Motivation for this change

HPC environments are slowly moving forward, hence it would be very nice to support multiple versions of Singularity.

I have tried my best, following similar patterns for nginx and boost packages, but not yet succeeded at making this build. I need help, moving forward on this.

I get the following error:

error: attempt to call something which is not a function but a set, at /home/obiwan/stash/sources/scalavision/nixpkgs/pkgs/applications/virtualization/singularity/singularity_3_0_1.nix:3:28

How can I rearrange this to make it work?

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nix-review --run "nix-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Assured whether relevant documentation is up to date
• Fits CONTRIBUTING.md.