git: configure patdiff through [patdiff] git section (#6978)

This adds the ability to enable the patdiff program as git differ.
Website of the project: https://opensource.janestreet.com/patdiff/

modules/programs/git.nix

@@ -496,6 +496,17 @@ in
           '';
         };
       };
+
+      patdiff = {
+        enable = mkEnableOption "" // {
+          description = ''
+            Whether to enable the {command}`patdiff` differ.
+            See <https://opensource.janestreet.com/patdiff/>
+          '';
+        };
+
+        package = mkPackageOption pkgs "patdiff" { };
+      };
     };
   };
 
@@ -526,10 +537,11 @@ in
                   cfg.difftastic.enable
                   cfg.diff-highlight.enable
                   cfg.riff.enable
+                  cfg.patdiff.enable
                 ];
               in
               lib.count lib.id enabled <= 1;
-            message = "Only one of 'programs.git.delta.enable' or 'programs.git.difftastic.enable' or 'programs.git.diff-so-fancy.enable' or 'programs.git.diff-highlight' can be set to true at the same time.";
+            message = "Only one of 'programs.git.delta.enable' or 'programs.git.difftastic.enable' or 'programs.git.diff-so-fancy.enable' or 'programs.git.diff-highlight' or 'programs.git.patdiff' can be set to true at the same time.";
           }
         ];
 
@@ -902,6 +914,20 @@ in
         }
       )
 
+      (
+        let
+          patdiffPackage = cfg.patdiff.package;
+          patdiffCommand = "${lib.getExe' patdiffPackage "patdiff-git-wrapper"}";
+        in
+        mkIf cfg.patdiff.enable {
+          home.packages = [ patdiffPackage ];
+
+          programs.git.iniContent = {
+            diff.external = patdiffCommand;
+          };
+        }
+      )
+
       (mkIf (cfg.riff.enable && cfg.riff.commandLineOptions != "") {
         home.sessionVariables.RIFF = cfg.riff.commandLineOptions;
       })

tests/darwinScrublist.nix

@@ -45,6 +45,7 @@ let
     "gh-dash"
     "ghostty"
     "git"
+    "patdiff"
     "gitMinimal"
     "git-cliff"
     "git-credential-oauth"

tests/modules/programs/git/default.nix

@@ -9,4 +9,5 @@
   git-without-signing = ./git-without-signing.nix;
   git-with-hooks = ./git-with-hooks.nix;
   git-with-maintenance = ./git-with-maintenance.nix;
+  git-patdiff = ./git-patdiff.nix;
 }

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

@@ -0,0 +1,19 @@
+[commit]
+	gpgSign = true
+
+[diff]
+	external = "@patdiff@/bin/patdiff-git-wrapper"
+
+[gpg]
+	format = "openpgp"
+
+[gpg "openpgp"]
+	program = "path-to-gpg"
+
+[tag]
+	gpgSign = true
+
+[user]
+	email = "user@example.org"
+	name = "John Doe"
+	signingKey = "00112233445566778899AABBCCDDEEFF"

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

@@ -0,0 +1,20 @@
+{
+  programs.git = {
+    enable = true;
+    signing = {
+      signer = "path-to-gpg";
+      format = "openpgp";
+      key = "00112233445566778899AABBCCDDEEFF";
+      signByDefault = true;
+    };
+    userEmail = "user@example.org";
+    userName = "John Doe";
+
+    patdiff.enable = true;
+  };
+
+  nmt.script = ''
+    assertFileExists home-files/.config/git/config
+    assertFileContent home-files/.config/git/config ${./git-patdiff-expected.conf}
+  '';
+}