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Update SE-0192 for Swift 6 language mode #2450

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Update SE-0192 for Swift 6 language mode #2450

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3 changes: 3 additions & 0 deletions proposals/0192-non-exhaustive-enums.md
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Expand Up @@ -4,6 +4,7 @@
* Author: [Jordan Rose](https://github.com/jrose-apple)
* Review Manager: [Ted Kremenek](https://github.com/tkremenek)
* Status: **Implemented (Swift 5.0)**
* Upcoming Feature Flag: `NonfrozenEnumExhaustivity` (implemented in Swift 6.0 to subsume bespoke compiler flag for Swift 4/4.2 language mode)
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@dempseyatgithub dempseyatgithub May 16, 2024 •
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Suggested change
* Upcoming Feature Flag: `NonfrozenEnumExhaustivity` (implemented in Swift 6.0 to subsume bespoke compiler flag for Swift 4/4.2 language mode)
* Upcoming Feature Flag: `NonfrozenEnumExhaustivity` (implemented in Swift 6.0) (enabled in Swift 6 language mode)

This should also include the (enabled in Swift 6 language mode) annotation to indicate when the flag is always enabled.

The details of what an upcoming feature flag does is not included as part of the header field. The details should be generally be included in the "Source Compatibility" section or elsewhere in the proposal. In this case, in the introduction.

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@xwu xwu May 16, 2024 •
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This is tricky to explain. It is enabled in Swift 5 language mode too; the flag has no effect except in Swift 4/4.2 mode.

* Implementation: [apple/swift#14945](https://github.com/apple/swift/pull/14945)
* Previous revision: [1](https://github.com/apple/swift-evolution/blob/a773d07ff4beab8b7855adf0ac56d1e13bb7b44c/proposals/0192-non-exhaustive-enums.md), [2 (informal)](https://github.com/jrose-apple/swift-evolution/blob/57dfa2408fe210ed1d5a1251f331045b988ee2f0/proposals/0192-non-exhaustive-enums.md), [3](https://github.com/apple/swift-evolution/blob/af284b519443d3d985f77cc366005ea908e2af59/proposals/0192-non-exhaustive-enums.md)
* Pre-review discussion: [Enums and Source Compatibility](https://forums.swift.org/t/enums-and-source-compatibility/6460), with additional [orphaned thread](https://forums.swift.org/t/enums-and-source-compatibility/6651)
Expand All @@ -21,6 +22,8 @@ A key note: in this version of the proposal, *nothing changes for user-defined S

- Since the proposal was accepted months after it was written, the rollout plan turned out to be a little too aggressive. Therefore, in Swift 5 the diagnostic for omitting `@unknown default:` or `@unknown case _:` will only be a warning, and in Swift 4 mode there will be no diagnostic at all. (The previous version of the proposal used an error and a warning, respectively.) Developers are still free to use `@unknown` in Swift 4 mode, in which case the compiler will still produce a warning if all known cases are not handled.

- To complete the rollout of this feature, the warning is [upgraded to an error for the Swift 6 language mode](https://forums.swift.org/t/amendment-se-0192-handling-future-enum-cases/68321)

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The upcoming feature flag `NonfrozenEnumExhaustivity` is implemented in Swift 6.0 to subsume the bespoke compiler flag for Swift 4/4.2 language mode.


### Revision at acceptance

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