fix(scheduler): allows to sort the PostFlushCbs

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

@@ -7,7 +7,7 @@ import {
   ref,
   h
 } from '../src/index'
-import { render, nodeOps, serializeInner } from '@vue/runtime-test'
+import { render, nodeOps, serializeInner, TestElement } from '@vue/runtime-test'
 import {
   ITERATE_KEY,
   DebuggerEvent,
@@ -484,6 +484,37 @@ describe('api: watch', () => {
     expect(calls).toEqual(['render', 'watcher 1', 'watcher 2', 'render'])
   })
 
+  // #1852
+  it('flush: post watcher should fire after template refs updated', async () => {
+    const toggle = ref(false)
+    let dom: TestElement | null = null
+
+    const App = {
+      setup() {
+        const domRef = ref<TestElement | null>(null)
+
+        watch(
+          toggle,
+          () => {
+            dom = domRef.value
+          },
+          { flush: 'post' }
+        )
+
+        return () => {
+          return toggle.value ? h('p', { ref: domRef }) : null
+        }
+      }
+    }
+
+    render(h(App), nodeOps.createElement('div'))
+    expect(dom).toBe(null)
+
+    toggle.value = true
+    await nextTick()
+    expect(dom!.tag).toBe('p')
+  })
+
   it('deep', async () => {
     const state = reactive({
       nested: {

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

@@ -403,6 +403,22 @@ describe('scheduler', () => {
     expect(calls).toEqual(['job3', 'job2', 'job1'])
   })
 
+  test('sort SchedulerCbs based on id', async () => {
+    const calls: string[] = []
+    const cb1 = () => calls.push('cb1')
+    // cb1 has no id
+    const cb2 = () => calls.push('cb2')
+    cb2.id = 2
+    const cb3 = () => calls.push('cb3')
+    cb3.id = 1
+
+    queuePostFlushCb(cb1)
+    queuePostFlushCb(cb2)
+    queuePostFlushCb(cb3)
+    await nextTick()
+    expect(calls).toEqual(['cb3', 'cb2', 'cb1'])
+  })
+
   // #1595
   test('avoid duplicate postFlushCb invocation', async () => {
     const calls: string[] = []

packages/runtime-core/src/renderer.ts

@@ -42,7 +42,8 @@ import {
   flushPostFlushCbs,
   invalidateJob,
   flushPreFlushCbs,
-  SchedulerJob
+  SchedulerJob,
+  SchedulerCb
 } from './scheduler'
 import { effect, stop, ReactiveEffectOptions, isRef } from '@vue/reactivity'
 import { updateProps } from './componentProps'
@@ -330,17 +331,20 @@ export const setRef = (
     // null values means this is unmount and it should not overwrite another
     // ref with the same key
     if (value) {
+      ;(doSet as SchedulerCb).id = -1
       queuePostRenderEffect(doSet, parentSuspense)
     } else {
       doSet()
     }
   } else if (isRef(ref)) {
+    const doSet = () => {
+      ref.value = value
+    }
     if (value) {
-      queuePostRenderEffect(() => {
-        ref.value = value
-      }, parentSuspense)
+      ;(doSet as SchedulerCb).id = -1
+      queuePostRenderEffect(doSet, parentSuspense)
     } else {
-      ref.value = value
+      doSet()
     }
   } else if (isFunction(ref)) {
     callWithErrorHandling(ref, parentComponent, ErrorCodes.FUNCTION_REF, [

packages/runtime-core/src/scheduler.ts

@@ -22,18 +22,21 @@ export interface SchedulerJob {
   allowRecurse?: boolean
 }
 
+export type SchedulerCb = Function & { id?: number }
+export type SchedulerCbs = SchedulerCb | SchedulerCb[]
+
 let isFlushing = false
 let isFlushPending = false
 
 const queue: (SchedulerJob | null)[] = []
 let flushIndex = 0
 
-const pendingPreFlushCbs: Function[] = []
-let activePreFlushCbs: Function[] | null = null
+const pendingPreFlushCbs: SchedulerCb[] = []
+let activePreFlushCbs: SchedulerCb[] | null = null
 let preFlushIndex = 0
 
-const pendingPostFlushCbs: Function[] = []
-let activePostFlushCbs: Function[] | null = null
+const pendingPostFlushCbs: SchedulerCb[] = []
+let activePostFlushCbs: SchedulerCb[] | null = null
 let postFlushIndex = 0
 
 const resolvedPromise: Promise<any> = Promise.resolve()
@@ -42,7 +45,7 @@ let currentFlushPromise: Promise<void> | null = null
 let currentPreFlushParentJob: SchedulerJob | null = null
 
 const RECURSION_LIMIT = 100
-type CountMap = Map<SchedulerJob | Function, number>
+type CountMap = Map<SchedulerJob | SchedulerCb, number>
 
 export function nextTick(fn?: () => void): Promise<void> {
   const p = currentFlushPromise || resolvedPromise
@@ -84,9 +87,9 @@ export function invalidateJob(job: SchedulerJob) {
 }
 
 function queueCb(
-  cb: Function | Function[],
-  activeQueue: Function[] | null,
-  pendingQueue: Function[],
+  cb: SchedulerCbs,
+  activeQueue: SchedulerCb[] | null,
+  pendingQueue: SchedulerCb[],
   index: number
 ) {
   if (!isArray(cb)) {
@@ -108,11 +111,11 @@ function queueCb(
   queueFlush()
 }
 
-export function queuePreFlushCb(cb: Function) {
+export function queuePreFlushCb(cb: SchedulerCb) {
   queueCb(cb, activePreFlushCbs, pendingPreFlushCbs, preFlushIndex)
 }
 
-export function queuePostFlushCb(cb: Function | Function[]) {
+export function queuePostFlushCb(cb: SchedulerCbs) {
   queueCb(cb, activePostFlushCbs, pendingPostFlushCbs, postFlushIndex)
 }
 
@@ -152,6 +155,9 @@ export function flushPostFlushCbs(seen?: CountMap) {
     if (__DEV__) {
       seen = seen || new Map()
     }
+
+    activePostFlushCbs.sort((a, b) => getId(a) - getId(b))
+
     for (
       postFlushIndex = 0;
       postFlushIndex < activePostFlushCbs.length;
@@ -167,7 +173,8 @@ export function flushPostFlushCbs(seen?: CountMap) {
   }
 }
 
-const getId = (job: SchedulerJob) => (job.id == null ? Infinity : job.id)
+const getId = (job: SchedulerJob | SchedulerCb) =>
+  job.id == null ? Infinity : job.id
 
 function flushJobs(seen?: CountMap) {
   isFlushPending = false
@@ -215,7 +222,7 @@ function flushJobs(seen?: CountMap) {
   }
 }
 
-function checkRecursiveUpdates(seen: CountMap, fn: SchedulerJob | Function) {
+function checkRecursiveUpdates(seen: CountMap, fn: SchedulerJob | SchedulerCb) {
   if (!seen.has(fn)) {
     seen.set(fn, 1)
   } else {