Add a cross-import overlay with AppKit to allow attaching NSImages.

Package.swift

@@ -54,6 +54,7 @@ let package = Package(
       name: "TestingTests",
       dependencies: [
         "Testing",
+        "_Testing_AppKit",
         "_Testing_CoreGraphics",
         "_Testing_Foundation",
       ],
@@ -95,6 +96,15 @@ let package = Package(
     ),
 
     // Cross-import overlays (not supported by Swift Package Manager)
+    .target(
+      name: "_Testing_AppKit",
+      dependencies: [
+        "Testing",
+        "_Testing_CoreGraphics",
+      ],
+      path: "Sources/Overlays/_Testing_AppKit",
+      swiftSettings: .packageSettings
+    ),
     .target(
       name: "_Testing_CoreGraphics",
       dependencies: [

Sources/Overlays/_Testing_AppKit/Attachments/NSImage+AttachableAsCGImage.swift

@@ -0,0 +1,95 @@
+//
+// 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 SWT_TARGET_OS_APPLE && canImport(AppKit)
+public import AppKit
+@_spi(ForSwiftTestingOnly) @_spi(Experimental) public import _Testing_CoreGraphics
+
+@_spi(Experimental)
+extension NSImage: AttachableAsCGImage {
+  public var attachableCGImage: CGImage {
+    get throws {
+      let ctm = AffineTransform(scale: _attachmentScaleFactor) as NSAffineTransform
+      guard let result = cgImage(forProposedRect: nil, context: nil, hints: [.ctm: ctm]) else {
+        throw ImageAttachmentError.couldNotCreateCGImage
+      }
+      return result
+    }
+  }
+
+  public var _attachmentScaleFactor: CGFloat {
+    let maxRepWidth = representations.lazy
+      .map { CGFloat($0.pixelsWide) / $0.size.width }
+      .filter { $0 > 0.0 }
+      .max()
+    return maxRepWidth ?? 1.0
+  }
+
+  /// Get the base address of the loaded image containing `class`.
+  ///
+  /// - Parameters:
+  ///   - class: The class to look for.
+  ///
+  /// - Returns: The base address of the image containing `class`, or `nil` if
+  ///   no image was found (for instance, if the class is generic or dynamically
+  ///   generated.)
+  ///
+  /// "Image" in this context refers to a binary/executable image.
+  private static func _baseAddressOfImage(containing `class`: AnyClass) -> UnsafeRawPointer? {
+    let classAsAddress = Unmanaged.passUnretained(`class` as AnyObject).toOpaque()
+
+    var info = Dl_info()
+    guard 0 != dladdr(classAsAddress, &info) else {
+      return nil
+    }
+    return .init(info.dli_fbase)
+  }
+
+  /// The base address of the image containing AppKit's symbols, if known.
+  private static nonisolated(unsafe) let _appKitBaseAddress = _baseAddressOfImage(containing: NSImageRep.self)
+
+  public func _makeCopyForAttachment() -> Self {
+    // If this image is of an NSImage subclass, we cannot reliably make a deep
+    // copy of it because we don't know what its `init(data:)` implementation
+    // might do. Try to make a copy (using NSCopying), but if that doesn't work
+    // then just return `self` verbatim.
+    //
+    // Third-party NSImage subclasses are presumably rare in the wild, so
+    // hopefully this case doesn't pop up too often.
+    guard isMember(of: NSImage.self) else {
+      return self.copy() as? Self ?? self
+    }
+
+    // Check whether the image contains any representations that we don't think
+    // are safe. If it does, then make a "safe" copy.
+    let allImageRepsAreSafe = representations.allSatisfy { imageRep in
+      // NSCustomImageRep includes an arbitrary rendering block that may not be
+      // concurrency-safe in Swift.
+      if imageRep is NSCustomImageRep {
+        return false
+      }
+
+      // Treat all other classes declared in AppKit as safe. We can't reason
+      // about classes declared in other modules, so treat them all as if they
+      // are unsafe.
+      return Self._baseAddressOfImage(containing: type(of: imageRep)) == Self._appKitBaseAddress
+    }
+    if !allImageRepsAreSafe, let safeCopy = tiffRepresentation.flatMap(Self.init(data:)) {
+      // Create a "safe" copy of this image by flattening it to TIFF and then
+      // creating a new NSImage instance from it.
+      return safeCopy
+    }
+
+    // This image appears to be safe to copy directly. (This call should never
+    // fail since we already know `self` is a direct instance of `NSImage`.)
+    return unsafeDowncast(self.copy() as AnyObject, to: Self.self)
+  }
+}
+#endif

Sources/Overlays/_Testing_AppKit/ReexportTesting.swift

@@ -0,0 +1,12 @@
+//
+// 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
+//
+
+@_exported public import Testing
+@_exported public import _Testing_CoreGraphics

Tests/TestingTests/AttachmentTests.swift

@@ -10,14 +10,18 @@
 
 @testable @_spi(Experimental) @_spi(ForToolsIntegrationOnly) import Testing
 private import _TestingInternals
-#if canImport(Foundation)
-import Foundation
-@_spi(Experimental) import _Testing_Foundation
+#if canImport(AppKit)
+import AppKit
+@_spi(Experimental) import _Testing_AppKit
 #endif
 #if canImport(CoreGraphics)
 import CoreGraphics
 @_spi(Experimental) @_spi(ForSwiftTestingOnly) import _Testing_CoreGraphics
 #endif
+#if canImport(Foundation)
+import Foundation
+@_spi(Experimental) import _Testing_Foundation
+#endif
 #if canImport(UniformTypeIdentifiers)
 import UniformTypeIdentifiers
 #endif
@@ -555,6 +559,71 @@ extension AttachmentTests {
       }
     }
 #endif
+
+#if canImport(AppKit)
+    static var nsImage: NSImage {
+      get throws {
+        let cgImage = try cgImage.get()
+        let size = CGSize(width: CGFloat(cgImage.width), height: CGFloat(cgImage.height))
+        return NSImage(cgImage: cgImage, size: size)
+      }
+    }
+
+    @available(_uttypesAPI, *)
+    @Test func attachNSImage() throws {
+      let image = try Self.nsImage
+      let attachment = Attachment(image, named: "diamond.jpg")
+      #expect(attachment.attachableValue.size == image.size) // NSImage makes a copy
+      try attachment.attachableValue.withUnsafeBufferPointer(for: attachment) { buffer in
+        #expect(buffer.count > 32)
+      }
+    }
+
+    @available(_uttypesAPI, *)
+    @Test func attachNSImageWithCustomRep() throws {
+      let image = NSImage(size: NSSize(width: 32.0, height: 32.0), flipped: false) { rect in
+        NSColor.red.setFill()
+        rect.fill()
+        return true
+      }
+      let attachment = Attachment(image, named: "diamond.jpg")
+      #expect(attachment.attachableValue.size == image.size) // NSImage makes a copy
+      try attachment.attachableValue.withUnsafeBufferPointer(for: attachment) { buffer in
+        #expect(buffer.count > 32)
+      }
+    }
+
+    @available(_uttypesAPI, *)
+    @Test func attachNSImageWithSubclassedNSImage() throws {
+      let image = MyImage(size: NSSize(width: 32.0, height: 32.0))
+      image.addRepresentation(NSCustomImageRep(size: image.size, flipped: false) { rect in
+        NSColor.green.setFill()
+        rect.fill()
+        return true
+      })
+
+      let attachment = Attachment(image, named: "diamond.jpg")
+      #expect(attachment.attachableValue === image)
+      #expect(attachment.attachableValue.size == image.size) // NSImage makes a copy
+      try attachment.attachableValue.withUnsafeBufferPointer(for: attachment) { buffer in
+        #expect(buffer.count > 32)
+      }
+    }
+
+    @available(_uttypesAPI, *)
+    @Test func attachNSImageWithSubclassedRep() throws {
+      let image = NSImage(size: NSSize(width: 32.0, height: 32.0))
+      image.addRepresentation(MyImageRep<Int>())
+
+      let attachment = Attachment(image, named: "diamond.jpg")
+      #expect(attachment.attachableValue.size == image.size) // NSImage makes a copy
+      let firstRep = try #require(attachment.attachableValue.representations.first)
+      #expect(!(firstRep is MyImageRep<Int>))
+      try attachment.attachableValue.withUnsafeBufferPointer(for: attachment) { buffer in
+        #expect(buffer.count > 32)
+      }
+    }
+#endif
 #endif
   }
 }
@@ -644,3 +713,42 @@ final class MyCodableAndSecureCodingAttachable: NSObject, Codable, NSSecureCodin
   }
 }
 #endif
+
+#if canImport(AppKit)
+private final class MyImage: NSImage {
+  override init(size: NSSize) {
+    super.init(size: size)
+  }
+
+  required init(pasteboardPropertyList propertyList: Any, ofType type: NSPasteboard.PasteboardType) {
+    fatalError("Unimplemented")
+  }
+
+  required init(coder: NSCoder) {
+    fatalError("Unimplemented")
+  }
+
+  override func copy(with zone: NSZone?) -> Any {
+    // Intentionally make a copy as NSImage instead of MyImage to exercise the
+    // cast-failed code path in the overlay.
+    NSImage()
+  }
+}
+
+private final class MyImageRep<T>: NSImageRep {
+  override init() {
+    super.init()
+    size = NSSize(width: 32.0, height: 32.0)
+  }
+
+  required init?(coder: NSCoder) {
+    fatalError("Unimplemented")
+  }
+
+  override func draw() -> Bool {
+    NSColor.blue.setFill()
+    NSRect(origin: .zero, size: size).fill()
+    return true
+  }
+}
+#endif