Merge pull request #1130 from apple/swift-PR-11088

Author: swift-ci

Foundation/NSString.swift

@@ -346,49 +346,7 @@ extension NSString {
             let start = _storage.utf16.startIndex
             let min = start.advanced(by: range.location)
             let max = start.advanced(by: range.location + range.length)
-            if let substr = String(_storage.utf16[min..<max]) {
-                return substr
-            }
-            //If we come here, then the range has created unpaired surrogates on either end.
-            //An unpaired surrogate is replaced by OXFFFD - the Unicode Replacement Character.
-            //The CRLF ("\r\n") sequence is also treated like a surrogate pair, but its constinuent
-            //characters "\r" and "\n" can exist outside the pair!
-
-            let replacementCharacter = String(describing: UnicodeScalar(0xFFFD)!)
-            let CR: UInt16 = 13  //carriage return
-            let LF: UInt16 = 10  //new line
-
-            //make sure the range is of non-zero length
-            guard range.length > 0 else { return "" }
-
-            //if the range is pointing to a single unpaired surrogate
-            if range.length == 1 {
-                switch _storage.utf16[min] {
-                case CR: return "\r"
-                case LF: return "\n"
-                default: return replacementCharacter
-                }
-            }
-
-            //set the prefix and suffix characters
-            let prefix = _storage.utf16[min] == LF ? "\n" : replacementCharacter
-            let suffix = _storage.utf16[max.advanced(by: -1)] == CR ? "\r" : replacementCharacter
-
-            //if the range breaks a surrogate pair at the beginning of the string
-            if let substrSuffix = String(_storage.utf16[min.advanced(by: 1)..<max]) {
-                return prefix + substrSuffix
-            }
-
-            //if the range breaks a surrogate pair at the end of the string
-            if let substrPrefix = String(_storage.utf16[min..<max.advanced(by: -1)]) {
-                return substrPrefix + suffix
-            }
-
-            //the range probably breaks surrogate pairs at both the ends
-            guard min.advanced(by: 1) <= max.advanced(by: -1) else { return prefix + suffix }
-
-            let substr =  String(_storage.utf16[min.advanced(by: 1)..<max.advanced(by: -1)])!
-            return prefix + substr + suffix
+            return String(decoding: _storage.utf16[min..<max], as: UTF16.self)
         } else {
             let buff = UnsafeMutablePointer<unichar>.allocate(capacity: range.length)
             getCharacters(buff, range: range)