Can you use a more recent cabal index than nixpkgs Haskell has?

[ParetoOptimalDev]

I think maybe you could update all-cabal-hashes and let your current version of nixpkgs use it?

Let me explain my problems and the solutions I've tried:

Problem: I needed to use a newer version of a package than nixpkgs has
Fix: Use the hackage version viahaskellProjects.default.packages = aeson.source = "newer version";.

Problem: The hackage index of nixpkgs-unstable is too old (from 8/17) to contain my package
Solution: Use the haskell-updates nixpkgs branch with inputs.nixpkgs = github:nixos/nixpkgs/haskell-updates

Problem: I get an error building my Haskell project with the haskell-updates branch
Potential Solution: Replace only the all-cabal-hashes used but use the known working nixpkgs-unstable to build my Haskell project.

That last one is what I'm asking about in the discussion title.

[srid]

Potential Solution: Replace only the all-cabal-hashes used but use the known working nixpkgs-unstable to build my Haskell project.

I'm not sure, but a good place to ask: https://app.element.io/#/room/#haskell:nixos.org

[roberth]

iiuc all-cabal-hashes is only referenced by the generation process and not by the generated code of the package set.
So it seems feasible after a bit of callHackage refactoring upstream.

[MangoIV]

perhaps another solution would be tot have a sourceDirect attribute that doesn't invoke callHackage (which uses all-cabal-hashes) but callHackageDirect

[srid]

source is already an overloaded option (can refer to either path or version). So we should reuse it? That might be overloading it a bit too much, though.

We can mitigate this confusion using URI protocols:

{
  aeson.source = "hackage-direct:1.5.0";  # With "1.5.0" being alias to "hackage:1.5.0"
}

[ParetoOptimalDev]

I would be fine with either:

• This being overloaded (though I have similar reservations)
• documenting how to use a new all-cabal-hashes

For context I run into this issue when interoperating with existing hybrid cabal/nix Haskell projects where the cabal way of things is cabal update often.

[ParetoOptimalDev]

I've found a potential solution that is using haskell-flake, calamity 😄

https://github.com/simmsb/calamity-bot/blob/54e5059fcea7c4327a2a1df77eef656b62351301/flake.nix#L47

Add all-cabal-hashes input:

all-cabal-hashes.url = "github:commercialhaskell/all-cabal-hashes/hackage";
all-cabal-hashes.flake = false;

Then use in per-system:

          basePackages = pkgs.haskell.packages.ghc944.override {
            all-cabal-hashes = inputs.all-cabal-hashes;
          };

[srid]

This would be good to document.