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Allan Shortlidge
233906cd57
When checking conformances, if the witness to a protocol requirement is the default witness for that requirement, ignore MemberImportVisibility restrictions. A default witness is the witness that will be used at runtime for a conformance to a resilient protocol when the conformance does not provide its own witness. Default witnesses must belong to an unconstrained extension of the protocol and be declared in the same module as that protocol. This exception is necessary because otherwise evolving a protocol by adding a new requirement with a default witness is potentially source breaking, even though it would not be ABI breaking. Resolves https://github.com/swiftlang/swift/issues/87227 and rdar://170348842.