pam: add module

Also make it possible to set session variables using PAM rather than
Bash.

modules/default.nix

@@ -8,6 +8,7 @@ let
   modules = [
     ./home-environment.nix
     ./manual.nix
+    ./misc/pam.nix
     ./programs/bash.nix
     ./programs/beets.nix
     ./programs/eclipse.nix

modules/home-environment.nix

@@ -150,7 +150,24 @@ in
       default = {};
       type = types.attrs;
       example = { EDITOR = "emacs"; GS_OPTIONS = "-sPAPERSIZE=a4"; };
-      description = "Environment variables to always set at login.";
+      description = ''
+        Environment variables to always set at login.
+      '';
+    };
+
+    home.sessionVariableSetter = mkOption {
+      default = "pam";
+      type = types.enum [ "pam" "bash" ];
+      example = "bash";
+      description = ''
+        Identifies the module that should set the session variables.
+        </para><para>
+        If "bash" is set then <varname>config.bash.enable</varname>
+        must also be enabled.
+        </para><para>
+        If "pam" is set then PAM must be used to set the system
+        environment.
+      '';
     };
 
     home.packages = mkOption {

modules/misc/pam.nix

@@ -0,0 +1,20 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+
+  homeCfg = config.home;
+
+in
+
+{
+  options = {};
+
+  config = mkIf (homeCfg.sessionVariableSetter == "pam") {
+    home.file.".pam_environment".text =
+      concatStringsSep "\n" (
+        mapAttrsToList (n: v: "${n} OVERRIDE=${v}") homeCfg.sessionVariables
+      ) + "\n";
+  };
+}

modules/programs/bash.nix

@@ -127,7 +127,8 @@ in
       home.file.".profile".text = ''
         # -*- mode: sh -*-
 
-        ${envVarsStr}
+        ${optionalString (config.home.sessionVariableSetter == "bash")
+          envVarsStr}
 
         ${cfg.profileExtra}
       '';

modules/xsession.nix

@@ -72,8 +72,12 @@ in
     home.file.".xsession" = {
       mode = "555";
       text = ''
-        # Rely on Bash to set session variables.
-        . "$HOME/.profile"
+        ${
+          # If we want bash to set the session variables then we need
+          # to pull in .profile since that's where they are.
+          optionalString (config.home.sessionVariableSetter == "bash")
+            ". \"$HOME/.profile\""
+        }
 
         systemctl --user import-environment DBUS_SESSION_BUS_ADDRESS
         systemctl --user import-environment DISPLAY