git: add extraArgs option for difftastic

This option will cover any other arguments that aren't made available
with dedicated options.

modules/programs/git.nix

@@ -377,6 +377,18 @@ in
             Determines how the output displays - in one column or two columns.
           '';
         };
+
+        extraArgs = mkOption {
+          type = types.nullOr (types.listOf types.str);
+          default = null;
+          example = [
+            "--tab-width=8"
+            "--sort-paths"
+          ];
+          description = ''
+            Extra command line arguments to pass to {command}`difft`.
+          '';
+        };
       };
 
       delta = {
@@ -837,13 +849,16 @@ in
 
       (
         let
-          difftCommand = concatStringsSep " " [
+          difftCommand = concatStringsSep " " (
+            [
               "${lib.getExe cfg.difftastic.package}"
               "--color ${cfg.difftastic.color}"
               "--background ${cfg.difftastic.background}"
               "--display ${cfg.difftastic.display}"
               "--context ${toString cfg.difftastic.context}"
-          ];
+            ]
+            ++ (lib.optionals (cfg.difftastic.extraArgs != null) cfg.difftastic.extraArgs)
+          );
         in
         (lib.mkMerge [
           (mkIf cfg.difftastic.enable {

tests/modules/programs/git/git-difftastic-expected.conf

@@ -1,9 +1,9 @@
 [diff]
-	external = "@difftastic@/bin/difft --color always --background dark --display inline --context 5"
+	external = "@difftastic@/bin/difft --color always --background dark --display inline --context 5 --tab-width=8 --sort-paths"
 	tool = "difftastic"
 
 [difftool "difftastic"]
-	cmd = "@difftastic@/bin/difft --color always --background dark --display inline --context 5 $LOCAL $REMOTE"
+	cmd = "@difftastic@/bin/difft --color always --background dark --display inline --context 5 --tab-width=8 --sort-paths $LOCAL $REMOTE"
 
 [gpg]
 	format = "openpgp"

tests/modules/programs/git/git-difftastic.nix

@@ -9,6 +9,10 @@
       color = "always";
       context = 5;
       display = "inline";
+      extraArgs = [
+        "--tab-width=8"
+        "--sort-paths"
+      ];
     };
   };