nix/default.nix: make globals into a parameter

Author: deepfire

nix/default.nix

@@ -1,6 +1,11 @@
 { system ? builtins.currentSystem
 , crossSystem ? null
 , config ? {}
+, deploymentGlobalsFn ? ## :: Pkgs -> GlobalsOverlayOverDefaults
+    pkgs:
+    if builtins.pathExists ../globals.nix
+    then import ../globals.nix pkgs
+    else builtins.trace "globals.nix missing, please add symlink" {}
 }:
 let
   defaultSourcePaths = import ./sources.nix { inherit pkgs; };
@@ -90,20 +95,20 @@ let
     (import ./packages.nix)
   ];
 
-  globals =
-    if builtins.pathExists ../globals.nix
-    then [(pkgs: _: with pkgs.lib; let
+  buildGlobals =
+    specificGlobalsFn:
+
+    [(pkgs: _: with pkgs.lib; let
       globalsDefault = import ../globals-defaults.nix pkgs;
-      globalsSpecific = import ../globals.nix pkgs;
+      globalsSpecific = specificGlobalsFn pkgs;
     in {
       globals = globalsDefault // (recursiveUpdate {
         inherit (globalsDefault) ec2 libvirtd environmentVariables;
       } globalsSpecific);
-    })]
-    else builtins.trace "globals.nix missing, please add symlink" [(pkgs: _: {
-      globals = import ../globals-defaults.nix pkgs;
     })];
 
+  globals = buildGlobals deploymentGlobalsFn;
+
   # merge upstream sources with our own:
   upstream-overlay = self: super: {
       inherit iohkNix;