haskell.nix/ci-lib.nix

let
  # Generic nixpkgs, use *only* for lib functions that are stable across versions
  pkgs = import (import ./nixpkgs/default.nix).nixpkgs-default {};
  lib = pkgs.lib;
in rec {
  inherit (import ./dimension.nix) dimension;

  # A filter for removing packages that aren't supported on the current platform
  # according to 'meta.platforms'.
  platformFilterGeneric = pkgs: system:
    # This needs to use the correct nixpkgs version so all the systems line up
    let lib = pkgs.lib;
        platform = lib.systems.elaborate { inherit system; };
    # Can't just default to [] for platforms, since no meta.platforms
    # means "all platforms" not "no platforms"
    in drv : if drv ? meta && drv.meta ? platforms then
      lib.any (lib.meta.platformMatch platform) drv.meta.platforms
    else true;

  # Hydra doesn't like these attributes hanging around in "jobsets": it thinks they're jobs!
  stripAttrsForHydra = filterAttrsOnlyRecursive (n: _: n != "recurseForDerivations" && n != "dimension");

  # Keep derivations and attrsets with 'recurseForDerivations'. This ensures that we match the
  # derivations that Hercules will see, and prevents Hydra from trying to pick up all sorts of bad stuff
  # (like attrsets that contain themselves!).
  filterDerivations = filterAttrsOnlyRecursive (n: attrs: lib.isDerivation attrs || attrs.recurseForDerivations or false);

  # A version of 'filterAttrsRecursive' that doesn't recurse into derivations. This prevents us from going into an infinite
  # loop with the 'out' attribute on derivations.
  # TODO: Surely this shouldn't be necessary. I think normal 'filterAttrsRecursive' will effectively cause infinite loops
  # if you keep derivations and your predicate forces the value of the attribute, as this then triggers a loop on the
  # 'out' attribute. Weird.
  filterAttrsOnlyRecursive = pred: set:
    lib.listToAttrs (
      lib.concatMap (name:
        let v = set.${name}; in
        if pred name v then [
          (lib.nameValuePair name (
            if builtins.isAttrs v && !lib.isDerivation v then filterAttrsOnlyRecursive pred v
            else v
          ))
        ] else []
      ) (builtins.attrNames set)
    );
}