Cabal file

[mulderr]

Hi again,

first of thank you for the latest changes! However, if I can nitpick a bit more, please keep the cabal file in the project. Among other things it's used by Nix tools to automatically create expressions. Removing it means odpic-raw will be broken on NixOS.

BTW. since odpic is now in nixpkgs, on master you can get a working shell with odpic-raw using:

nix run '(import <nixpkgs> {}).haskellPackages.ghcWithPackages(ps: [ ps.odpic-raw ])'

[mulderr]

Ah, I think cabal2nix may be handling this automatically these days. Not sure though. Will verify later today.

[mulderr]

After examining this closer, if that's ok, I would suggest keeping the hpack generated cabal file in the repo. As does hpack itself.

Otherwise the build depends on the version of hpack the user has available on the build system. This is not great for Nix and it's reproducible builds. Especially that package.yaml does not specify the minimal version of hpack to be used.

Depending on how I run hpack on my machine it will either fail altogether or ignore the defaults field because NixOS 18.03 currently has 0.21.2 and support for local files in defaults was added in 0.26.

[leptonyu]

Hi, I don't use nix, so I'm not sure the compatible of nix and hpack. How about to change defaults as follows?

  github: leptonyu/odpic-raw
  ref: master
  path: defaults.yaml

[leptonyu]

Another solution may be that I can keep the odpic-raw.cabal file in the project.

[mulderr]

I'd vote for keeping the generated cabal file in the project.

This time we can fix things by using a different value for defaults but that may not always be the case. Also, does hackage automatically handle hpack? Don't you need to generate the file anyway before you upload? Even if it does handle hpack automatically than I guess my previous point stands - it's not reliable because it may be using a different version of hpack than you intended.

[leptonyu]

Hackage do not known exists of hpack, only odpic-raw.cabal will upload to hackage. I can build succeed by stack --nix build locally.

so nix use which source to build odpic-raw? hackage source or github?

[leptonyu]

odpic-raw hackage source

[mulderr]

Nix will normally use the version on hackage. Which specific one depends on the version of nixpkgs. List of hackage packages for Nix is generated from an LTS snapshot AFAIK. But nix does not use stack. It needs a .cabal file one way or another to generate the expression.

However, it's very nice to be able to override that and point it to github when you're working on something or need a newer version than is in the nixpkgs you're using. Also a lot of people like to pin dependencies in their projects to specific commits on github. In that case cabal2nix may try to run hpack if it does not find .cabal but there is no guarantee it will use a correct version of hpack and that can cause problems.

[leptonyu]

@mulderr ok, let's keep the .cabal file.

[leptonyu]

@mulderr how to publish a haskell package to nix? Do I have to trigger something?

[mulderr]

Thanks again for a quick solution!

Re nix, the only thing you need to do as a package maintainer is to upload to hackage. The rest happens automatically or is taken care of by nixpkgs contributors.

There is usually some delay until a package uploaded to hackage appears in nixpkgs. For example as of right now the version in nixpkgs is still 0.2.1 and hackage already has 0.3.0. But it should soon be updated. Commit history suggets it's updated every couple days at least.