Can't build cabal from sources.

[typetetris]

Steps to reproduce

1. git clone https://github.com/haskell/cabal.git
2. cd cabal
3. git branch v32 cabal-install-v3.2.0.0
4. git checkout v32
5. create default.nix with the folloging content

let 
  # Fetch the latest haskell.nix and import its default.nix 
  haskellNix = import (builtins.fetchTarball https://github.com/input-output-hk/haskell.nix/archive/master.tar.gz) {};
  # haskell.nix provides access to the nixpkgs pins which are used by our CI, hence
  # you will be more likely to get cache hits when using these. 
  # But you can also just use your own, e.g. '<nixpkgs>'
  nixpkgsSrc = haskellNix.sources.nixpkgs-1909;
  # haskell.nix provides some arguments to be passed to nixpkgs, including some patches
  # and also the haskell.nix functionality itself as an overlay.
  nixpkgsArgs = haskellNix.nixpkgsArgs;
in
{ pkgs ? import nixpkgsSrc nixpkgsArgs
, haskellCompiler ? "ghc865"
}:
# 'cabalProject' generates a package set based on a cabal.project (and the corresponding .cabal files)
pkgs.haskell-nix.cabalProject {
  # 'cleanGit' cleans a source directory based on the files known by git
  src = pkgs.haskell-nix.haskellLib.cleanGit { src = ./.; };
  ghc = pkgs.buildPackages.pkgs.haskell-nix.compiler.${haskellCompiler};
}

6. nix build -f default.nix cabal-install.components.exes.cabal
7. See it fail.

Additional Info

Trying to look around in the resulting derivation with

 nix repl default.nix

and using tab completion, shows, there is a Cabal key, but it has a null value.

Also entering the shell with

nix-shell -A shellFor default.nix

and using

ghc-pkg list

shows, that the only Cabal the library package known to the compiler in the shell is the one
it brings with it. (At the time of writing: Cabal-2.4.0.1)

[hamishmack]

Try:

pkgs.haskell-nix.cabalProject {
  # 'cleanGit' cleans a source directory based on the files known by git
  src = pkgs.haskell-nix.haskellLib.cleanGit { src = ./.; };
  ghc = pkgs.buildPackages.pkgs.haskell-nix.compiler.${haskellCompiler};
  modules = [ { reinstallableLibGhc = true; } ];
}

The reinstallableLibGhc = true will tell cabalProject that it is ok not to use the Cabal that came with ghc and instead install a new one if necessary (in this case it should install the one from the project itself).

[KiaraGrouwstra]

Did this solution work for you @typetetris? I've been having trouble with it.

edit: this went thru for me now. :)

[hamishmack]

reinstallableLibGhc is now the default