Nix derivation to install clever-tools - see https://github.com/CleverCloud/clever-tools
First, edit clever-tools/default.nix, to update the version number. For the expected hash, you can put 0000000000000000000000000000000000000000000000000000 (52 zeroes).
Then, edit default.nix, update the callPackage line to the new version, as well as the latest value.
Once you've done that, add a mkOlderVersion for the previous latest version. Once again, you can use the null hash for sha256.
Then, run nix build. It will give you the correct values for the hashes. Correct those, run it again and you'll see result- directories, one per version. Go ahead and make sure they all work.
Finally, don't forget to update scripts/check.sh with the latest version number.