From 923dc7f92c62fe06f5b2cd16773bccbe1eecfb17 Mon Sep 17 00:00:00 2001
From: Jeff Repanich <jrepanich@gmail.com>
Date: Mon, 24 Aug 2026 09:58:03 -0400
Subject: [PATCH] test: cover adversarial runtime concurrency

---
 tests/jsdom/runtime/hardening-matrix.test.tsx | 185 ++++++++++++++++++
 1 file changed, 185 insertions(+)
 create mode 100644 tests/jsdom/runtime/hardening-matrix.test.tsx

diff --git a/tests/jsdom/runtime/hardening-matrix.test.tsx b/tests/jsdom/runtime/hardening-matrix.test.tsx
new file mode 100644
index 00000000..3f904a3d
--- /dev/null
+++ b/tests/jsdom/runtime/hardening-matrix.test.tsx
@@ -0,0 +1,185 @@
+import { describe, expect, it } from 'vite-plus/test';
+import { cleanupApp } from '../../../src/boot';
+import { For } from '../../../src/control';
+import { state, type State } from '../../../src/index';
+import { resource } from '../../../src/resources';
+import { globalScheduler, Scheduler } from '../../../src/runtime/scheduler';
+import { createIsland } from '../../../test-utils/render/create-island';
+import {
+  createTestContainer,
+  flushScheduler,
+} from '../../../test-utils/render/test-renderer';
+
+async function settleResourceWork(): Promise<void> {
+  await Promise.resolve();
+  await Promise.resolve();
+  flushScheduler();
+}
+
+describe('core hardening matrix', () => {
+  it('should settle overlapping and already-superseded flush waiters', async () => {
+    const scheduler = new Scheduler();
+    scheduler.enqueue(() => {});
+    const first = scheduler.waitForFlush(1);
+    const second = scheduler.waitForFlush(2);
+
+    scheduler.flush();
+    await first;
+    let secondSettled = false;
+    void second.then(() => {
+      secondSettled = true;
+    });
+    await Promise.resolve();
+    expect(secondSettled).toBe(false);
+
+    scheduler.enqueue(() => {});
+    scheduler.flush();
+    await second;
+    await expect(scheduler.waitForFlush(1)).resolves.toBeUndefined();
+  });
+
+  it('should serialize a state write made reentrantly inside another updater', () => {
+    const { container, cleanup } = createTestContainer();
+    let first!: State<number>;
+    let second!: State<number>;
+
+    try {
+      createIsland({
+        root: container,
+        component: () => {
+          first = state(1);
+          second = state(10);
+          return <output>{`${String(first())}:${String(second())}`}</output>;
+        },
+      });
+
+      first.set((previous) => {
+        second.set((other) => other + 5);
+        return previous + 1;
+      });
+      flushScheduler();
+
+      expect(container.textContent).toBe('2:15');
+    } finally {
+      cleanup();
+    }
+  });
+
+  it('should make state work inert when its owner unmounts during an active flush', () => {
+    const { container, cleanup } = createTestContainer();
+    let value!: State<number>;
+    let renders = 0;
+
+    try {
+      createIsland({
+        root: container,
+        component: () => {
+          renders += 1;
+          value = state(0);
+          return <output>{String(value())}</output>;
+        },
+      });
+
+      globalScheduler.enqueue(() => cleanupApp(container));
+      globalScheduler.enqueue(() => value.set(1));
+      expect(() => flushScheduler()).not.toThrow();
+      expect(renders).toBe(1);
+      expect(globalScheduler.getState().queueLength).toBe(0);
+    } finally {
+      cleanup();
+    }
+  });
+
+  it('should isolate two resources sharing a changing dependency across resolution races', async () => {
+    const { container, cleanup } = createTestContainer();
+    const firstResolvers = new Map<string, (value: string) => void>();
+    const secondResolvers = new Map<string, (value: string) => void>();
+    let dependency!: State<string>;
+
+    try {
+      createIsland({
+        root: container,
+        component: () => {
+          dependency = state('old');
+          const key = dependency();
+          const first = resource(
+            () =>
+              new Promise<string>((resolve) => {
+                firstResolvers.set(key, resolve);
+              }),
+            [key]
+          );
+          const second = resource(
+            () =>
+              new Promise<string>((resolve) => {
+                secondResolvers.set(key, resolve);
+              }),
+            [key]
+          );
+          return (
+            <output>{`${first.value ?? '-'}:${second.value ?? '-'}`}</output>
+          );
+        },
+      });
+      await settleResourceWork();
+
+      dependency.set('new');
+      flushScheduler();
+      await settleResourceWork();
+      secondResolvers.get('new')!('second:new');
+      firstResolvers.get('new')!('first:new');
+      await settleResourceWork();
+      expect(container.textContent).toBe('first:new:second:new');
+
+      firstResolvers.get('old')!('first:old');
+      secondResolvers.get('old')!('second:old');
+      await settleResourceWork();
+      expect(container.textContent).toBe('first:new:second:new');
+    } finally {
+      cleanup();
+    }
+  });
+
+  it('should reconcile two independent For lists in the same flush', () => {
+    const { container, cleanup } = createTestContainer();
+    let first!: State<string[]>;
+    let second!: State<string[]>;
+
+    try {
+      createIsland({
+        root: container,
+        component: () => {
+          first = state(['a', 'b']);
+          second = state(['x', 'y']);
+          return (
+            <main>
+              <ol data-list="first">
+                <For each={() => first()} by={(item) => item}>
+                  {(item) => <li>{item}</li>}
+                </For>
+              </ol>
+              <ol data-list="second">
+                <For each={() => second()} by={(item) => item}>
+                  {(item) => <li>{item}</li>}
+                </For>
+              </ol>
+            </main>
+          );
+        },
+      });
+
+      first.set(['b', 'c', 'a']);
+      second.set(['y', 'z']);
+      flushScheduler();
+
+      const text = (selector: string) =>
+        Array.from(container.querySelectorAll(`${selector} li`)).map(
+          (item) => item.textContent
+        );
+      expect(text('[data-list="first"]')).toEqual(['b', 'c', 'a']);
+      expect(text('[data-list="second"]')).toEqual(['y', 'z']);
+    } finally {
+      cleanup();
+    }
+  });
+});