git: add basic support for delta

PR #1198

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

@@ -6,6 +6,9 @@
 [commit]
 	gpgSign = true
 
+[core]
+	pager = "@deltaCommand@ --dark"
+
 [extra]
 	boolean = true
 	integer = 38
@@ -28,6 +31,9 @@
 [gpg]
 	program = "path-to-gpg"
 
+[interactive]
+	diffFilter = "@deltaCommand@ --dark --color-only"
+
 [user]
 	email = "user@example.org"
 	name = "John Doe"

tests/modules/programs/git/git.nix

@@ -15,6 +15,8 @@ let
     pkgs.substituteAll {
       src = path;
 
+      deltaCommand = "${pkgs.gitAndTools.delta}/bin/delta";
+
       git_include_path = pkgs.writeText "contents"
         (builtins.readFile ./git-expected-include.conf);
     };
@@ -56,6 +58,10 @@ in {
         userEmail = "user@example.org";
         userName = "John Doe";
         lfs.enable = true;
+        delta = {
+          enable = true;
+          options = [ "--dark" ];
+        };
       }
 
       {