Package Settings

Settings for individual Haskell packages can be specified in the settings attribute of a haskellProjects module.

haskellProjects.default = {
  settings = {
    ema = {  # This module can take `{self, super, ...}` args, optionally.
      # Disable running tests
      check = false;

      # Disable building haddock (documentation)
      haddock = false;

      # Ignore Cabal version constraints
      jailbreak = true;

      # Extra non-Haskell dependencies
      extraBuildDepends = [ pkgs.stork ];

      # Library-specific dependencies
      librarySystemDepends = [ pkgs.zlib ];
      libraryPkgconfigDepends = [ pkgs.openssl ];

      # Source patches
      patches = [ ./patches/ema-bug-fix.patch ];

      # Enable/disable Cabal flags
      cabalFlags.with-generics = true;

      # Allow building a package marked as "broken"
      broken = false;
    };
  };
};

Sharing package settings

Project modules export both packages and settings options for reuse in downstream Haskell projects.

Custom settings

You can provide custom settings for use in multiple packages (even across multiple repos). For example, see this Emanote change which demonstrates how to add a new setting option (removeReferencesTo).

Extra settings

haskell-flake provides the following settings on top of those provided by nixpkgs.

drvAttrs

Set arbitrary attributes on the Haskell package derivation. This is a simpler alternative to the custom option for setting derivation attributes like environment variables.

settings = {
  foo = {
    drvAttrs = {
      GIT_BIN = lib.getExe' pkgs.git "git";
      SOME_ENV_VAR = "value";
    };
  };
};

Unlike custom, the drvAttrs option composes well with other settings and doesn’t require writing a function.

generateOptparseApplicativeCompletions

Generate and install shell completion files for executables. The executables need to be using optparse-applicative for this to work. Note that this feature is automatically disabled when cross-compiling, since it requires executing the binaries in question.

removeReferencesTo

Remove references to other packages from this Haskell package. This is useful to eliminate unnecessary data dependencies from your Haskell executable so as to reduce its closure size.

buildFromSdist

Newer versions of nixpkgs provide buildFromSdist to build your package from the cabal sdist tarball. This is enabled by default, to help with checking release-worthiness of your packages.

stan

Run STatic ANalysis on the package using stan and generate an HTML report. The report is created in the /nix/store path alongside your package outputs.