callAsFunction + rethrows is broken.

[JessyCatterwaul]

I don't remember if it ever worked. Paul Hudson's article says it did/should.

struct Struct {
  typealias Closure = () throws -> Void
  func ƒ(_: Closure) rethrows { }
  func callAsFunction(_: Closure) rethrows { }
}

Struct().ƒ { }
Struct() { } // Call can throw but is not marked with 'try'

[JessyCatterwaul]

While this is still broken in Swift 6, it doesn't really matter, because you can completely get around it using the new solution.

struct Struct {
  typealias Closure<Error> = () throws(Error) -> Void
  func ƒ(_: Closure<Error>) { }
  func callAsFunction(_: Closure<some Error>) { }
}

Struct().ƒ { }
Struct() { } // Compiles.

There are still some issues, e.g. #74273, but maybe rethrows should just be deprecated.