delta: add jujutsu integration option

modules/programs/delta.nix

@@ -64,6 +64,16 @@ in
       '';
     };
 
+    enableJujutsuIntegration = mkOption {
+      type = types.bool;
+      default = false;
+      description = ''
+        Whether to enable jujutsu integration for delta.
+
+        When enabled, delta will be configured as jujutsus's pager, diff filter, and merge tool.
+      '';
+    };
+
     finalPackage = mkOption {
       type = types.package;
       readOnly = true;
@@ -123,5 +133,18 @@ in
             delta = cfg.options;
           };
       })
+
+      (lib.mkIf (cfg.enable && cfg.enableJujutsuIntegration) {
+        programs.jujutsu.settings = {
+          merge-tools.delta.diff-expected-exit-codes = [
+            0
+            1
+          ];
+          ui = {
+            diff-formatter = ":git";
+            pager = "${lib.getExe cfg.package}";
+          };
+        };
+      })
     ];
 }

tests/modules/programs/delta/default.nix

@@ -3,5 +3,7 @@
   delta-final-package = ./delta-final-package.nix;
   delta-with-git-integration = ./delta-with-git-integration.nix;
   delta-without-git-integration = ./delta-without-git-integration.nix;
+  delta-with-jujutsu-integration = ./delta-with-jujutsu-integration.nix;
+  delta-without-jujutsu-integration = ./delta-without-jujutsu-integration.nix;
   delta-migration = ./delta-migration.nix;
 }

tests/modules/programs/delta/delta-with-jujutsu-integration.nix

@@ -0,0 +1,21 @@
+{ config, lib, ... }:
+{
+  programs.delta = {
+    enable = true;
+    enableJujutsuIntegration = true;
+  };
+
+  programs.jujutsu.enable = true;
+
+  nmt.script = ''
+    assertFileExists home-files/.config/jj/config.toml
+    assertFileContent home-files/.config/jj/config.toml ${builtins.toFile "expected" ''
+      [merge-tools.delta]
+      diff-expected-exit-codes = [0, 1]
+
+      [ui]
+      diff-formatter = ":git"
+      pager = "${lib.getExe config.programs.delta.package}"
+    ''}
+  '';
+}

tests/modules/programs/delta/delta-without-jujutsu-integration.nix

@@ -0,0 +1,10 @@
+{
+  programs.delta = {
+    enable = true;
+    enableJujutsuIntegration = false;
+  };
+
+  nmt.script = ''
+    assertPathNotExists home-files/.config/jj/config.toml
+  '';
+}