Merge pull request #10350 from inamiy/CodingKey-CustomStringConvertible

Let CodingKey inherit CustomStringConvertible for better debugging

Author: itaiferber

stdlib/public/core/Codable.swift

@@ -47,7 +47,7 @@ public typealias Codable = Encodable & Decodable
 //===----------------------------------------------------------------------===//
 
 /// A type that can be used as a key for encoding and decoding.
-public protocol CodingKey {
+public protocol CodingKey: CustomStringConvertible, CustomDebugStringConvertible {
     /// The string to use in a named collection (e.g. a string-keyed dictionary).
     var stringValue: String { get }
 
@@ -67,6 +67,19 @@ public protocol CodingKey {
     init?(intValue: Int)
 }
 
+extension CodingKey {
+    /// A textual representation of this key.
+    public var description: String {
+        let intValue = self.intValue?.description ?? "nil"
+        return "\(type(of: self))(stringValue: \"\(stringValue)\", intValue: \(intValue))"
+    }
+
+    /// A textual representation of this key, suitable for debugging.
+    public var debugDescription: String {
+        return description
+    }
+}
+
 //===----------------------------------------------------------------------===//
 // Encoder & Decoder
 //===----------------------------------------------------------------------===//