6.0: [BitwiseCopyable] Avoid a condfail. #73538
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Rather than immediately outright banning the old protocol, just make it be a deprecated typealias for the real one.
The standard library defines
```
protocol BitwiseCopyable {}
typealias _BitwiseCopyable = BitwiseCopyable
```
For current compilers, `BitwiseCopyable` is a "known protocol".
For older compilers, it is not; instead `_BitwiseCopyable` is. So
print the following into the swiftinterface for those older compilers:
```
protocol _BitwiseCopyable {}
typealias BitwiseCopyable = _BitwiseCopyable
```
rdar://127755503
|
@swift-ci please test |
|
Thank you for fixing the condfail issue, Nate! |
tbkka
approved these changes
May 9, 2024
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Explanation: Fix a condfail related to BitwiseCopyable renaming.
Once the evolution proposal was accepted, the protocol was renamed from
_BitwiseCopyabletoBitwiseCopyable. Old compilers still only "know about"_BitwiseCopyable, however--it is a "known protocol" for them. They only permit suppression of_BitwiseCopyableand notBitwiseCopyable. This is a problem for the new standard library's swiftinterface which includes several suppressions ofBitwiseCopyable.The solution is to keep defining the
_BitwiseCopyableprotocol in the standard library's swiftinterface as understood by older compilers while definingBitwiseCopyableto be a typealias for it. Meanwhile, when current compilers read the same swiftinterface, they will seeBitwiseCopyableto be defined as a protocol and_BitwiseCopyableto be a typealias for it.Scope: Affects ASTPrinting of the BitwiseCopyable protocol and its deprecated typealias.
Issue: rdar://127755503
Original PR: #73516
Risk: Very low. Only affects ASTPrinting of two declarations.
Testing: Added tests.
Reviewer: Allan Shortlidge ( @tshortli )