suggestion: Adding extra packages to shell

[turboMaCk]

Hello 👋

I've personally found it helpful to have the ability of adding some extra dev tools dependencies to nix-shell. I'm not really sure if this the best way to do it but it was not obvious for me at first how to do it and this is what I came up with.

Given this repository is under your name feel free to close this PR if this is not something you would personally feel is wise to recommend. No preasure.

[anka-213]

@Gabriel439 How would you make such a shell attribute in release.nix? You would have to combine the env with the extra packages somehow, but I can't quite figure out the specifics.

[Gabriella439]

@anka-213: I believe you can do this with the pkgs.lib.mkShell utility (https://github.com/NixOS/nixpkgs/blob/300c205cf9bfd86f65dabcc1f3b4439cea42cbc1/pkgs/build-support/mkshell/default.nix), like this:

pkgs.lib.mkShell {
  inputsFrom = [ pkgs.haskellPackages.myPackage.env ];

  builtInputs = [ pkgs.myExtraTool ];
}

[anka-213]

@Gabriel439 I'm afraid I celebrated too early. That does not seem to work. The shell no longer contains the dependencies for myPackage with this shell.

[turboMaCk]

@anka-213 what about something like:

rec {
  project = ....;
  shell = project.env // pkgs.mkShell {
    buildInputs = [ pkgs.myExtraTool ];
  };
}

nix-shell -A shell

Also, I would maybe try to remove .env from inputsFrom but I'm not sure if that should help or not.

[anka-213]

@turboMaCk That unfortunately seems to work even worse. Now we are even missing ghc, not just the haskell libraries that we depended on.

[turboMaCk]

I think what I end up doing is to run nix-build before nix-shell when some dependencies are changed which I think resolved similar issues for me. I know it seems like a workaround but you can try it. It might also provide some hints of what is going wrong...

[anka-213]

@turboMaCk It didn't help and I can't see how it would? nix-build is supposed to have no side-effects.

However, I believe that the function shellFor could be used successfully. Here's an example of it being used: https://github.com/Infinisil/soph/blob/master/shell.nix

[turboMaCk]

Shouldn't but given derivations are evaluated lazily and bugs do exist... I don't know nix internals enough to guess really. Pls, let us know if you're successful with shellFor .

[Gabriella439]

Also, my instructions could have been wrong. I didn't test them first 🙂

[Gabriella439]

@anka-213: So I just tested this and as far as I can tell the example I gave should work (except replacing pkgs.lib.mkShell with pkgs.mkShell and builtInputs with buildInputs):

pkgs.mkShell {
  inputsFrom = [ pkgs.haskellPackages.myPackage.env ];

  buildInputs = [ pkgs.myExtraTool ];
}

How are you verifying that it doesn't work?

[Boshen]

So shell.nix becomes

{ pkgs ? import <nixpkgs> { } }:
let
  project = pkgs.haskellPackages.callPackage ./project0.nix { };
in pkgs.mkShell {
  buildInputs = [ pkgs.haskellPackages.ghcid ];
  inputsFrom = [ project.env ];
}

I've created a repo if anyone wants to try this out: https://github.com/Boshen/nix-haskell