"what location details should be tracked when using caller_location, either \
`none`, or a comma separated list of location details, for which \
valid options are `file`, `line`, and `column` (default: `file,line,column`)"),
- log_backtrace: Option<String> = (None, parse_opt_string, [TRACKED],
- "add a backtrace along with logging"),
ls: bool = (false, parse_bool, [UNTRACKED],
"list the symbols defined by a library crate (default: no)"),
macro_backtrace: bool = (false, parse_bool, [UNTRACKED],