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Before Null Safety, `_EventStreamSubscription.cancel()` used a trick to run with synchronous timing even though it was typed to return a `Future`. During the migration of the SDK to support Null Safety it kept the synchronous timing in weak mode, but was changed to asynchronous in sound mode so that the behavior matched the method signature. In hindsight, changing the timing when opting into Null Safety is problematic: * A shared package has no control over what mode it runs in. Libraries may be opted in and run their tests with sound null safety but the apps they are used in could still be running in weak mode. This results in library unit tests that behave differently than the production app that deploys the code. * This codepath can be triggered by EventTarget.dispatchEvent() from dart:html which should have synchronous timings for the event listeners before returning to the calling code. The asynchronous timing when running with sound null safety is inconsistent with the browser API. This change reverses that migration decision and keeps the synchronous timing in both modes. To support this in sound mode it returns a special future value that is internal to the SDK and known to be used for synchronous timing. This change also removes the workaround introduced in DDC to avoid warning/failing when `_EventStreamSubscription.cancel()` returned null and the extra warnings/errors features were enabled in weak null safety mode. Change-Id: I6b08a2ada5b10120bea787ad59d1d58e6e181de5 Fixes: https://github.com/dart-lang/sdk/issues/44157 Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/175323 Commit-Queue: Nicholas Shahan <nshahan@google.com> Reviewed-by: Srujan Gaddam <srujzs@google.com> Reviewed-by: Sigmund Cherem <sigmund@google.com> |
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