Swift 6.1: Trailing commas are not allowed in generic lists

[dfed]

The following trailing comma causes a compiler error on Xcode 16.3.0 in Swift 6.1:

public final class TestThing: GenericThing<
	Test1,
	Test2,
	Test3,
> { }

[ivan-gaydamakin]

public typealias CreditCardTopUpMethod = BalanceTopUpAvailableMethodTransfer.TopUpMethod<
    BalanceTopUpDisabledCreditCardMethodReason,
>
public typealias BankTopUpMethod = BalanceTopUpAvailableMethodTransfer.TopUpMethod<
    BalanceTopUpDisabledBankMethodReason,
>


func issue() -> Result<
    String, Error,
> {}

Same issue in typealias and functions

UPD:
Also applied for @available :/

// Deprecated typealiases
@available(
    *,
    deprecated,
    renamed: "FontConvertible.Font",
    message: "This typealias will be removed in SwiftGen 7.0",
)

[calda]

Delightfully, it does work in cases like:

struct Foo<
  T1,
  T2,
  T3, // trailing comma allowed
> { }

Seems like it should be supported. Reported in swiftlang/swift#81474. Of course we'll have to work around the Swift 6.1 issue in SwiftFormat.

Same for @available: swiftlang/swift#81475

[calda]

Here's the fix: #2047

[calda]

Fixed in 0.56.1: https://github.com/nicklockwood/SwiftFormat/releases/tag/0.56.1

[calda]

Compiler fix: swiftlang/swift#81612

Hopefully we can get this into Swift 6.2

[calda]

Fixed for Swift 6.2 👍 swiftlang/swift#81653

I'll make sure to update the format rule to handle the updated Swift 6.2 behavior once an Xcode beta with it is out.

[calda]

Trailing commas not being supported in built-in attributes like @available turned out to be expected behavior.