Make git config nix-darwin-aware

modules/futureware.nix

@@ -1,23 +1,38 @@
 # This module is supposed to be used on internal FutureWare servers.
 
-{
-  programs.git.enable = true;
-  programs.git.config = {
+{ lib, options, ... }:
+
+let
+  gitConfig = {
     url."https://git.sheremet.ch/futureware-tech/nix.git".insteadOf =
       "https://github.com/futureware-tech/nix.git";
     url."https://git.sheremet.ch/artem/dotfiles.git".insteadOf =
       "https://github.com/dotdoom/dotfiles.git";
     url."https://git.sheremet.ch/home/esphome.git".insteadOf = "https://github.com/dotdoom/esphome.git";
   };
+  hasGitOption = options ? programs.git;
+in
+lib.mkMerge [
+  {
+    nix.settings = {
+      substituters = [
+        "http://nix-cache.home.arpa"
+        # nix-community cachix server
+        # TODO: this, but through our cache -- "https://nix-community.cachix.org"
+      ];
+      trusted-public-keys = [
+        # "nix-community.cachix.org-1:mB9FSh9qf2dCimDSUo8Zy7bkq5CX+/rkCWyvRCYg3Fs="
+      ];
+    };
+  }
 
-  nix.settings = {
-    substituters = [
-      "http://nix-cache.home.arpa"
-      # nix-community cachix server
-      # TODO: this, but through our cache -- "https://nix-community.cachix.org"
-    ];
-    trusted-public-keys = [
-      # "nix-community.cachix.org-1:mB9FSh9qf2dCimDSUo8Zy7bkq5CX+/rkCWyvRCYg3Fs="
-    ];
-  };
-}
+  (lib.mkIf hasGitOption {
+    programs.git.enable = true;
+    programs.git.config = gitConfig;
+  })
+
+  (lib.mkIf (!hasGitOption) {
+    # nix-darwin
+    environment.etc."gitconfig".text = lib.generators.toGitINI gitConfig;
+  })
+]