       }
       // Non-ASCII, proceed to buffering mode.
       buffer.append(codeUnit)
-    } else if Encoding._isScalar(Encoding.CodeUnit(extendingOrTruncating: buffer._storage)) {
+    } else if Encoding._isScalar(
+      Encoding.CodeUnit(extendingOrTruncating: buffer._storage)
+    ) {
       // ASCII in buffer.  We don't refill the buffer so we can return
       // to bufferless mode once we've exhausted it.
       let codeUnit = Encoding.CodeUnit(extendingOrTruncating: buffer._storage)

  }
}

extension
 Unicode.UTF8.ForwardDecoder : _UTFDecoder {
  public typealias Encoding = Unicode.UTF8
  
  public // @testable

  func _bufferedScalar(bitCount: UInt8) -> Encoding.EncodedScalar
}

extension _UTFDecoder
where Encoding.EncodedScalar == _UIntBuffer<UInt32, Encoding.CodeUnit> {
  public mutating func parseScalar<I : IteratorProtocol>(
    from input: inout I
  ) -> Unicode.ParseResult<Encoding.EncodedScalar>
