imp: filterPackages (#28)

* imp: filterPackages

* Update filterPackages.nix

* Update filterPackages.nix

Co-authored-by: Jonas Chevalier <zimbatm@zimbatm.com>

default.nix

@@ -100,6 +100,27 @@ let
   #   }
   flattenTree = tree: import ./flattenTree.nix tree;
 
+  # Nix check functionality validates packages for various conditions, like if
+  # they build for any given platform or if they are marked broken.
+  #
+  # This function filters a flattend package set for conditinos that
+  # would *trivially* break `nix flake check`. It does not flatten a tree and it
+  # does not implement advanced package validation checks.
+  #
+  # Eg:
+  #
+  #   filterPackages "x86_64-linux" {
+  #     hello = pkgs.hello;
+  #     "gitAndTools/git" = pkgs.gitAndTools // {meta.broken = true;};
+  #    };
+  #
+  # Returns:
+  #
+  #   {
+  #      hello = «derivation»;
+  #   }
+  filterPackages = system: packages: import ./filterPackages.nix system packages;
+
   # Returns the structure used by `nix app`
   mkApp =
     { drv

filterPackages.nix

@@ -0,0 +1,28 @@
+system: packages:
+let
+  # Adopted from nixpkgs.lib
+  inherit (builtins) listToAttrs concatMap attrName;
+  nameValuePair = name: value: { inherit name value; };
+  filterAttrs = pred: set:
+    listToAttrs (
+      concatMap (name:
+        let v = set.${name}; in
+          if pred name v then [(nameValuePair name v)] else []
+      )
+      (attrNames set)
+    );
+
+  # Everything that nix flake check requires for the packages output
+  sieve = n: v:
+    with v;
+    let
+      inherit (builtins) isAttrs;
+      isDerivation = x: isAttrs x && x ? type && x.type == "derivation";
+      platforms = meta.hydraPlatforms or meta.platforms or [ ];
+    in
+      # check for isDerivation, so this is independently useful of
+      # flattenTree, which also does filter on derviations
+      isDerivation v && !meta.broken && builtins.elem system platforms
+  ;
+in
+filterAttrs sieve packages