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4c990dc0b9
Allow `AsyncSequence.flatMap` to be defined with "incorrect" availability, meaning that the function can refer to the `Failure` associated type in its where clause even though the function is back-deployed to before the `Failure` associated type was introduced. We believe this is safe, and that this notion can be generalized to any use of an associated type in a same-type constraint of a function (yes, it sounds weird), but for now introduce a narrower hack to see how things work in practice and whether it addresses all of the source-compatibility concerns we've uncovered.
22 lines
572 B
Swift
22 lines
572 B
Swift
// RUN: %target-swift-frontend -typecheck %s -verify
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// REQUIRES: concurrency
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@available(SwiftStdlib 5.1, *)
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struct MyAsyncSequence<Element>: AsyncSequence {
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struct AsyncIterator: AsyncIteratorProtocol {
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mutating func next() -> Element? { nil }
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}
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func makeAsyncIterator() -> AsyncIterator { .init() }
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}
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@available(SwiftStdlib 5.1, *)
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func testMe(ms: MyAsyncSequence<String>) {
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let flatMS = ms.flatMap { string in
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return MyAsyncSequence<[Character]>()
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}
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let _: AsyncFlatMapSequence<MyAsyncSequence<String>, MyAsyncSequence<[Character]>> = flatMS
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}
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