Merge branch 'fast-eval' into 'develop'

Speed up evaluation of grids by evaluating custom packages once.

See merge request !246

morph/lib/default.nix

@@ -26,6 +26,13 @@
         "megacli"
       ];
     };
-    overlays = [];
+    # Expose `nixos/pkgs` as an attribute of our package set.
+    # This is is primarly consumed by `nixos/modules/packages.nix`, which
+    # then exposes it as a module argument. We do this here, so that
+    # the package set only needs to be evaluted once for the grid, rather
+    # than once for each host.
+    overlays = [
+      (self: super: { ourpkgs = self.callPackage ../../nixos/pkgs {}; })
+    ];
   };
 }

nixos/modules/packages.nix

 # A NixOS module which exposes custom packages to other modules.
 { pkgs, ...}:
 let
-  ourpkgs = pkgs.callPackage ../../nixos/pkgs {};
+  # Get our custom packages; either from the nixpkgs attribute added via an
+  # overlay in `morph/lib/default.nix`, or by importing them directly.
+  ourpkgs = pkgs.ourpkgs or (pkgs.callPackage ../pkgs {});
 in {
   config = {
     # Expose `nixos/pkgs` as a new module argument `ourpkgs`.

nixos/system-tests.nix

 # The overall system test suite for PrivateStorageio NixOS configuration.
 { pkgs }:
-{
-  private-storage = pkgs.nixosTest ./tests/private-storage.nix;
-  spending = pkgs.nixosTest ./tests/spending.nix;
-  tahoe = pkgs.nixosTest ./tests/tahoe.nix;
+let
+  # Add custom packages as an attribute, so it they only need to be evalutated once.
+  # See the comment in `morph/lib/default.nix` for details.
+  pkgs' = pkgs.extend (self: super: { ourpkgs = self.callPackage ./pkgs {}; });
+in {
+  private-storage = pkgs'.nixosTest ./tests/private-storage.nix;
+  spending = pkgs'.nixosTest ./tests/spending.nix;
+  tahoe = pkgs'.nixosTest ./tests/tahoe.nix;
 }