Add JSON and property list encoders and decoders

* Integrate {JSON,PropertyList}{Encoder,Decoder} types to facilitate
  encoding types in JSON and property list formats
* Adds Foundation-specific extensions to allow errors exposed from the
  stdlib to bridge to NSErrors

Author: Itai Ferber

stdlib/public/SDK/Foundation/CMakeLists.txt

@@ -6,6 +6,7 @@ add_swift_library(swiftFoundation ${SWIFT_SDK_OVERLAY_LIBRARY_BUILD_TYPES} IS_SD
   Boxing.swift
   Calendar.swift
   CharacterSet.swift
+  Codable.swift
   Data.swift
   DataThunks.m
   Date.swift
@@ -17,6 +18,7 @@ add_swift_library(swiftFoundation ${SWIFT_SDK_OVERLAY_LIBRARY_BUILD_TYPES} IS_SD
   Foundation.swift
   IndexPath.swift
   IndexSet.swift
+  JSONEncoder.swift
   Locale.swift
   Measurement.swift
   Notification.swift
@@ -41,6 +43,7 @@ add_swift_library(swiftFoundation ${SWIFT_SDK_OVERLAY_LIBRARY_BUILD_TYPES} IS_SD
   NSURL.swift
   NSValue.swift.gyb
   PersonNameComponents.swift
+  PlistEncoder.swift
   ReferenceConvertible.swift
   String.swift
   TimeZone.swift

stdlib/public/SDK/Foundation/Codable.swift

@@ -0,0 +1,200 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+//===----------------------------------------------------------------------===//
+// Codable Extensions
+//===----------------------------------------------------------------------===//
+
+extension Date : Codable {
+    public init(from decoder: Decoder) throws {
+        let timestamp = try decoder.singleValueContainer().decode(Double.self)
+        self.init(timeIntervalSince1970: timestamp)
+    }
+
+    public func encode(to encoder: Encoder) throws {
+        var container = encoder.singleValueContainer()
+        try container.encode(self.timeIntervalSince1970)
+    }
+}
+
+extension Data : Codable {
+    private enum CodingKeys : Int, CodingKey {
+        case length
+        case bytes
+
+        // TODO: Remove these when derived conformance is merged.
+        var stringValue: String {
+            switch self {
+            case .length: return "length"
+            case .bytes: return "bytes"
+            }
+        }
+
+        init?(stringValue: String) {
+            switch stringValue {
+            case "length": self = .length
+            case "bytes": self = .bytes
+            default: return nil
+            }
+        }
+
+        var intValue: Int? {
+            return self.rawValue
+        }
+
+        init?(intValue: Int) {
+            switch intValue {
+            case 0: self = .length
+            case 1: self = .bytes
+            default: return nil
+            }
+        }
+    }
+
+    public init(from decoder: Decoder) throws {
+        let container = try decoder.container(keyedBy: CodingKeys.self)
+        let length = try container.decode(Int.self, forKey: .length)
+        guard length >= 0 else {
+            throw DecodingError.dataCorrupted(DecodingError.Context(codingPath: decoder.codingPath,
+                                                                    debugDescription: "Cannot decode a Data of negative length \(length)."))
+        }
+
+        var bytesContainer = try container.nestedUnkeyedContainer(forKey: .bytes)
+
+        self.init(capacity: length)
+        for i in 0 ..< length {
+            let byte = try bytesContainer.decode(UInt8.self)
+            self[i] = byte
+        }
+    }
+
+    public func encode(to encoder: Encoder) throws {
+        var container = encoder.container(keyedBy: CodingKeys.self)
+        try container.encode(self.count, forKey: .length)
+
+        var bytesContainer = container.nestedUnkeyedContainer(forKey: .bytes)
+
+        // Since enumerateBytes does not rethrow, we need to catch the error, stow it away, and rethrow if we stopped.
+        var caughtError: Error? = nil
+        self.enumerateBytes { (buffer: UnsafeBufferPointer<UInt8>, byteIndex: Data.Index, stop: inout Bool) in
+            do {
+                for byte in buffer {
+                    try bytesContainer.encode(byte)
+                }
+            } catch {
+                caughtError = error
+                stop = true
+            }
+        }
+
+        if let error = caughtError {
+            throw error
+        }
+    }
+}
+
+//===----------------------------------------------------------------------===//
+// Errors
+//===----------------------------------------------------------------------===//
+
+// Adding the following extensions to EncodingError and DecodingError allows them to bridge to NSErrors implicitly.
+
+fileprivate let NSCodingPathErrorKey = "NSCodingPath"
+fileprivate let NSDebugDescriptionErrorKey = "NSDebugDescription"
+
+extension EncodingError : CustomNSError {
+    public static var errorDomain: String = NSCocoaErrorDomain
+
+    public var errorCode: Int {
+        switch self {
+        case .invalidValue(_, _): return CocoaError.coderInvalidValue.rawValue
+        }
+    }
+
+    public var errorUserInfo: [String : Any] {
+        let context: Context
+        switch self {
+        case .invalidValue(_, let c): context = c
+        }
+
+        return [NSCodingPathErrorKey: context.codingPath,
+                NSDebugDescriptionErrorKey: context.debugDescription]
+    }
+}
+
+extension DecodingError : CustomNSError {
+    public static var errorDomain: String = NSCocoaErrorDomain
+
+    public var errorCode: Int {
+        switch self {
+        case .valueNotFound(_, _): fallthrough
+        case .keyNotFound(_, _):
+            return CocoaError._coderValueNotFound.rawValue
+
+        case .typeMismatch(_, _): fallthrough
+        case .dataCorrupted(_):
+            return CocoaError._coderReadCorrupt.rawValue
+        }
+    }
+
+    public var errorUserInfo: [String : Any]? {
+        let context: Context
+        switch self {
+        case .typeMismatch(_, let c): context = c
+        case .valueNotFound(_, let c): context = c
+        case .keyNotFound(_, let c): context = c
+        case .dataCorrupted(let c): context = c
+        }
+
+        return [NSCodingPathErrorKey: context.codingPath,
+                NSDebugDescriptionErrorKey: context.debugDescription]
+    }
+}
+
+//===----------------------------------------------------------------------===//
+// Error Utilities
+//===----------------------------------------------------------------------===//
+
+internal extension DecodingError {
+    /// Returns a `.typeMismatch` error describing the expected type.
+    ///
+    /// - parameter path: The path of `CodingKey`s taken to decode a value of this type.
+    /// - parameter expectation: The type expected to be encountered.
+    /// - parameter reality: The value that was encountered instead of the expected type.
+    /// - returns: A `DecodingError` with the appropriate path and debug description.
+    internal static func _typeMismatch(at path: [CodingKey?], expectation: Any.Type, reality: Any) -> DecodingError {
+        let description = "Expected to decode \(expectation) but found \(_typeDescription(of: reality)) instead."
+        return .typeMismatch(expectation, Context(codingPath: path, debugDescription: description))
+    }
+
+    /// Returns a description of the type of `value` appropriate for an error message.
+    ///
+    /// - parameter value: The value whose type to describe.
+    /// - returns: A string describing `value`.
+    /// - precondition: `value` is one of the types below.
+    fileprivate static func _typeDescription(of value: Any) -> String {
+        if value is NSNull {
+            return "a null value"
+        } else if value is NSNumber /* FIXME: If swift-corelibs-foundation isn't updated to use NSNumber, this check will be necessary: || value is Int || value is Double */ {
+            return "a number"
+        } else if value is String {
+            return "a string/data"
+        } else if value is [Any] {
+            return "an array"
+        } else if value is [String : Any] {
+            return "a dictionary"
+        } else {
+            // This should never happen -- we somehow have a non-JSON type here.
+            preconditionFailure("Invalid storage type \(type(of: value)).")
+        }
+    }
+}