Check and emit fixes for async iteration #15277
Merged
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This changes the emit for the
__asyncGeneratorand__asyncDelegatorhelpers to fix issues withyield*delegation in an async generator. The main change involves modifying__asyncDelegatorto use a two-phase approach to iteration:next/throw/returnto__asyncGeneratoras if it were anawaitand switch phase. After awaiting the result,__asyncGeneratorsends it back to the delegator via a call to itsnextmethod.__asyncGeneratoreither as ayieldor areturnand switch phase.This also addresses a bug in the checker and correctly emits
__asyncValuesin some cases where it was missing.This also addresses an issue where a Promise rejection during delegation of an async iterator was not properly handled.
Fixes: #15143, #14725, and #14442
Related: microsoft/tslib#29