Add default Attachable implementation for types that conform to BOTH coding protocols

Author: grynspan

Sources/Overlays/_Testing_Foundation/Attachments/ContiguousBytes+Test.Attachable.swift renamed to Sources/Overlays/_Testing_Foundation/Attachments/Test.Attachable+ContiguousBytes.swift

@@ -13,7 +13,7 @@
 public import Foundation
 
 @_spi(Experimental)
-extension ContiguousBytes where Self: Test.Attachable {
+extension Test.Attachable where Self: ContiguousBytes {
   public func withUnsafeBufferPointer<R>(for attachment: borrowing Test.Attachment, _ body: (UnsafeRawBufferPointer) throws -> R) throws -> R {
     try withUnsafeBytes(body)
   }

Sources/Overlays/_Testing_Foundation/Attachments/Test.Attachable+Encodable&NSSecureCoding.swift

@@ -0,0 +1,25 @@
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2024 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 Swift project authors
+//
+
+#if canImport(Foundation)
+@_spi(Experimental) public import Testing
+public import Foundation
+
+@_spi(Experimental)
+extension Test.Attachable where Self: Encodable & NSSecureCoding {
+  @_documentation(visibility: private)
+  public func withUnsafeBufferPointer<R>(for attachment: borrowing Test.Attachment, _ body: (UnsafeRawBufferPointer) throws -> R) throws -> R {
+    func open(_ value: borrowing some Encodable & Test.Attachable) throws -> R {
+      return try value.withUnsafeBufferPointer(for: attachment, body)
+    }
+    return try open(self)
+  }
+}
+#endif

Sources/Overlays/_Testing_Foundation/Attachments/Encodable+Test.Attachable.swift renamed to Sources/Overlays/_Testing_Foundation/Attachments/Test.Attachable+Encodable.swift

@@ -16,7 +16,7 @@ private import Foundation
 // encoding to JSON. This lets developers provide trivial conformance to the
 // protocol for types that already support Codable.
 @_spi(Experimental)
-extension Encodable where Self: Test.Attachable {
+extension Test.Attachable where Self: Encodable {
   /// Encode this value into a buffer using either [`PropertyListEncoder`](https://developer.apple.com/documentation/foundation/propertylistencoder)
   /// or [`JSONEncoder`](https://developer.apple.com/documentation/foundation/jsonencoder),
   /// then call a function and pass that buffer to it.
@@ -43,7 +43,11 @@ extension Encodable where Self: Test.Attachable {
   /// | `".plist"` | Binary property list | [`PropertyListEncoder`](https://developer.apple.com/documentation/foundation/propertylistencoder) |
   /// | None, `".json"` | JSON | [`JSONEncoder`](https://developer.apple.com/documentation/foundation/jsonencoder) |
   ///
-  /// OpenStep-style property lists are not supported.
+  /// OpenStep-style property lists are not supported. If a value conforms to
+  /// _both_ [`Encodable`](https://developer.apple.com/documentation/swift/encodable)
+  /// _and_ [`NSSecureCoding`](https://developer.apple.com/documentation/foundation/nssecurecoding),
+  /// the default implementation of this function uses the value's conformance
+  /// to `Encodable`.
   ///
   /// - Note: On Apple platforms, if the attachment's preferred name includes
   ///   some other path extension, that path extension must represent a type

Sources/Overlays/_Testing_Foundation/Attachments/NSSecureCoding+Test.Attachable.swift renamed to Sources/Overlays/_Testing_Foundation/Attachments/Test.Attachable+NSSecureCoding.swift

@@ -16,7 +16,7 @@ public import Foundation
 // NSSecureCoding-conformant classes by default. The implementation uses
 // NSKeyedArchiver for encoding.
 @_spi(Experimental)
-extension NSSecureCoding where Self: Test.Attachable {
+extension Test.Attachable where Self: NSSecureCoding {
   /// Encode this object using [`NSKeyedArchiver`](https://developer.apple.com/documentation/foundation/nskeyedarchiver)
   /// into a buffer, then call a function and pass that buffer to it.
   ///
@@ -41,7 +41,11 @@ extension NSSecureCoding where Self: Test.Attachable {
   /// | `".xml"` | XML property list | [`NSKeyedArchiver`](https://developer.apple.com/documentation/foundation/nskeyedarchiver) |
   /// | None, `".plist"` | Binary property list | [`NSKeyedArchiver`](https://developer.apple.com/documentation/foundation/nskeyedarchiver) |
   ///
-  /// OpenStep-style property lists are not supported.
+  /// OpenStep-style property lists are not supported. If a value conforms to
+  /// _both_ [`Encodable`](https://developer.apple.com/documentation/swift/encodable)
+  /// _and_ [`NSSecureCoding`](https://developer.apple.com/documentation/foundation/nssecurecoding),
+  /// the default implementation of this function uses the value's conformance
+  /// to `Encodable`.
   ///
   /// - Note: On Apple platforms, if the attachment's preferred name includes
   ///   some other path extension, that path extension must represent a type

Tests/TestingTests/AttachmentTests.swift

@@ -541,6 +541,23 @@ final class MySecureCodingAttachable: NSObject, NSSecureCoding, Test.Attachable,
   }
 }
 
+final class MyCodableAndSecureCodingAttachable: NSObject, Codable, NSSecureCoding, Test.Attachable, Sendable {
+  let string: String
+
+  static var supportsSecureCoding: Bool {
+    true
+  }
+
+  func encode(with coder: NSCoder) {
+    coder.encode(string, forKey: "string")
+  }
+
+  required init?(coder: NSCoder) {
+    string = (coder.decodeObject(of: NSString.self, forKey: "string") as? String) ?? ""
+  }
+}
+
+
 struct MyContiguousCollectionAttachable: Collection, ContiguousBytes, Test.Attachable, Sendable {
   private var _utf8: String.UTF8View