fix Object.defineProperty sharing values across instances

RealColdFry · RealColdFry · commit 697a912d159e · 2026-03-26T14:30:41.000Z
When Object.defineProperty is called on an instance (not a prototype), create a per-instance metatable if the shared metatable already has descriptors, so that each instance gets its own descriptor storage. Fixes #1625
diff --git a/src/lualib/SetDescriptor.ts b/src/lualib/SetDescriptor.ts
@@ -26,6 +26,19 @@ export function __TS__SetDescriptor(
         setmetatable(target, metatable);
     }
 
+    // When setting a descriptor on an instance (not a prototype), ensure it has
+    // its own metatable so descriptors are not shared across instances.
+    // See: https://github.com/TypeScriptToLua/TypeScriptToLua/issues/1625
+    if (!isPrototype && rawget(metatable, "_descriptors")) {
+        // The metatable already has descriptors from a previous defineProperty
+        // call (likely on a different instance sharing the same class metatable).
+        // Create a per-instance metatable that chains to the original.
+        const instanceMetatable: any = {};
+        setmetatable(instanceMetatable, metatable);
+        setmetatable(target, instanceMetatable);
+        metatable = instanceMetatable;
+    }
+
     const value = rawget(target, key);
     if (value !== undefined) rawset(target, key, undefined);
 
diff --git a/test/unit/builtins/object.spec.ts b/test/unit/builtins/object.spec.ts
@@ -196,6 +196,21 @@ describe("Object.defineProperty", () => {
             return { prop: foo.bar, err };
         `.expectToMatchJsResult();
     });
+
+    // https://github.com/TypeScriptToLua/TypeScriptToLua/issues/1625
+    test("instance isolation", () => {
+        util.testFunction`
+            class Test {
+                declare obj: object;
+                constructor() {
+                    Object.defineProperty(this, "obj", { value: {}, writable: true, configurable: true });
+                }
+            }
+            const t1 = new Test();
+            const t2 = new Test();
+            return t1.obj === t2.obj;
+        `.expectToMatchJsResult();
+    });
 });
 
 describe("Object.getOwnPropertyDescriptor", () => {
