Issue Description:

Unhelpful error points to wrong argument.

I get the error:

cannot convert value of type '[Int]' to expected argument type '[_]'
let d = Broken<Int>(items: numbers, block: {  })
                           ^~~~~~~

With the following code when the error is the block is incorrect closure for one with arguments.

class Broken<T> {
    init(items:[T],
    block:(Int)->Void) {
    }
}
let numbers = [1,2,3,4]

let d = Broken<Int>(items: numbers, block: {  })

If the case above the error can be fixed by changing the closure to `{ _ in }`

In some more complicated cases I have found an explicit return is needed in a closure that returns Void. I don't have that well minimised at this point though.