haskellPackages.cabal2nix-unstable: override with unstable dependencies

These dependencies need to be pulled from the same unstable commit that
cabal2nix is pulled from, otherwise changes to any of them will not be
in effect and possibly break the build.

maintainers/scripts/haskell/update-cabal2nix-unstable.sh

@@ -12,8 +12,16 @@ head_info="$(curl -H "Accept: application/vnd.github.v3+json" https://api.github
 commit="$(jq -r .commit.sha <<< "$head_info")"
 # extract commit timestamp and convert to date
 date="$(date "--date=$(jq -r .commit.commit.committer.date <<< "$head_info")" +%F)"
+
 # generate nix expression from cabal file, replacing the version with the commit date
-output=pkgs/development/haskell-modules/cabal2nix-unstable.nix
-echo '# This file defines cabal2nix-unstable, used by maintainers/scripts/haskell/regenerate-hackage-packages.sh.' > "$output"
-cabal2nix --subpath cabal2nix "https://github.com/NixOS/cabal2nix/archive/$commit.tar.gz" | sed -Ee 's/version = "(.*)"/version = "\1-unstable-'"$date"'"/' >> "$output"
-nixfmt "$output"
+function mkPackage() {
+  output=pkgs/development/haskell-modules/cabal2nix-unstable/$1.nix
+  echo "# This file defines $1-unstable, used by maintainers/scripts/haskell/regenerate-hackage-packages.sh." > "$output"
+  cabal2nix --subpath "$1" "https://github.com/NixOS/cabal2nix/archive/$commit.tar.gz" | sed -Ee 's/version = "(.*)"/version = "\1-unstable-'"$date"'"/' >> "$output"
+  nixfmt "$output"
+}
+
+mkPackage "cabal2nix"
+mkPackage "distribution-nixpkgs"
+mkPackage "hackage-db"
+mkPackage "language-nix"