Bump haskellPackages to GHC-9.4, LTS-21 in Nixpkgs

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The Haskell team in Nixpkgs is in the process of bumping haskellPackages to LTS-21, GHC-9.4. We’d love to get help from any Haskell users with fixing broken Haskell packages!

https://github.com/NixOS/nixpkgs/pull/240387

We plan on merging this PR to master in two to three weeks (but we haven’t decided on the exact date), and marking all un-buildable Haskell packages as broken. If any of your packages currently are broken on Hydra on the haskell-updates branch, we’d appreciate PRs fixing them and/or new releases pushed to Hackage. If you need help fixing your packages, feel free to reach out to us on GitHub, Discourse, or Matrix .

This bump has caused some (expected) breakage, so we’d appreciate help fixing some of these packages!

Here’s a few helpful links:

  • The daily haskell-updates build reports are a good place to see if any of your maintained packages are not buildable by Hydra, or even just get an overview of the packages to focus on fixing.
  • You can find open Haskell-related PRs in the Nixpkgs repo with the haskell label.
  • We have a new and improved Haskell section in the Nixpkgs manual. If you find have any questions about how the Haskell infrastructure works in Nixpkgs, you may want to take a look at the manual. If you have any questions that aren’t answered in the manual, feel free to ask on GitHub, Discourse, or Matrix .
  • The previous bump to LTS-20, GHC-9.2: Bump `haskellPackages` to GHC-9.2, LTS-20 in Nixpkgs
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I’ve merged the PR now. Unfortunately, it seems to me that while GHC 9.4 did not break too much, the transition from Stackage LTS 20 to 21 was a difficult one (with other contributing factors). If you have a non trivial Haskell project using nixpkgs, you will likely experience some regressions. We’ll do our best to sort those out in the coming weeks. Feel free to open issues for things you care about!

You can get an overview of newly broken packages here.

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