Nix & Haskell - using default.nix from cabal2nix and a generic shell.nix - haskell

Question

From a pretty basic cabal file
cabal2nix ./. > default.nix
and then a shell.nix of
let
pkgs = import <nixpkgs> {};
haskellPackages = pkgs.haskellPackages_ghc784.override {
extension = self: super: {
thispackage = self.callPackage ./default.nix {};
};
};
in pkgs.myEnvFun {
name = haskellPackages.thispackage.name;
buildInputs = [
(haskellPackages.ghcWithPackages (hs: ([
hs.cabalInstall
] ++ hs.thispackage.propagatedNativeBuildInputs)))
];
}
When in the nix-shell and running cabal configure it complains of missing packages such as text.
If I put the text package explicitly into the shell.nix such as
let
pkgs = import <nixpkgs> {};
haskellPackages = pkgs.haskellPackages_ghc784.override {
extension = self: super: {
thispackage = self.callPackage ./default.nix {};
};
};
in pkgs.myEnvFun {
name = haskellPackages.thispackage.name;
buildInputs = [
(haskellPackages.ghcWithPackages (hs: ([
hs.cabalInstall
hs.text
] ++ hs.thispackage.propagatedNativeBuildInputs)))
];
}
The cabal configure is fine, but I would expect hs.thispackage.propagatedNativeBuildInputs to be supplying these packages.
The very basic haskell project can be seen at
https://github.com/fatlazycat/haskell-nix-helloworld
Am I wrong in assuming you can work in this way ?
Thanks

Answer 1

The propagatedNativeBuildInputs attribute is used by Haskell libraries to
propagate their build inputs down to other builds that depend on them. Your
package, however, is not a library --- it's an executable ---, so there's no
need to propagate the build inputs and thus propagatedNativeBuildInputs is
empty. Instead, you'll find the information you need in
hs.thispackage.extraBuildInputs.
Generally speaking, the definition of these kind of nix-shell environments
has become a lot easier in the release-15.09 branch (or nixos-unstable),
though. Simply run cabal2nix --shell . >shell.nix and you get a shell.nix
file that you can use for building with nix-build shell.nix as well as for
entering an interactive development environment with nix-shell.
http://nixos.org/nixpkgs/manual/#users-guide-to-the-haskell-infrastructure has
a lot more information about the subject.