fix(reactivity): ensure computed always expose value

fix #3099

Also changes the original fix for #910 by moving the fix from
reactivity to the scheduler

packages/runtime-core/__tests__/scheduler.spec.ts

@@ -1,3 +1,4 @@
+import { effect, stop } from '@vue/reactivity'
 import {
   queueJob,
   nextTick,
@@ -568,4 +569,27 @@ describe('scheduler', () => {
     await nextTick()
     expect(count).toBe(1)
   })
+
+  // #910
+  test('should not run stopped reactive effects', async () => {
+    const spy = jest.fn()
+
+    // simulate parent component that toggles child
+    const job1 = () => {
+      stop(job2)
+    }
+    job1.id = 0 // need the id to ensure job1 is sorted before job2
+
+    // simulate child that's triggered by the same reactive change that
+    // triggers its toggle
+    const job2 = effect(() => spy())
+    expect(spy).toHaveBeenCalledTimes(1)
+
+    queueJob(job1)
+    queueJob(job2)
+    await nextTick()
+
+    // should not be called again
+    expect(spy).toHaveBeenCalledTimes(1)
+  })
 })

packages/runtime-core/src/scheduler.ts

@@ -3,27 +3,14 @@ import { isArray } from '@vue/shared'
 import { ComponentPublicInstance } from './componentPublicInstance'
 import { ComponentInternalInstance, getComponentName } from './component'
 import { warn } from './warning'
+import { ReactiveEffect } from '@vue/reactivity'
 
-export interface SchedulerJob {
-  (): void
+export interface SchedulerJob extends Function, Partial<ReactiveEffect> {
   /**
-   * unique job id, only present on raw effects, e.g. component render effect
+   * Attached by renderer.ts when setting up a component's render effect
+   * Used to obtain component information when reporting max recursive updates.
+   * dev only.
    */
-  id?: number
-  /**
-   * Indicates whether the job is allowed to recursively trigger itself.
-   * By default, a job cannot trigger itself because some built-in method calls,
-   * e.g. Array.prototype.push actually performs reads as well (#1740) which
-   * can lead to confusing infinite loops.
-   * The allowed cases are component update functions and watch callbacks.
-   * Component update functions may update child component props, which in turn
-   * trigger flush: "pre" watch callbacks that mutates state that the parent
-   * relies on (#1801). Watch callbacks doesn't track its dependencies so if it
-   * triggers itself again, it's likely intentional and it is the user's
-   * responsibility to perform recursive state mutation that eventually
-   * stabilizes (#1727).
-   */
-  allowRecurse?: boolean
   ownerInstance?: ComponentInternalInstance
 }
 
@@ -243,7 +230,7 @@ function flushJobs(seen?: CountMap) {
   try {
     for (flushIndex = 0; flushIndex < queue.length; flushIndex++) {
       const job = queue[flushIndex]
-      if (job) {
+      if (job && job.active !== false) {
         if (__DEV__ && checkRecursiveUpdates(seen!, job)) {
           continue
         }