Open Radar

 
Summary:
Foundation's range(of:options:) doesn't support Swift 4's Substring type. The range returned is calculated in the original string, not the substring.

Steps to Reproduce:
Run the following code on macOS (in a Playground or via the command line):

```swift
import Foundation

let str = "Yo Hello, playground"
let start = str.index(str.startIndex, offsetBy: 3)
let substr = str[start...]

if let commaSpaceEnd = substr.range(of: ", ", options: .backwards)?.upperBound {
    print(substr[commaSpaceEnd...])
}

if let commaSpaceEnd = str.range(of: ", ", options: .backwards)?.upperBound {
    print(str[commaSpaceEnd...])
}
```

Expected Results:
Should print:

playground
playground

Actual Results:
Actually prints:

o, playground
playground

Version:
Xcode 9 beta 5 (9M202q)

Notes: