branching and very basic merging of slots

util/util.js

@@ -12,6 +12,20 @@ export function deepEqual(a, b) {
     }
     return true;
   }
+  if (a instanceof Set) {
+    if (!(b instanceof Set)) {
+      return false;
+    }
+    if (a.size !== b.size) {
+      return false;
+    }
+    for (const entry of a) {
+      if (!b.has(entry)) {
+        return false;
+      }
+    }
+    return true;
+  }
   const keysA = Object.keys(a);
   const keysB = Object.keys(b);
   if (keysA.length !== keysB.length) return false;