Use hpack to generate cabal files when required

[qrilka]

Corresponding PR in nix-tools is input-output-hk/nix-tools#40

[angerman]

As mentioned in input-output-hk/nix-tools#40, I'd rather see this done in haskell.nix.

If we add

  inherit (config) hsPkgs;

to

haskell.nix/modules/component-driver.nix

Lines 4 to 10 in 0b2d033

	new-builder = haskellLib.weakCallPackage pkgs ../builder {
	inherit haskellLib;
	ghc = config.ghc.package;
	buildGHC = buildModules.config.ghc.package;
	inherit (config) nonReinstallablePkgs;
	inherit withPackage;
	};

Threading it through:

haskell.nix/builder/default.nix

Line 1 in 0b2d033

{ pkgs, buildPackages, stdenv, lib, haskellLib, ghc, buildGHC, fetchurl, writeText, runCommand, pkgconfig, nonReinstallablePkgs, withPackage }:

and

haskell.nix/builder/default.nix

Line 74 in 0b2d033

comp-builder = haskellLib.weakCallPackage pkgs ./comp-builder.nix { inherit ghc haskellLib nonReinstallablePkgs withPackage; };

I would hope that adding hsPkgs in

haskell.nix/builder/comp-builder.nix

Line 1 in 0b2d033

{ stdenv, buildPackages, ghc, lib, pkgconfig, writeText, runCommand, haskellLib, nonReinstallablePkgs, withPackage }:

would then allow using it hsPkgs.buildPackages.hpack in the builder?

[ElvishJerricco]

Agreed. nix-tools should not be making assumptions about where to get the cabal-generator from. This task should be 100% haskell.nix