IOHK Common Nix Code

This repo contains build code and tools shared between IOHK projects.

Pinned versions of input-output-hk/nixpkgs.
Haskell.nix and nix-tools, plus package overlays and patches for cross-compiling to Windows.
Scripts for regenerating code with nix-tools.
Util functions such as source filtering.
Nix builds of development tools such as HLint, ShellCheck, Stylish Haskell, SHC, cache-s3.
Nix packages and overlay for the rust-cardano projects.

How to use in your project

Use iohk-nix by "pinning" its git revision and source hash in a JSON file. Then use iohk-nix to get nixpkgs. This is usually done with the default arguments to default.nix. For example:

# default.nix
{ config ? {}
, system ? builtins.currentSystem
, iohkLib ? import ./nix/iohk-common.nix { inherit config system; }
, pkgs ? iohkLib.pkgs
}:

{
  # your builds go here
}

The config and system arguments above are needed when building for other systems. They have default values, and should be passed through to iohk-nix.

Now set up ./nix/iohk-common.nix, which is pure boilerplate:

let
  spec = builtins.fromJSON (builtins.readFile ./iohk-nix.json);
in import (builtins.fetchTarball {
  url = "${spec.url}/archive/${spec.rev}.tar.gz";
  inherit (spec) sha256;
})

And create iohk-nix.json. You will need nix-prefetch-git (get it with nix-env -iA or nix-shell -p). The --rev option defaults to the HEAD of the master branch.

$ nix-prefetch-git https://github.com/input-output-hk/iohk-nix [ --rev master ] | tee ./nix/iohk-nix.json

How to update the `iohk-nix` revision.

To get the latest version of iohk-nix, update the iohk-nix.json file:

$ nix-prefetch-git https://github.com/input-output-hk/iohk-nix | tee ./nix/iohk-nix.json

Some things may have changed which could break your build, so refer to the ChangeLog.

How to use Haskell.nix and `stack-to-nix`

The documentation needs to be updated.

After updating your Stackage LTS

If you have updated your project's Stackage LTS version, then the compiler version may also have been increased.

It's possible that the nixpkgs used in iohk-nix may not have have that version of GHC, and you will get an error such as:

error: attribute 'ghc864' missing

In this case, update the iohk-nix revision to the latest available. The nixpkgs version may also need to be bumped in iohk-nix.

Nix Gotchas

The gotchas folder is dedicated to typical Nix errors encountered while developing with Haskell and Nix. The hope is developers will add Nix related problems they've encountered and solved to this folder.

Gotcha 1 - attribute unbuildable missing (win32/unix dependency issues)

When making changes to `iohk-nix`

Please document any change that might affect project builds in the ChangeLog. For example:

Bumping nixpkgs to a different branch.
Changing API (renaming attributes, changing function parameters, etc).
Bumping the haskell.nix version.

eamsden/iohk-nix