Open Radar

 
I have a TokenizerType defined:

public protocol TokenizerType {
    typealias ContentType
    typealias ContentIndexType : ForwardIndexType
    
    var rules: [(content: ContentType, offset: ContentIndexType) -> ContentIndexType?] { get }
    var content: ContentType { get }

    init(content: ContentType)
    
    func next(index: ContentIndexType?) throws -> TokenizerResult<ContentType, ContentIndexType>?
}

It also has an extension to the protocol in that same module for the next() function:

extension TokenizerType where ContentType == String, ContentIndexType == String.Index {
    public func next(index: String.Index?) throws -> TokenizerResult<String, String.Index>? { … }
}

Now, when I define a new type, it fails when nested within a function it fails to compile:

func f() {
   struct EmptyTokenizer : TokenizerType {
       
       let rules: [(content: String, offset: String.Index) -> String.Index?] = []
       let content: String
       
       init(content: String) {
           self.content = content
       }
       
       func next(index: String.Index?) throws -> TokenizerResult<String, String.Index>? {
           return nil
       }
   }
}

Promoting the struct to global scope works. This seems like a bug.