From 43845d04f83d44d744206ea9884b8206e7640633 Mon Sep 17 00:00:00 2001
From: Ayman Bagabas <ayman.bagabas@gmail.com>
Date: Wed, 11 Sep 2024 20:25:31 -0400
Subject: [PATCH] git: add diff-highlight diff pager option

This adds a new diff-highlight option to make use of the simple
included git diff highlighter that comes with canonical git.

For more info, see https://github.com/git/git/blob/master/contrib/diff-highlight/README
---
 modules/programs/git.nix | 40 +++++++++++++++++++++++++++++++++++++---
 1 file changed, 37 insertions(+), 3 deletions(-)

diff --git a/modules/programs/git.nix b/modules/programs/git.nix
index 3f5cdc7cc..07d01ab9d 100644
--- a/modules/programs/git.nix
+++ b/modules/programs/git.nix
@@ -214,6 +214,24 @@ in {
         };
       };
 
+      diff-highlight = {
+        enable = mkEnableOption "" // {
+          description = ''
+            Enable the contrib {command}`diff-highlight` syntax highlighter.
+            See <https://github.com/git/git/blob/master/contrib/diff-highlight/README>,
+          '';
+        };
+
+        pagerOpts = mkOption {
+          type = types.listOf types.str;
+          default = [ ];
+          example = [ "--tabs=4" "-RFX" ];
+          description = ''
+            Arguments to be passed to {command}`less`.
+          '';
+        };
+      };
+
       difftastic = {
         enable = mkEnableOption "" // {
           description = ''
@@ -360,11 +378,15 @@ in {
       home.packages = [ cfg.package ];
       assertions = [{
         assertion = let
-          enabled =
-            [ cfg.delta.enable cfg.diff-so-fancy.enable cfg.difftastic.enable ];
+          enabled = [
+            cfg.delta.enable
+            cfg.diff-so-fancy.enable
+            cfg.difftastic.enable
+            cfg.diff-highlight.enable
+          ];
         in count id enabled <= 1;
         message =
-          "Only one of 'programs.git.delta.enable' or 'programs.git.difftastic.enable' or 'programs.git.diff-so-fancy.enable' can be set to true at the same time.";
+          "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.";
       }];
 
       programs.git.iniContent.user = {
@@ -479,6 +501,18 @@ in {
         };
     })
 
+    (mkIf cfg.diff-highlight.enable {
+      programs.git.iniContent = let
+        dhCommand =
+          "${cfg.package}/share/git/contrib/diff-highlight/diff-highlight";
+      in {
+        core.pager = "${dhCommand} | ${getExe pkgs.less} ${
+            escapeShellArgs cfg.diff-highlight.pagerOpts
+          }";
+        interactive.diffFilter = dhCommand;
+      };
+    })
+
     (mkIf cfg.difftastic.enable {
       home.packages = [ cfg.difftastic.package ];