haskellPackages.callCabal2nix: provide fallback name

[3noch]

@peti I realized just after my last patch that callCabal2nix did not accept paths (e.g. callCabal2nix ./. {} is an error). This is too limiting. Sorry I didn't catch it earlier.

Do you have any other recommendations while I'm revisiting this?

[mention-bot]

@3noch, thanks for your PR! By analyzing the history of the files in this pull request, we identified @peti, @oxij and @aske to be potential reviewers.

[k0001]

I just came across this issue myself. I agree with @3noch's proposed patch here.

[k0001]

Hmm.. this doesn't quite work for me. When src a /nix/store/ path (like when calling callCabal2nix on "pkgs.fetchFromGitHub {...} + "/tools", then this fails with an error like:

while evaluating the derivation attribute ‘name’ at /home/k/q/nixpkgs.git/pkgs/development/haskell-modules/default.nix:64:13:
the string ‘cabal2nix-tools’ is not allowed to refer to a store path (such as ‘!out!/nix/store/8ddkgk5wfxycarz4aqliyn2glrhmmnjd-gtk2hs-eee61d84edf1dd44f8d380d7d7cae2405de50124-src.drv’), at /nix/store/jj3kq2dmllvkqwwbhnmzbk9hfgncdbvl-nix-1.11.6/share/nix/corepkgs/derivation.nix:8:12

[k0001]

You can reproduce the error with this:

let
pkgs = import <nixpkgs> {};
src = pkgs.fetchFromGitHub {
  owner = "gtk2hs";
  repo = "gtk2hs";
  rev = "eee61d84edf1dd44f8d380d7d7cae2405de50124";
  sha256 = "12i53grimni0dyjqjydl120z5amcn668w4pfhl8dxscjh4a0l5nb";
};
in pkgs.haskellPackages.callCabal2nix "${src}/tools" {}

[peti]

How do you folks like #22469? That is gonna work for sure.