_node_type":"variable","tokens":[{"end":86,"kind":"keyword","start":0,"text":"let"}]}
    let field = file.syntax().descendants().find_map(ast::RecordField::cast).unwrap();
    let file = SourceFile::parse("struct Foo { f: u32, }", parser::Edition::CURRENT).ok().unwrap();
    let ptr = SyntaxNodePtr::new(field.syntax());