Property wrappers without parenthesis

Using Swift
1

Hi!

I've just discovered that if property wrapper has generic parameters other than wrappedValue's type and it has initialiser without arguments under some constraint, you can't use this property wrapper without parenthesis:

enum First {}

@propertyWrapper
struct MagicBox<T, Mode> {
  var wrappedValue: T

  init() where Mode == First {
    fatalError()
  }
}

// Error: Generic parameter 'Mode' could not be inferred
@MagicBox
var foo: Int 

// Works fine
@MagicBox()
var foo: Int

So, as I understand, compiler has enough information to infer Mode parameter, but it can't for some reason. Is that expected behaviour or bug? May be I'm missing something?

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