@ElvishJerricco what should I do when I do want to rebuild anytime I change the rev in

          package_latest = hsuper.callCabal2nix "language-puppet" (pkgs.fetchFromGitHub {
            owner  = "xxxxx";    repo   = "language-puppet";
            rev = "2845454bd0bc95771d875df273adc63e24ddaded";
            sha256 = "1iz5gflicris9jf5fvzfv8i69hmsr432dbv4hrpvqk0z1sqh0qbb";
          }) { };

This is actually quite a common workflow for me right now. I want to get the latest revision of a package in github but the cabal file is left unchanged because it is not released yet.

Is there an easy way to do that without removing the cached derivation ?

@PierreR That should work given this change no problem. Notice that it overrides the src field to put back the src argument; if that src is different, it will yield a different derivation, even if the cabal file is unchanged.

@ElvishJerricco I am using nix-shell -A project release.nix with release.nix

I was using a simple version of this before with an older pinned nixpkgs version and it did refresh. If you don't see anything that is obviously wrong in 'release.nix' I will check that with older version to be sure.

Thanks for your quick feedback.

@PierreR fetchFromGitHub is a fixed output derivation. If you don't change the sha256 argument, then any changes to the other arguments will not trigger a rebuild, even if such a rebuild would fail since the src hash is wrong. Notice that your nixpaste link contains a fetchFromGitHub expression that does not build. To test this, you can use --check, like nix-build release.nix -A language-puppet_latest.src --check, if you add language-puppet_latest to the release.nix output. The reason that you did not notice this is that you kept the sha256 from a different version that you had successfully built, which told Nix not to retry the src download, and just use the old one.

I think fetchFromGitHub used to not exhibit this behavior, and would get treated as a different derivation if only the rev changed and not the sha (which would fail), so that might be why this used to work for you.

TL;DR: This is fetchFromGitHub's fault, not callCabal2nix's. You need to update your sha256.

The typical hack is to make some random change in the hash.

@ElvishJerricco I wasn't aware about the change. Thanks for your valuable help !