GHCs before 8.4 are not supported?

[qrilka]

I was trying out building some Stack packages with nix-tools but got failed. E.g. for the current Stack's master I get

error: attribute 'ghc822' missing, at /nix/store/15f66d3d57hd018sx781bvdm6cxl87q4-source/default.nix:82:21

and it looks like that line adds special patches but at https://github.com/input-output-hk/haskell.nix/tree/master/patches the oldest GHC version looks to be 8.4.1
If older versions are not supported then it makes sense to exclude corresponding Stackage snaphots as well.
Also it would be great if error from Nix were more descriptive.

[angerman]

Yes this is a bit annoying. What we do at IOHK, is to maintain our own fork of nixpkgs, and retain ghc-version in it as far back as we need. It's not optimal.

Would you think moving ghc expressions into haskell.nix was a better approach?

[qrilka]

I'm not sure I follow your last idea, which ghc expressions do you mean? One probable option I see is to make ghcHackagePatches easily overridable so if anybody wants older GHC they could create patches themselves

[ElvishJerricco]

@angerman I think it'd be good if someone made a standalone overlay for nixpkgs that defines a very large set of GHC versions.

[angerman]

@ElvishJerricco Right. That could initially live in haskell.nix as well, until we have a better place. It could also finally start reducing the copy-and-paste approach taken in nixpkgs and abstract the ghc builder int a generic one. (or even a hadrian one).

But I'm afraid that's not what @qrilka was after here I believe?

[qrilka]

@angerman it could resolve the problem I guess - if there will be some source of all the needed GHCs then there will be no special need to say explicitly that not all GHC versions (and Stackage snapshots because of that) are supported. So I think ideally it would be great to have better GHC version coverage but until there is such there is a need to document what's currently supported.

[luke-clifton]

So, #119 made it so that ghc822 which is the earliest one in nixpkgs-unstable should work now (822 being the specific example mentioned in the original comment above).

[angerman]

As we now ship our own set of compilers. And we are officially at 8.8.1 already. I'll close this for now. If someone really feels the need for those old compilers, please add them to overlays/bootstrap.nix.