fix(reconcile): notify ownKeys subscribers on pure keyed trailing removal

.changeset/fix-reconcile-trailing-removal-notify.md

@@ -0,0 +1,5 @@
+---
+"@solidjs/signals": patch
+---
+
+reconcile: notify ownKeys subscribers on pure keyed trailing removal

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

@@ -99,7 +99,7 @@ function applyStateFast(next: any, target: any, keyFn: (item: NonNullable<any>)
           applyState(next[j], wrapped, keyFn);
         }
 
-        changed && notifySelf(target);
+        (changed || prevLength !== next.length) && notifySelf(target);
         prevLength !== next.length &&
           arrayNodes?.length &&
           setSignal(arrayNodes.length, next.length);
@@ -244,7 +244,7 @@ function applyStateSlow(next: any, target: any, keyFn: (item: NonNullable<any>)
         }
 
         const nextLength = next.length;
-        changed && notifySelf(target);
+        (changed || prevLength !== nextLength) && notifySelf(target);
         prevLength !== nextLength && nodes?.length && setSignal(nodes.length, nextLength);
         return;
       }

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

@@ -1,5 +1,5 @@
 import { describe, expect, test } from "vitest";
-import { createStore, reconcile, snapshot } from "../../src/index.js";
+import { createStore, reconcile, snapshot, $TRACK, createMemo, createRoot, createEffect, createRenderEffect, flush } from "../../src/index.js";
 
 describe("setState with reconcile", () => {
   test("Reconcile a simple object", () => {
@@ -158,6 +158,27 @@ describe("setState with reconcile", () => {
     setStore(reconcile({ value: { q: "aa" } }, "id"));
     expect(store.value).toEqual({ q: "aa" });
   });
+  test("Reconcile keyed trailing removal notifies $TRACK subscribers", () => {
+    let effectRunCount = 0;
+    const [state, setState] = createStore({ arr: [{ id: 1 }, { id: 2 }, { id: 3 }] });
+    createRoot(() => {
+      createRenderEffect(() => {
+        effectRunCount++;
+        // accessing $TRACK subscribes to ownKeys notifications on arr
+        (state.arr as any)[$TRACK];
+        return undefined;
+      }, () => undefined);
+    });
+    // flush to run the effect initially
+    flush();
+    const runsBefore = effectRunCount;
+    setState(s => {
+      reconcile([{ id: 1 }, { id: 2 }], "id")(s.arr);
+    });
+    // flush to propagate invalidation and re-run the effect
+    flush();
+    expect(effectRunCount).toBeGreaterThan(runsBefore);
+  });
 });
 // type tests