Merge #2692: Use pam_env to properly setup system-wide env

nixos/modules/config/system-environment.nix

@@ -0,0 +1,56 @@
+# This module defines a system-wide environment that will be
+# initialised by pam_env (that is, not only in shells).
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+
+  cfg = config.environment;
+
+in
+
+{
+
+  options = {
+
+    environment.systemVariables = mkOption {
+      default = {};
+      description = ''
+        A set of environment variables used in the global environment.
+        These variables will be set by PAM.
+        The value of each variable can be either a string or a list of
+        strings.  The latter is concatenated, interspersed with colon
+        characters.
+      '';
+      type = types.attrsOf (mkOptionType {
+        name = "a string or a list of strings";
+        merge = loc: defs:
+          let
+            defs' = filterOverrides defs;
+            res = (head defs').value;
+          in
+          if isList res then concatLists (getValues defs')
+          else if lessThan 1 (length defs') then
+            throw "The option `${showOption loc}' is defined multiple times, in ${showFiles (getFiles defs)}."
+          else if !isString res then
+            throw "The option `${showOption loc}' does not have a string value, in ${showFiles (getFiles defs)}."
+          else res;
+      });
+      apply = mapAttrs (n: v: if isList v then concatStringsSep ":" v else v);
+    };
+
+  };
+
+  config = {
+
+    system.build.pamEnvironment = pkgs.writeText "pam-environment"
+       ''
+         ${concatStringsSep "\n" (
+           (mapAttrsToList (n: v: ''${n}="${concatStringsSep ":" v}"'')
+             (zipAttrsWith (const concatLists) ([ (mapAttrs (n: v: [ v ]) cfg.systemVariables) ]))))}
+       '';
+
+  };
+
+}