Cabal 3.12

[mniip]

We're currently experiencing a combination of unfortunate circumstances:

• We have packages with build-type: Custom in our dependency closure, meaning they depend on setup.Cabal.
• cabal --enable-multi-repl requires setup.Cabal >= 3.12.
• cabal freeze writes a freeze file that includes setup.* dependencies, so having a freeze file staged under git requires committing to a single choice of a setup.Cabal version.
• haskell.nix uses nix-tools compiled against Cabal 3.10.3.0
• Cabal 3.10's planner requires setup.Cabal < 3.12 in the plan: Does cabal-3.10 impose setup.Cabal < 3.12? haskell/cabal#9917
• I couldn't figure out how to make haskell.nix use a differently compiled nix-tools.
• nix-tools does not support Cabal 3.12 anyway
  

  haskell.nix/nix-tools/nix-tools/nix-tools.cabal

  Lines 18 to 19 in 8d879c1

  	Cabal ^>=3.12,
  	Cabal-syntax ^>=3.12

Would it be possible to migrate nix-tools to Cabal 3.12, or otherwise lift the restriction and have a way for me to override the Cabal version used in nix-tools?

[mniip]

Looks like nix-tools does work with 3.12 actually. There's an allow-newer in its cabal.project:

haskell.nix/nix-tools/cabal.project

Lines 12 to 15 in 8d879c1

	allow-newer:
	algebraic-graphs:deepseq,
	hackage-db:base,
	hackage-db:Cabal,

and it builds just fine.

I am able to work around this issue by overriding nix-tools for a specific project like so:

pkgs.haskell-nix.cabalProject {
  inherit compiler-nix-name;
  src = ...;
  nix-tools = pkgs.haskell-nix.nix-tools-set {
    inherit compiler-nix-name; # Don't build a new GHC (9.10.1) just for this
    cabalProjectLocal = ''
      constraints:
        Cabal ==3.12.1.0
    '';
};

cabalProjectLocal is not the prettiest, there's probably some better way to do this via modules. And also a better way to override this for the entire pkgs rather than just a single project. (I couldn't figure out how to do either).