zed-editor: fix always generating settings.json

Makes it so settings.json no longer gets made by ensuring it can be
empty as expected when there are no extensions or userSettings
defined.

PR #6201

modules/programs/zed-editor.nix

@@ -6,10 +6,11 @@ let
   cfg = config.programs.zed-editor;
   jsonFormat = pkgs.formats.json { };
 
-  mergedSettings = cfg.userSettings // {
-    # this part by @cmacrae
-    auto_install_extensions = lib.genAttrs cfg.extensions (_: true);
-  };
+  mergedSettings = cfg.userSettings
+    // (lib.optionalAttrs (builtins.length cfg.extensions > 0) {
+      # this part by @cmacrae
+      auto_install_extensions = lib.genAttrs cfg.extensions (_: true);
+    });
 in {
   meta.maintainers = [ hm.maintainers.libewa ];
 

tests/modules/programs/zed-editor/settings.nix

@@ -17,7 +17,6 @@
   nmt.script = let
     expectedContent = builtins.toFile "expected.json" ''
       {
-        "auto_install_extensions": {},
         "buffer_font_size": 16,
         "features": {
           "copilot": false