[Associated type inference] Limit Failure inference to rethrows next()
#71494
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When inferring a type witness for `AsyncIteratorProtocol` or `AsyncSequence`'s `Failure` associated type, don't infer from a generic parameter named `Failure`. Instead, use `next()` as a cue: if it `rethrows`, use `Failure` from one of the conformances; if it `throws`, use `any Error`. This is a more conservative inference rule, and addresses a failure to infer a `Failure` type witness for some fairly-obvious cases. Fixes rdar://122514816.
DougGregor
requested review from
ktoso,
hborla,
slavapestov and
xedin
as code owners
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@swift-ci please smoke test |
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@swift-ci please test source compatibility |
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When inferring a type witness for
AsyncIteratorProtocolorAsyncSequence'sFailureassociated type, don't infer from a generic parameter namedFailure. Instead, usenext()as a cue: if itrethrows, useFailurefrom one of the conformances; if itthrows, useany Error. This is a more conservative inference rule, and addresses a failure to infer aFailuretype witness for some fairly-obvious cases.Fixes rdar://122514816.