git: set up difftastic properly

nixos/configs/ccache.nix

@@ -0,0 +1,38 @@
+#
+# Support for using Ccache.
+#
+{ config, ... }:
+{
+  programs.ccache.enable = true;
+  nix.settings.extra-sandbox-paths = [ config.programs.ccache.cacheDir ];
+
+  nixpkgs.overlays = [
+  (self: super: {
+    ccacheWrapper = super.ccacheWrapper.override {
+      extraConfig = ''
+        export CCACHE_COMPRESS=1
+        export CCACHE_DIR="${config.programs.ccache.cacheDir}"
+        export CCACHE_UMASK=007
+        if [ ! -d "$CCACHE_DIR" ]; then
+          echo "====="
+          echo "Directory '$CCACHE_DIR' does not exist"
+          echo "Please create it with:"
+          echo "  sudo mkdir -m0770 '$CCACHE_DIR'"
+          echo "  sudo chown root:nixbld '$CCACHE_DIR'"
+          echo "====="
+          exit 1
+        fi
+        if [ ! -w "$CCACHE_DIR" ]; then
+          echo "====="
+          echo "Directory '$CCACHE_DIR' is not accessible for user $(whoami)"
+          echo "Please verify its access permissions"
+          echo "====="
+          exit 1
+        fi
+      '';
+    };
+  })
+
+  # Use this for kernel packages.
+];
+}

nixos/configs/dotfiles/git.hm.nix

@@ -1,4 +1,7 @@
 { deprekages, pkgs, ... }:
+let
+	difft = "${pkgs.difftastic}/bin/difft";
+in
 {
 
   #
@@ -11,13 +14,22 @@
     # Note: we no longer set a name, here, forcing us to choose our e-mail and username
     # on a per-project basis.
 
-    # Proide the difftastic command.
-    difftastic.enable = true;
-
     extraConfig = {
       # Use main as our branch names.
       init.defaultBranch = "main";
 
+      #
+      # Use difftastic.
+      #
+      alias = {
+        dlog = "-c diff.external=${difft} log --ext-diff";
+        dshow = "-c diff.external=${difft} show --ext-diff";
+        ddiff = "-c diff.external=${difft} diff";
+        dl = "-c diff.external=${difft} log -p --ext-diff";
+        ds = "-c diff.external=${difft} show --ext-diff";
+        dd = "-c diff.external=${difft} diff";
+      };
+
       #
       # Use mergiraf.
       #