ensure _futurize does not leak uncaught errors into the zone #32070
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Gold has detected about 5 new digest(s) on patchset 2. |
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Gold has detected about 18 new digest(s) on patchset 3. |
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Gold has detected about 18 new digest(s) on patchset 4. |
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I am ... extremely confused on how this is changing web goldens. |
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From discussion on discord, the web goldens are having issues unrelated and we just approve them for now |
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| test('_futureize does not leak sync uncaught exceptions into the zone', () async { |
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If we're going through the trouble of maintaining an additional copy of _futurize, we should try to get more than one unit test out of the bargain. This test covers one of three error pathways, and there is also the success pathway, as examples.
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Gold has detected about 18 new digest(s) on patchset 7. |
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Do I need to do anything else to satisfy the gold bot? |
No, you're good. |
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* 7fe613a Roll Dart SDK from 5bc905e69609 to ad5a250935d5 (4 revisions) (flutter/engine#32079) * 3a954ba Disable several tests due to flakiness (flutter/engine#32059) * 05bba9b [web] Log all goldctl commands (flutter/engine#32072) * 86b2c8d Roll Skia from 9301fe3779bb to 02ebd1a23381 (4 revisions) (flutter/engine#32067) * abb1bce Roll Fuchsia Linux SDK from mVqiTwaVa... to RAyopISUl... (flutter/engine#32069) * 481f4bc Roll Fuchsia Mac SDK from vWlaMIVkM... to -JEG0j8mn... (flutter/engine#32077) * 560243c Roll Dart SDK from ad5a250935d5 to 5168cdd236a0 (1 revision) (flutter/engine#32081) * e2e6b49 Roll Skia from 02ebd1a23381 to 5e035c66da3c (19 revisions) (flutter/engine#32082) * e4056c5 ensure _futurize does not leak uncaught errors into the zone (flutter/engine#32070)
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Because this is a private function, and because I don't see any tests that use the part of trick to test private functions, I cheated a bit by creating a copy.
Explanation:
When you add an error to a completer, the completer first checks if it has a listener or not. if there is a listener (either from the future or from async/await) then the error is forwarded there. If there is no listener then the error is forwarded to the current Zone's uncaught exception handler.
sync Completers and async Completers work the same in this regard, but async completers always check for a listener in a later microtask whereas a sync Completer will check as soon as it is completed. This means that for a function which immediately/synchronously errors, the Completer may check for a listener before the function has returned - and before the caller has had a chance to add a listener
To fix this, we check in the body of the callback if the function has progressed passed the callback invocation. If it has not, then we know the caller has not added a listener yet and we must synchronously throw an error. If we have passed the body, then the caller will have already added a listener and we can forward the error to the Completer
For a demonstration see https://dartpad.dev/?id=eebd0a2bba7d88d0e9969a68b4bc4a59