pub fn contains_package(&self, package_id: &PackageId) -> Result<bool, Error> {
        let package = self.graph.package_graph.metadata(package_id)?;
        Ok(self
            .graph
            .feature_ixs_for_package_ix(package.package_ix())
            .any(|feature_ix| self.core.contains(feature_ix)))
    }
Returns true if this set contains this package.

Returns an error if this package ID was unknown.
guppy/src/graph/feature/resolve.rs