fix https://github.com/angular/components/issues/21674
When setting `ngZoneRunCoalescing` to true, `onStable` is not emitted correctly.
the reason is before this commit, the code looks like this:
```
// application code call `ngZone.run()`
ngzone.run(() => {}); // step 1
// inside NgZone, in the OnInvoke hook, NgZone try to delay the checkStable()
function delayChangeDetectionForEvents(zone: NgZonePrivate) {
if (zone.lastRequestAnimationFrameId !== -1) { // step 9
return;
}
zone.lastRequestAnimationFrameId = zone.nativeRequestAnimationFrame.call(global, () => { // step 2
if (!zone.fakeTopEventTask) {
zone.fakeTopEventTask = Zone.root.scheduleEventTask('fakeTopEventTask', () => {
zone.lastRequestAnimationFrameId = -1; // step 3
updateMicroTaskStatus(zone); // step 4
checkStable(zone); // step 6
}, undefined, () => {}, () => {});
}
zone.fakeTopEventTask.invoke();
});
updatemicroTaskStatus(zone);
}
function updateMicroTaskStatus(zone: NgZonePrivate, ignoreCheckRAFId = false) {
if (zone._hasPendingMicrotasks ||
((zone.shouldCoalesceEventChangeDetection || zone.shouldCoalesceRunChangeDetection) &&
zone.lastRequestAnimationFrameId !== -1)) { // step 5
zone.hasPendingMicrotasks = true;
} else {
zone.hasPendingMicrotasks = false;
}
}
function checkStable(zone: NgZonePrivate) {
if (zone._nesting == 0 && !zone.hasPendingMicrotasks && !zone.isStable) { // step 7
try {
zone._nesting++;
zone.onMicrotaskEmpty.emit(null);
...
}
// application ref subscribe onMicroTaskEmpty
ngzone.onMicroTaskEmpty.subscribe(() => {
ngzone.run(() => { // step 8
tick();
});
});
```
and the process is:
1. step 1: application call ngZone.run()
2. step 2: NgZone delay the checkStable() call in a requestAnimationFrame, and also set
zone.lastRequestAnimationFrameId
3. step 3: Inside the requestAnimationFrame callback, reset zone.lastRequestAnimationFrameId first
4. step 4: update microTask status
5, step 5: if zone.lastRequestAnimationFrameId is -1, that means no microTask pending.
6. step 6: checkStable and trigger onMicrotaskEmpty emitter.
7. step 7: ApplicationRef subscribed onMicrotaskEmpty, so it will call another `ngZone.run()` to process
tick()
8. step 8: And this new `ngZone.run()` will try to check `zone.lastRequestAnimationFrameId` in `step 9`
when trying to delay the checkStable(), and since the zone.lastRequestAnimationFrameId is already reset
to -1 in step 3, so this ngZone.run() will run into step 2 again.
9. and become a infinite loop..., so onStable is never emit
in this commit, there is a new flag `zone.isCheckStableRunning` added to
prevent re-entry when `shouldCoaleascing` flag is enabled.
PR Close#40540
dc9fd1aaef