From a7c06f1ff6d9bec04eb974c44ad04f461441c471 Mon Sep 17 00:00:00 2001
From: Cold Fry <coldfry.business@gmail.com>
Date: Tue, 17 Mar 2026 19:06:52 +0000
Subject: [PATCH] fix Set iterator not reflecting mutations after creation
 (#1671)

Set.values(), keys(), and entries() eagerly captured firstKey at
iterator creation time. If the Set was mutated (e.g. via delete)
before the iterator was consumed, the iterator still saw the stale
firstKey. Read firstKey lazily on the first next() call instead.
---
 src/lualib/Set.ts              | 42 ++++++++++++++++++++++++----------
 test/unit/builtins/set.spec.ts | 13 +++++++++++
 2 files changed, 43 insertions(+), 12 deletions(-)

diff --git a/src/lualib/Set.ts b/src/lualib/Set.ts
index b46555edf..e302e4094 100644
--- a/src/lualib/Set.ts
+++ b/src/lualib/Set.ts
@@ -102,46 +102,64 @@ export class Set<T extends AnyNotNil> {
     }
 
     public entries(): IterableIterator<[T, T]> {
+        const getFirstKey = () => this.firstKey;
         const nextKey = this.nextKey;
-        let key: T = this.firstKey!;
+        let key: T | undefined;
+        let started = false;
         return {
             [Symbol.iterator](): IterableIterator<[T, T]> {
                 return this;
             },
             next(): IteratorResult<[T, T]> {
-                const result = { done: !key, value: [key, key] as [T, T] };
-                key = nextKey.get(key);
-                return result;
+                if (!started) {
+                    started = true;
+                    key = getFirstKey();
+                } else {
+                    key = nextKey.get(key!);
+                }
+                return { done: !key, value: [key!, key!] as [T, T] };
             },
         };
     }
 
     public keys(): IterableIterator<T> {
+        const getFirstKey = () => this.firstKey;
         const nextKey = this.nextKey;
-        let key: T = this.firstKey!;
+        let key: T | undefined;
+        let started = false;
         return {
             [Symbol.iterator](): IterableIterator<T> {
                 return this;
             },
             next(): IteratorResult<T> {
-                const result = { done: !key, value: key };
-                key = nextKey.get(key);
-                return result;
+                if (!started) {
+                    started = true;
+                    key = getFirstKey();
+                } else {
+                    key = nextKey.get(key!);
+                }
+                return { done: !key, value: key! };
             },
         };
     }
 
     public values(): IterableIterator<T> {
+        const getFirstKey = () => this.firstKey;
         const nextKey = this.nextKey;
-        let key: T = this.firstKey!;
+        let key: T | undefined;
+        let started = false;
         return {
             [Symbol.iterator](): IterableIterator<T> {
                 return this;
             },
             next(): IteratorResult<T> {
-                const result = { done: !key, value: key };
-                key = nextKey.get(key);
-                return result;
+                if (!started) {
+                    started = true;
+                    key = getFirstKey();
+                } else {
+                    key = nextKey.get(key!);
+                }
+                return { done: !key, value: key! };
             },
         };
     }
diff --git a/test/unit/builtins/set.spec.ts b/test/unit/builtins/set.spec.ts
index a03f27ab2..cbf4ff418 100644
--- a/test/unit/builtins/set.spec.ts
+++ b/test/unit/builtins/set.spec.ts
@@ -195,6 +195,19 @@ describe.each(iterationMethods)("set.%s() preserves insertion order", iterationM
     });
 });
 
+test("set iterator persists after delete", () => {
+    util.testFunction`
+        const set1 = new Set<string | number>();
+        set1.add(42);
+        set1.add("forty two");
+
+        const iterator1 = set1.values();
+        set1.delete(42);
+
+        return iterator1.next().value;
+    `.expectToMatchJsResult();
+});
+
 test("instanceof Set without creating set", () => {
     util.testFunction`
         const myset = 3 as any;