fix(core): Microtask scheduling should be used after any application synchronization#65885
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AndrewKushnir merged 1 commit intoangular:mainfrom Dec 16, 2025
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…synchronization Previously, Angular would switch from the macrotask to a microtask scheduler _only_ when the scheduler was the trigger for the synchronization. This microtask scheduling is to ensure patterns such as `Promise.resolve().then(() => updateAppStateAgain())` _during_ synchronization are caught and synchronized again within the same event loop (guaranteeing that they aren't split across multiple browser paints). The microtask scheduler should be used after any tick, not just from those than run within the scheduler to always account for the promises within synchronization. This is encountered most frequently during bootstrap, which triggers the tick directly. In this change we exempt `TestBed.tick` and `ComponentFixture.detectChanges` from this behavior. Doing so would affect the timing of stability and tests are quite sensitive to this (e.g. `fixture.whenStable`). It is somewhat unfortunate that we have "special" test-only behavior. However, it is important to acknowledge that this only affects the test-only APIs as well. Any code in the application under test that triggers `ApplicationRef.tick` directly would still use the microtask scheduling behavior. fixes angular#65444
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Previously, Angular would switch from the macrotask to a microtask scheduler only when the scheduler was the trigger for the synchronization. This microtask scheduling is to ensure patterns such as
Promise.resolve().then(() => updateAppStateAgain())during synchronization are caught and synchronized again within the same event loop (guaranteeing that they aren't split across multiple browser paints).The microtask scheduler should be used after any tick, not just from those than run within the scheduler to always account for the promises within synchronization. This is encountered most frequently during bootstrap, which triggers the tick directly.
In this change we exempt
TestBed.tickandComponentFixture.detectChangesfrom this behavior. Doing so would affect the timing of stability and tests are quite sensitive to this (e.g.fixture.whenStable). It is somewhat unfortunate that we have "special" test-only behavior. However, it is important to acknowledge that this only affects the test-only APIs as well. Any code in the application under test that triggersApplicationRef.tickdirectly would still use the microtask scheduling behavior.fixes #65444