tv nixpkgs-overlays: init

This module allows to have per-system nixpkgs-overlays and is required
because at the moment of committing, only xu has an up-to-date stockholm
development directory in /home/tv/stockholm.

tv/1systems/xu/config.nix

@@ -155,5 +155,10 @@ with import <stockholm/lib>;
   # The NixOS release to be compatible with for stateful data such as databases.
   system.stateVersion = "15.09";
 
+  tv.nixpkgs-overlays = {
+    krebs = "/home/tv/stockholm/krebs/5pkgs";
+    tv = "/home/tv/stockholm/tv/5pkgs";
+  };
+
   virtualisation.virtualbox.host.enable = true;
 }

tv/2configs/default.nix

@@ -90,11 +90,7 @@ with import <stockholm/lib>;
       environment.variables = {
         NIX_PATH = mkForce (concatStringsSep ":" [
           "secrets=/var/src/stockholm/null"
-          "nixpkgs-overlays=${pkgs.runCommand "nixpkgs-overlays" {} ''
-            mkdir $out
-            ln -s /home/tv/stockholm/krebs/5pkgs $out/krebs
-            ln -s /home/tv/stockholm/tv/5pkgs $out/tv
-          ''}"
+          "nixpkgs-overlays=${config.tv.nixpkgs-overlays}"
           "/var/src"
         ]);
       };

tv/3modules/default.nix

@@ -6,6 +6,7 @@ _:
     ./ejabberd
     ./hosts.nix
     ./iptables.nix
+    ./nixpkgs-overlays.nix
     ./x0vncserver.nix
   ];
 }

tv/3modules/nixpkgs-overlays.nix

@@ -0,0 +1,23 @@
+with import <stockholm/lib>;
+{ config, pkgs, ... }: {
+
+  options.tv.nixpkgs-overlays = mkOption {
+    apply = src:
+      pkgs.runCommand "nixpkgs-overlays" {} ''
+        mkdir $out
+        ${concatStringsSep "\n" (mapAttrsToList (name: path:
+          "ln -s ${shell.escape path} $out/${shell.escape name}"
+        ) src)}
+      '' // {
+        inherit src;
+      };
+    type = types.attrsOf types.absolute-pathname;
+  };
+
+  config = {
+    tv.nixpkgs-overlays = {
+      krebs = mkDefault "/var/src/stockholm/krebs/5pkgs";
+      tv = mkDefault "/var/src/stockholm/tv/5pkgs";
+    };
+  };
+}