sly: add update script

pkgs/by-name/sl/sly/package.nix

@@ -2,6 +2,11 @@
   lib,
   fetchFromGitHub,
   flutter327,
+  runCommand,
+  yq,
+  sly,
+  _experimental-update-script-combinators,
+  gitUpdater,
 }:
 
 flutter327.buildFlutterApplication rec {
@@ -22,6 +27,22 @@ flutter327.buildFlutterApplication rec {
     install -Dm0644 packaging/linux/page.kramo.Sly.desktop $out/share/applications/sly.desktop
   '';
 
+  passthru = {
+    pubspecSource =
+      runCommand "pubspec.lock.json"
+        {
+          nativeBuildInputs = [ yq ];
+          inherit (sly) src;
+        }
+        ''
+          cat $src/pubspec.lock | yq > $out
+        '';
+    updateScript = _experimental-update-script-combinators.sequence [
+      (gitUpdater { rev-prefix = "v"; })
+      (_experimental-update-script-combinators.copyAttrOutputToFile "sly.pubspecSource" ./pubspec.lock.json)
+    ];
+  };
+
   meta = {
     description = "Friendly image editor";
     homepage = "https://github.com/kra-mo/Sly";