[Conformance checking] Better handling of escaping function types #15350
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…pe ones. When inferring an associated type witness by matching a function signature, adjust non-escaping function types to escaping function types, because only escaping function types could be written as explicit witnesses and non-escaping function types are not permitted outside of function parameters. Addresses the first part of rdar://problem/35297911, eliminating the type-soundness issue.
…g parameter Extend protocol conformance checking to allow a requirement with an escaping parameter (of function type) to be satisfied by a witness with a corresponding non-escaping parameter. This limited form of covariance was already supported by SILGen and is needed to address the source-compatibility "regression" introduced by inferring escaping function types for associated type witnesses. It's also obviously a good idea :) Fixes rdar://problem/35297911.
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@swift-ci please smoke test and merge |
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@swift-ci please smoke test and merge |
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Improve our handling of (non-)escaping function types in conformance checking in two ways to tighten up type soundness:
noescapefunction type, adjust the function type to be escaping. This addresses a type soundness issue, where values of non-escaping function type could arbitrarily escape through type witnesses.noescapefunction type match a requirement with a compatible escaping function type. While this limited form of witness covariance is generally a good idea, it is also necessary because closing the type soundness hole describe above would break some existing code.Fixes rdar://problem/35297911