Unknown options are silently ignored and mixed with positional arguments

[lahwaacz]

When there are options as well as positional arguments, some of which may be optional, there is a problem with unknown options. Consider this repro case:

int foo = 0;
std::string positional;
std::string optional = "default";

auto cli = lyra::cli();
cli |= lyra::opt(foo, "foo")["--foo"];
cli |= lyra::arg(positional, "positional");
cli |= lyra::arg(optional, "optional").optional();

auto result = cli.parse(lyra::args({ argv[0], "--foo", "1", "--bar", "a" }));
if (!result) {
    std::cerr << "Error in command line: " << result.errorMessage() << std::endl;
    std::cerr << cli << std::endl;
    return EXIT_FAILURE;
}

std::cout << "foo = " << foo << std::endl;
std::cout << "positional = " << positional << std::endl;
std::cout << "optional = " << optional << std::endl;

which leads to this output:

foo = 1
positional = --bar
optional = a

This is a problem, because --bar as is not reported as unknown/invalid option, but passed to the next positional argument. It is pretty unlikely that the user intended to use --bar as a positional argument -- most likely they made a typo or another mistake and need to read the help page.

[grafikrobot]

This is related to #24

[lahwaacz]

GNU tools and many others use the -- argument as separator indicating that all following arguments are positionals rather than options. See e.g. grep example.

[grafikrobot]

GNU tools and many others use the -- argument as separator indicating that all following arguments are positionals rather than options. See e.g. grep example.

Right. There are two choices.. You do not treat "--xxx" as a special prefix that only means an option. Which is what Lyra does currently. Or you do make "--xxx" special and then need the special token, i.e. "--"by itself, to turn off the restriction. The only way for a CLI to support that would be have two different, mutually exclusive, parsing modes.

[lahwaacz]

The two choices you described are not that different/exclusive. You'd need -- even in the first case to treat a known --option as a positional argument rather than an option. Lyra currently passes only unknown/undefined options to positional arguments. E.g. if you have a --foo option and want to open a file named --foo (which is specified as a positional argument), there is no way to tell Lyra to treat --foo as positional.

[grafikrobot]

Actually there is a way to do it, or in general any form of "-- arg arg" tail options. You can specify a group with a "--" literal and a positional argument. Something like:

bool foo = false;
std::string bar;
auto c = cli() | opt(foo, "--foo") | group().sequential().add_argument(literal("--")).add_argument(arg(bar), "bar);

That's untested from memory code ;-)
It would be good to include a ready made utility to wrap that though.