Function parse_options 

pub fn parse_options(
    arguments: &[OsString],
    table: &[OptionSpec],
    mode: ParseMode,
    wrapper_flags: &[&[u8]],
) -> Result<ParsedOptions, OptionError>

What: Tokenize one region in a single forward pass (parse_options_step, parse-options.c:995-1169). Result<A, B> is “either success A or failure B”. Why: One faithful scan replaces per-command guesses about option arity. Gotcha: Indexes in the result are relative to arguments, the region after the subcommand.

In TS you’d write (pseudocode):

function parseOptions({ args, table, mode, wrapperFlags }): ParsedOptions; // throws OptionError