pub fn member_ids(&self) -> impl Iterator<Item = &'g PackageId> + ExactSizeIterator {
        self.inner.members_by_path.iter().map(|(_path, id)| id)
    }
Returns an iterator over package IDs for workspace members. The package IDs will be returned
in the same order as `members`, sorted by the path they're in.
guppy/src/graph/graph_impl.rs