I think that sums it up nicely. To add to that: Spack's solver effectively generates these 'concrete' packages for you. In the example, suppose you're packagi

I think that sums it up nicely. To add to that: Spack's solver effectively generates these 'concrete' packages for you. In the example, suppose you're packaging `X`, it depends on already existing packages `A` and `B`, and `A` needs `curl +foo` and `B` needs `curl +bar`; then Spack is convenient as you don't have to worry about the transitive dependency curl, the solver will output `curl +foo +bar`. That should make contributing to Spack potentially easier, cause you just have to define X, the solver will figure out the flavor of transitive dependencies, and there's no need to create the `curl-with-foo-and-bar` package (and you don't have to modify `A` and `B` to use `curl-with-foo-and-bar` either)