borrowck: Option<String> = (None, parse_opt_string, [UNTRACKED],
"select which borrowck is used (`ast`, `mir`, `migrate`, or `compare`)"),
two_phase_borrows: bool = (false, parse_bool, [UNTRACKED],
borrowck: Option<String> = (None, parse_opt_string, [UNTRACKED],
"select which borrowck is used (`ast`, `mir`, `migrate`, or `compare`)"),
two_phase_borrows: bool = (false, parse_bool, [UNTRACKED],