How do I find out what "buildRustPackage" has as far as options? Like, I see it has a 'buildFeatures' option by looking at someone else's code, but does it have a buildPackages option, for instance? Where would I look to find that out?

Basically I want to specify which particular binary in the cargo.toml to build. Normally would do this with cargo build --package mybin but not sure how in the buildRustPackage helper.