dependency failure on unix library

[peterbecich]

I am attempting to use haskell-flake to build Cabal: https://github.com/peterbecich/cabal/tree/nix-flake

nix build yields

...
       > Error: Setup: Encountered missing or private dependencies:
       > unix >=2.8.6.0 && <2.9
...

The Flake uses haskell-updates branch: https://github.com/peterbecich/cabal/blob/nix-flake/flake.nix#L3
which provides unix 2.8.6.0:

nix search nixpkgs/haskell-updates#haskellPackages '^unix'
...
* legacyPackages.x86_64-linux.haskellPackages.unix_2_8_6_0 (2.8.6.0)
  POSIX functionality

Any ideas? Thanks

[roberth]

unix_2_8_6_0

A name with a version is only used in the package set when it's not the default version.
cabal2nix merely translates your cabal file and it's not aware of what is and isn't in the package set its generated expression will be loaded into.
You'll have to specify an for some package / packages to make it use that version, but it may just be a problem of the haskell-updates branch, which can be in any state of brokenness.

[peterbecich]

Thanks, that helps me understand cabal2nix better.

Understood there are no guarantees for haskell-updates.

I looked at nixpkgs/haskell-updates hackage-packages.nix and only unix_2_8_6_0 exists. Likewise on master there is a single package unix_2_8_5_1. Neither branch has unix. Can these both be set the default version? Is there any reason to not set a default version when there is only a single version?

[peterbecich]

moving discussion here https://matrix.to/#/!RbXGJhHMsnQcNIDFWN:nixos.org/$NKOaqrPbgK5OqKmthx30Gjs2zfs3rGD83R563CzcW8w?via=nixos.org&via=matrix.org&via=envs.net

[srid]

moving discussion here [..]

FYI I'm unable to access those channels due to moderator action.

Could you copy-paste what you find over there to here on GitHub discussions?

[peterbecich]

I'm sorry to hear that, you deserve to have access.
Summary is GHC boot packages only appear in haskellPackages with appended version, i.e.

* legacyPackages.x86_64-linux.haskellPackages.base_4_21_0_0 (4.21.0.0)

* legacyPackages.x86_64-linux.haskellPackages.unix_2_8_6_0 (2.8.6.0)

* legacyPackages.x86_64-linux.haskellPackages.template-haskell_2_23_0_0 (2.23.0.0)

This completely solves my confusion. My package is not building with dependencies base_4_21_0_0, unix_2_8_6_0, and template-haskell_2_23_0_0 from haskellPackages -- it is getting these dependencies directly from GHC. (I incorrectly assumed unix_2_8_6_0 was implicitly used as unix with no explicit unix in the package set.)

To determine the versions of the GHC boot packages:

$ ghc --version
The Glorious Glasgow Haskell Compilation System, version 9.10.1

$ ghc-pkg list | grep unix
   unix-2.8.5.1

And so this explains my first error:

...
       > Error: Setup: Encountered missing or private dependencies:
       > unix >=2.8.6.0 && <2.9
...

---

GHC 9.12 has the correct version of unix:

basePackages = pkgs.haskell.packages.ghc912;

However, this causes other breakages.