fix(reactivity): unlink effect scopes on out-of-order off (#14734)

close #14733

packages/reactivity/__tests__/effectScope.spec.ts

@@ -296,6 +296,25 @@ describe('reactivity/effect/scope', () => {
     })
   })
 
+  it('calling .off() out of order should unlink the scope from the active chain', () => {
+    const parentScope = effectScope(true)
+    const firstScope = effectScope(true)
+    const secondScope = effectScope(true)
+
+    parentScope.on()
+    firstScope.on()
+    secondScope.on()
+
+    firstScope.off()
+    expect(getCurrentScope()).toBe(secondScope)
+
+    secondScope.off()
+    expect(getCurrentScope()).toBe(parentScope)
+
+    parentScope.off()
+    expect(getCurrentScope()).toBeUndefined()
+  })
+
   it('should pause/resume EffectScope', async () => {
     const counter = reactive({ num: 0 })
     const fnSpy = vi.fn(() => counter.num)

packages/reactivity/src/effectScope.ts

@@ -124,7 +124,26 @@ export class EffectScope {
    */
   off(): void {
     if (this._on > 0 && --this._on === 0) {
-      activeEffectScope = this.prevScope
+      // Fast path: in the common LIFO case this scope is still at the top
+      // of the active chain, so we can restore the previous scope directly.
+      if (activeEffectScope === this) {
+        activeEffectScope = this.prevScope
+      } else {
+        // withAsyncContext() restores the current component scope for the
+        // current async continuation, then defers its cleanup to a microtask.
+        // If sibling continuations interleave (A restore -> B restore ->
+        // A cleanup), activeEffectScope is already B instead of this scope A
+        // when A's cleanup calls off(). Unlink A from the middle of the
+        // active chain so a stale scope doesn't remain globally reachable.
+        let current = activeEffectScope
+        while (current) {
+          if (current.prevScope === this) {
+            current.prevScope = this.prevScope
+            break
+          }
+          current = current.prevScope
+        }
+      }
       this.prevScope = undefined
     }
   }

packages/server-renderer/__tests__/ssrWatch.spec.ts

@@ -3,6 +3,7 @@ import {
   defineComponent,
   h,
   nextTick,
+  onScopeDispose,
   ref,
   watch,
   watchEffect,
@@ -10,6 +11,14 @@ import {
 } from 'vue'
 import { type SSRContext, renderToString } from '../src'
 
+const gc = () =>
+  new Promise<void>(resolve => {
+    setTimeout(() => {
+      global.gc!()
+      resolve()
+    })
+  })
+
 describe('ssr: watch', () => {
   // #6013
   test('should work w/ flush:sync', async () => {
@@ -284,3 +293,62 @@ describe('ssr: watchEffect', () => {
     expect(msg).toBe('unchanged')
   })
 })
+
+describe.skipIf(!global.gc)('ssr: watch gc', () => {
+  test('should not retain apps when a watcher stop handle is registered with onScopeDispose after async context restore', async () => {
+    const weakRefs: { deref(): unknown | undefined }[] = []
+
+    const ComponentA = defineComponent({
+      async setup() {
+        let __temp: any, __restore: any
+        ;[__temp, __restore] = withAsyncContext(() => Promise.resolve(false))
+        const enabled = await __temp
+        __restore()
+
+        const el = ref(null)
+        const stop = watch(
+          () => el.value,
+          () => {},
+          { immediate: true },
+        )
+        onScopeDispose(stop)
+
+        return () => h('div', { ref: el }, `Component A ${enabled}`)
+      },
+    })
+
+    const ComponentB = defineComponent({
+      async setup() {
+        let __temp: any, __restore: any
+        ;[__temp, __restore] = withAsyncContext(() => Promise.resolve(false))
+        const enabled = await __temp
+        __restore()
+
+        return () => h('div', `Component B ${enabled}`)
+      },
+    })
+
+    async function renderOnce() {
+      const app = createSSRApp({
+        render: () => h('div', [h(ComponentA), h(ComponentB)]),
+      })
+      // @ts-expect-error ES2021 API
+      weakRefs.push(new WeakRef(app))
+
+      const html = await renderToString(app)
+
+      expect(html).toContain('Component A false')
+      expect(html).toContain('Component B false')
+    }
+
+    for (let i = 0; i < 10; i++) {
+      await renderOnce()
+    }
+
+    for (let i = 0; i < 5; i++) {
+      await gc()
+    }
+
+    expect(weakRefs.filter(ref => ref.deref()).length).toBe(0)
+  })
+})

vitest.config.ts

@@ -56,9 +56,19 @@ export default defineConfig({
             ...configDefaults.exclude,
             '**/e2e/**',
             '**/{vue,vue-compat,runtime-dom}/**',
+            'packages/server-renderer/__tests__/ssrWatch.spec.ts',
           ],
         },
       },
+      {
+        extends: true,
+        test: {
+          name: 'unit-gc',
+          pool: 'forks',
+          include: ['packages/server-renderer/__tests__/ssrWatch.spec.ts'],
+          execArgv: ['--expose-gc'],
+        },
+      },
       {
         extends: true,
         test: {