fix(signals): compare symbol keys in UNSTABLE_MEMO_OUTPUT

.changeset/unstable-memo-symbol-keys.md

@@ -0,0 +1,5 @@
+---
+"@solidjs/signals": patch
+---
+
+`UNSTABLE_MEMO_OUTPUT` compares symbol-keyed properties too, so a memo returning a fresh symbol-keyed box each run (as `dynamic` does for an in-flight promise) is no longer reported as new-but-equivalent.

packages/signals/src/core/attribution.ts

@@ -1726,10 +1726,15 @@ function shallowEquivalent(a: object, b: object): boolean {
     for (let i = 0; i < arrA.length; i++) if (arrA[i] !== arrB[i]) return false;
     return true;
   }
-  const keys = Object.keys(a);
-  if (keys.length > UNSTABLE_KEY_CAP || keys.length !== Object.keys(b).length) return false;
+  // Every own key, symbols included: a symbol-keyed box holding a fresh value
+  // each run (web's `dynamic` boxes its in-flight promise) is not equivalent.
+  const keys = Reflect.ownKeys(a);
+  if (keys.length > UNSTABLE_KEY_CAP || keys.length !== Reflect.ownKeys(b).length) return false;
   for (const key of keys) {
-    if (!(key in b) || (a as Record<string, unknown>)[key] !== (b as Record<string, unknown>)[key])
+    if (
+      !(key in b) ||
+      (a as Record<PropertyKey, unknown>)[key] !== (b as Record<PropertyKey, unknown>)[key]
+    )
       return false;
   }
   return true;

packages/signals/tests/attribution-unstable-memo.test.ts

@@ -101,6 +101,30 @@ describe("UNSTABLE_MEMO_OUTPUT", () => {
     expect(events).toHaveLength(0);
   });
 
+  it("compares symbol-keyed properties", () => {
+    const BOX = Symbol("box");
+    const [n, setN] = createSignal(1, { name: "n" });
+    const shared = {};
+    createRoot(() => {
+      const varying = createMemo(() => ({ [BOX]: { run: n() } }), { name: "varying-symbol" });
+      const same = createMemo(() => (n(), { [BOX]: shared }), { name: "same-symbol" });
+      createEffect(
+        () => (varying(), same()),
+        () => {},
+        { name: "consumer" }
+      );
+    });
+    flush();
+
+    const events = captureUnstable();
+    for (let i = 2; i <= 8; i++) {
+      setN(i);
+      flush();
+    }
+
+    expect(events.map(e => e.nodeName)).toEqual(["same-symbol"]);
+  });
+
   it("stays quiet for stable references, primitives, and non-plain shapes", () => {
     const [n, setN] = createSignal(1, { name: "n" });
     const stable = { fixed: true };