callCabal2nix default.nix is garbage collected

[ElvishJerricco]

When using callCabal2nix, the resulting derivation has no gc link to the IFD'd default.nix. I think this should be added as a build time dependency so that cabal2nix doesn't get collected, and so you don't have to repeatedly wait for the derivation to be built. It's minor, but enough to be annoying.

[ElvishJerricco]

/cc @shlevy @peti

[shlevy]

👍 from me.

[peti]

I'm not sure whether I understand this correctly. You want to prevent the garbage collector from collecting a file that it could collect so that this file doesn't have to be re-built even though it can be re-built?

[shlevy]

@peti It would only be a build-time dependency, and thus only kept if keep-derivations and keep-outputs are both true. Those settings indicate "I don't want to have to do any work to rebuild things I already have and I'll take the disk hit"

[peti]

Hmm, okay. That sounds fine.

[ncfavier]

Just pointing out that #36216 was reverted by #194753 to avoid rebuilds, but you can still explicitly add a GC root on haskellPackages.foo.cabal2nixDeriver.