[WIP] CoreTransferable attachments

Author: grynspan

Package.swift

@@ -162,6 +162,7 @@ let package = Package(
         "_Testing_AppKit",
         "_Testing_CoreGraphics",
         "_Testing_CoreImage",
+        "_Testing_CoreTransferable",
         "_Testing_Foundation",
         "_Testing_UIKit",
         "_Testing_WinSDK",
@@ -264,6 +265,15 @@ let package = Package(
       exclude: ["CMakeLists.txt"],
       swiftSettings: .packageSettings + .enableLibraryEvolution() + .moduleABIName("_Testing_CoreImage")
     ),
+    .target(
+      name: "_Testing_CoreTransferable",
+      dependencies: [
+        "Testing",
+      ],
+      path: "Sources/Overlays/_Testing_CoreTransferable",
+      exclude: ["CMakeLists.txt"],
+      swiftSettings: .packageSettings + .enableLibraryEvolution() + .moduleABIName("_Testing_CoreTransferable")
+    ),
     .target(
       name: "_Testing_Foundation",
       dependencies: [

Sources/Overlays/CMakeLists.txt

@@ -9,6 +9,7 @@
 add_subdirectory(_Testing_AppKit)
 add_subdirectory(_Testing_CoreGraphics)
 add_subdirectory(_Testing_CoreImage)
+add_subdirectory(_Testing_CoreTransferable)
 add_subdirectory(_Testing_Foundation)
 add_subdirectory(_Testing_UIKit)
 add_subdirectory(_Testing_WinSDK)

Sources/Overlays/_Testing_CoreTransferable/Attachments/Attachment+Transferable.swift

@@ -0,0 +1,48 @@
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2026 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(CoreTransferable)
+public import Testing
+public import CoreTransferable
+
+public import UniformTypeIdentifiers
+
+@_spi(Experimental)
+@available(macOS 15.2, *)
+extension Attachment {
+  /// Initialize an instance of this type that encloses the given transferable
+  /// value.
+  ///
+  /// - Parameters:
+  ///   - transferableValue: The value that will be attached to the output of
+  ///     the test run.
+  ///   - preferredName: The preferred name of the attachment to use when saving
+  ///     it. If `nil`, the testing library attempts to generate a reasonable
+  ///     filename for the attached value.
+  ///   - sourceLocation: The source location of the call to this initializer.
+  ///     This value is used when recording issues associated with the
+  ///     attachment.
+  ///
+  /// - Throws: Any error that occurs while exporting `transferableValue`.
+  ///
+  /// Use this initializer to create an instance of ``Attachment`` from a value
+  /// that conforms to the [`Transferable`](https://developer.apple.com/documentation/coretransferable/transferable)
+  /// protocol.
+  public init<T>(
+    transferring transferableValue: T,
+    as contentType: UTType? = nil,
+    named preferredName: String? = nil,
+    sourceLocation: SourceLocation = #_sourceLocation
+  ) async throws where T: Transferable, AttachableValue == _AttachableTransferableWrapper<T> {
+    let transferableWrapper = try await _AttachableTransferableWrapper(transferring: transferableValue, as: contentType)
+    self.init(transferableWrapper, named: preferredName, sourceLocation: sourceLocation)
+  }
+}
+#endif

Sources/Overlays/_Testing_CoreTransferable/Attachments/_AttachableTransferableWrapper.swift

@@ -0,0 +1,67 @@
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2026 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(CoreTransferable)
+public import Testing
+public import CoreTransferable
+
+private import Foundation
+import UniformTypeIdentifiers
+
+private enum TransferableAttachmentError: Error {
+  case suitableContentTypeNotFound
+}
+
+/// A wrapper type representing transferable values that can be attached
+/// indirectly.
+///
+/// You do not need to use this type directly. Instead, initialize an instance
+/// of ``Attachment`` using an instance of a type conforming to the [`Transferable`](https://developer.apple.com/documentation/coretransferable/transferable)
+/// protocol.
+@_spi(Experimental)
+@available(macOS 15.2, *)
+public struct _AttachableTransferableWrapper<T>: Sendable where T: Transferable {
+  private var _transferableValue: T
+  private var _contentType: UTType
+  private var _bytes: Data
+
+  init(transferring transferableValue: T, as contentType: UTType?) async throws {
+    _transferableValue = transferableValue
+
+    let contentType = contentType ?? transferableValue.exportedContentTypes()
+      .first { $0.conforms(to: .data) }
+    guard let contentType else {
+      throw TransferableAttachmentError.suitableContentTypeNotFound
+    }
+    _contentType = contentType
+
+    _bytes = try await _transferableValue.exported(as: contentType)
+  }
+}
+
+// MARK: -
+
+@_spi(Experimental)
+@available(macOS 15.2, *)
+extension _AttachableTransferableWrapper: AttachableWrapper {
+  public var wrappedValue: T {
+    _transferableValue
+  }
+
+  public func withUnsafeBytes<R>(for attachment: borrowing Attachment<Self>, _ body: (UnsafeRawBufferPointer) throws -> R) throws -> R {
+    try _bytes.withUnsafeBytes(body)
+  }
+
+  public borrowing func preferredName(for attachment: borrowing Attachment<Self>, basedOn suggestedName: String) -> String {
+    let baseName = _transferableValue.suggestedFilename ?? suggestedName
+    return (baseName as NSString).appendingPathExtension(for: _contentType)
+  }
+}
+#endif

Sources/Overlays/_Testing_CoreTransferable/CMakeLists.txt

@@ -0,0 +1,25 @@
+# This source file is part of the Swift.org open source project
+#
+# Copyright (c) 2026 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 (CMAKE_SYSTEM_NAME STREQUAL "Darwin")
+include(ModuleABIName)
+  add_library(_Testing_CoreTransferable
+    Attachments/_AttachableTransferableWrapper.swift
+    Attachments/Attachment+Transferable.swift
+    ReexportTesting.swift)
+
+  target_link_libraries(_Testing_CoreTransferable PUBLIC
+    Testing
+    _Testing_CoreGraphics)
+
+  target_compile_options(_Testing_CoreTransferable PRIVATE
+    -enable-library-evolution
+    -emit-module-interface -emit-module-interface-path $<TARGET_PROPERTY:_Testing_CoreTransferable,Swift_MODULE_DIRECTORY>/_Testing_CoreTransferable.swiftinterface)
+
+  _swift_testing_install_target(_Testing_CoreTransferable)
+endif()

Sources/Overlays/_Testing_CoreTransferable/ReexportTesting.swift

@@ -0,0 +1,11 @@
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2026 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
+//
+
+@_exported @_spi(Experimental) @_spi(ForToolsIntegrationOnly) public import Testing

Sources/Testing/Testing.swiftcrossimport/CoreTransferable.swiftoverlay

@@ -0,0 +1,3 @@
+version: 1
+modules:
+- name: _Testing_CoreTransferable