I'm looking to create a packages.yaml file specific to CentOS-7. I noticed that Spack provides platform-specific scopes. But when I looked at it, it seems that the scope is specific to just linux, not linux-centos7-x86_64, which is what I'm running.

I want an OS-specific scope so I can add things specific to my Linux distro; mostly, directing it to use system-supplied libraries for various packages that I don't want to build (on my system). For example:

   qt:
        paths:
            qt@4.8.5: /
        version: [4.8.5]
        buildable: False

    libxaw:
        paths:
            libxaw@1.0.12: /
        version: [1.0.12]
        buildable: False

Might I suggest a further expansion of scopes, to provide for OS-specific as well as platform-specific scopes? Now the default hierarchy would look like this on my system:

1. defaults
2. defaults/linux
3. defaults/linux-centos7-x86_64
4. site
5. site/linux
6. site/linux-centos7-x86_64
7. user
8. user/linux
9. user/linux-centos7-x86_64