`JSONEncoder.OutputFormatting.sortedKeys` behavior differs between Darwin and non-Darwin implementation

[fumoboy007]

The behavior of JSONEncoder.OutputFormatting.sortedKeys differs between the Darwin and non-Darwin implementation of Foundation.

A developer may rely on this formatting option to make a test deterministic. However, because the behavior differs across platforms, the test is not portable.

Test Case

import Foundation

let dictionary = [
  "a": "a",
  "B": "b"
]

let jsonEncoder = JSONEncoder()
jsonEncoder.outputFormatting = [.sortedKeys]

let jsonBytes = try! jsonEncoder.encode(dictionary)
let jsonString = String(decoding: jsonBytes, as: UTF8.self)

print(jsonString)

Darwin Output

{"a":"a","B":"b"}

Non-Darwin Output

{"B":"b","a":"a"}