Previously, under certain circumstances, `NgZone#onMicrotaskEmpty` could
emit while a `$digest` was in progress, thus triggering another
`$digest`, which in turn would throw a `$digest already in progress`
error. Furthermore, throwing an error from inside the `onMicrotaskEmpty`
subscription would result in unsubscribing and stop triggering further
`$digest`s, when `onMicrotaskEmpty` emitted.
Usually, emitting while a `$digest` was already in progress was a result
of unintentionally running some part of AngularJS outside the Angular
zone, but there are valid (if rare) usecases where this can happen
(see #24680 for details).
This commit addresses the issue as follows:
- If a `$digest` is in progress when `onMicrotaskEmpty` emits, do not
trigger another `$digest` (to avoid the error). `$evalAsync()` is used
instead, to ensure that the bindings are evaluated at least once more.
- Since there is still a high probability that the situation is a result
of programming error (i.e. some AngularJS part running outside the
Angular Zone), a warning will be logged, but only if the app is in
[dev mode][1].
[1]: https://github.com/angular/angular/blob/78146c189/packages/core/src/util/ng_dev_mode.ts#L12Fixes#24680
PR Close#29794
0ddf2e7a5b