[CI] Testing flake-update showing dynamic contents

diff-closures/default.nix

@@ -0,0 +1,20 @@
+{inputs, ...}: {
+  perSystem = {
+    pkgs,
+    self',
+    ...
+  }: {
+    packages.diff-closures = pkgs.writeShellApplication {
+      name = "diff-closures";
+      runtimeInputs = [ pkgs.ansifilter ];
+      text = ''
+        nix store diff-closures --derivation \
+          github:aciceri/emacs/master#ccrEmacs \
+          "${inputs.self}#ccrEmacs" \
+        | ansifilter --text
+      '';
+    };
+    
+    apps.diff-closures.program = "${self'.packages.diff-closures}/bin/diff-closures";
+  };
+}