fix(reconcile): force replacement when nested value type changes between array and object

.changeset/fix-reconcile-array-object-type-mismatch.md

@@ -0,0 +1,5 @@
+---
+"@solidjs/signals": patch
+---
+
+reconcile: force wholesale replacement when nested value type changes between array and object

packages/solid-signals/src/store/reconcile.ts

@@ -170,6 +170,7 @@ function applyStateFast(next: any, target: any, keyFn: (item: NonNullable<any>)
         !previousValue ||
         !isWrappable(previousValue) ||
         !isWrappable(nextValue) ||
+        Array.isArray(previousValue) !== Array.isArray(nextValue) ||
         (keyFn(previousValue) != null && keyFn(previousValue) !== keyFn(nextValue))
       ) {
         tracked && setSignal(tracked, void 0);
@@ -314,6 +315,7 @@ function applyStateSlow(next: any, target: any, keyFn: (item: NonNullable<any>)
         !previousValue ||
         !isWrappable(previousValue) ||
         !isWrappable(nextValue) ||
+        Array.isArray(previousValue) !== Array.isArray(nextValue) ||
         (keyFn(previousValue) != null && keyFn(previousValue) !== keyFn(nextValue))
       ) {
         tracked && setSignal(tracked, void 0);

packages/solid-signals/tests/store/reconcile.test.ts

@@ -1,4 +1,5 @@
 import { describe, expect, test } from "vitest";
+import { createMemo, createRoot, flush } from "../../src/index.js";
 import { createStore, reconcile, snapshot } from "../../src/index.js";
 
 describe("setState with reconcile", () => {
@@ -158,6 +159,23 @@ describe("setState with reconcile", () => {
     setStore(reconcile({ value: { q: "aa" } }, "id"));
     expect(store.value).toEqual({ q: "aa" });
   });
+
+  test("Reconcile overwrite tracked array with object updates the signal node", () => {
+    const [store, setStore] = createStore<{ value: any }>({ value: [1, 2] });
+    let derived: any;
+
+    // Establish a tracking subscription on store.value so a signal node is created for it
+    createRoot(() => {
+      derived = createMemo(() => store.value);
+    });
+    expect(Array.isArray(derived())).toBe(true);
+
+    setStore(reconcile({ value: { a: 1 } }, "id"));
+    flush();
+
+    expect(Array.isArray(derived())).toBe(false);
+    expect((derived() as any).a).toBe(1);
+  });
 });
 // type tests