firefox: fix build failure when package is null

Native messaging hosts module assumed all hosts are packages, and we
were passing null before.

The patch also adds a test case for a null firefox package to avoid
regressions in the future for this common (on Darwin at least) scenario.

Note: Thunderbird doesn't need a similar change because it doesn't allow
a null package.

Signed-off-by: Ihar Hrachyshka <ihar.hrachyshka@gmail.com>

modules/programs/firefox/mkFirefoxModule.nix

@@ -847,9 +847,9 @@ in {
 
     home.packages = lib.optional (cfg.finalPackage != null) cfg.finalPackage;
 
-    mozilla.firefoxNativeMessagingHosts = [
-      cfg.finalPackage # package configured native messaging hosts (entire browser actually)
-    ] ++ cfg.nativeMessagingHosts; # user configured native messaging hosts
+    mozilla.firefoxNativeMessagingHosts = cfg.nativeMessagingHosts
+      # package configured native messaging hosts (entire browser actually)
+      ++ (lib.optional (cfg.finalPackage != null) cfg.finalPackage);
 
     home.file = mkMerge ([{
       "${cfg.configPath}/profiles.ini" =

tests/modules/programs/firefox/common.nix

@@ -1,6 +1,7 @@
 name:
 builtins.mapAttrs (test: module: import module [ "programs" name ]) {
   "${name}-deprecated-native-messenger" = ./deprecated-native-messenger.nix;
+  "${name}-null-package" = ./null-package.nix;
   "${name}-final-package" = ./final-package.nix;
   "${name}-policies" = ./policies.nix;
   "${name}-profiles-bookmarks" = ./profiles/bookmarks;

tests/modules/programs/firefox/null-package.nix

@@ -0,0 +1,10 @@
+modulePath:
+{ config, lib, ... }:
+
+lib.mkIf config.test.enableBig (lib.setAttrByPath modulePath { enable = true; }
+  // {
+    programs.firefox = {
+      enable = true;
+      package = null;
+    };
+  })