Open Radar

 
Summary:
Implementing drag-drop from an NSCollectionView with a NSFilesPromisePboardType causes some unexpected behaviour when used on macOS Sierra and El Capitan. The implementation that works for macOS Sierra, crashes on El Capitan.

I've used the SlidesMagic NSCollectionView project from Ray Wenderlich as a base for the attached example project.

The project contains various setups that can be used for testing in ViewController.swift, starting here from line 131. I've attached the project, but it can also be found here:

https://github.com/boyvanamstel/NSFilesPromisePboardType-NSCollectionView-crash

Steps to Reproduce:
1. Setup the NSCollectionView to allow content to be dragged from the grid.

override func viewDidLoad() {
  super.viewDidLoad()
  collectionView.setDraggingSourceOperationMask(NSDragOperation.copy, forLocal: false)
}

extension ViewController : NSCollectionViewDelegate {

  [...]

  func collectionView(_ collectionView: NSCollectionView, writeItemsAt indexPaths: Set<IndexPath>, to pasteboard: NSPasteboard) -> Bool {
    pasteboard.clearContents()
    pasteboard.declareTypes([NSFilesPromisePboardType], owner: self)
    pasteboard.setPropertyList(["jpg"], forType: NSFilesPromisePboardType)
    return true
  }

  func collectionView(_ collectionView: NSCollectionView, namesOfPromisedFilesDroppedAtDestination dropURL: URL, forDraggedItemsAt indexPaths: Set<IndexPath>) -> [String] {

    // Write to file

    return [dropURL.appendingPathComponent("test.jpg").absoluteString]
  }

  // Seems redundant, but it's required by El Capitan. It causes a crash when running on El Capitan.
  func collectionView(_ collectionView: NSCollectionView, namesOfPromisedFilesDroppedAtDestination dropURL: URL, forDraggedItemsAt indexes: IndexSet) -> [String] {

    // Write to file

    return [dropURL.appendingPathComponent("test.jpg").absoluteString]
  }

}

2. Compile the project and deploy it to a Mac running macOS El Capitan and one running macOS Sierra.

3. Try dragging one of the images from the NSCollectionView onto your Desktop, or a Finder window.

4. Drop the item.

Expected Results:
1. The application should indicate that the item is draggable and show its intent to drop.

2. After dropping, nothing much should happen, but the app should keep running.

Actual Results:
On Sierra:

The app keeps running.

On El Capitan:

The app crashes, taking Finder with it, with the following crash report:

Process:               SlidesMagic [913]
Path:                  /Users/USER/Desktop/SlidesMagic.app/Contents/MacOS/SlidesMagic
Identifier:            com.razeware.SlidesMagic
Version:               1.0 (1)
Code Type:             X86-64 (Native)
Parent Process:        ??? [1]
Responsible:           SlidesMagic [913]
User ID:               501

Date/Time:             2016-09-28 11:35:18.315 +0200
OS Version:            Mac OS X 10.11.6 (15G31)
Report Version:        11
Anonymous UUID:        E2E828C4-F4C1-2EE0-6239-2E04C93C5A34

Sleep/Wake UUID:       FF367448-5269-4753-9E1F-5EA813163500

Time Awake Since Boot: 7300 seconds

System Integrity Protection: enabled

Crashed Thread:        0  Dispatch queue: com.apple.main-thread

Exception Type:        EXC_BAD_INSTRUCTION (SIGILL)
Exception Codes:       0x0000000000000001, 0x0000000000000000
Exception Note:        EXC_CORPSE_NOTIFY

[...]

Thread 0 Crashed:: Dispatch queue: com.apple.main-thread
0   libswiftFoundation.dylib        0x000000010bf5b353 _TZFV10Foundation8IndexSet36_unconditionallyBridgeFromObjectiveCfGSqCSo10NSIndexSet_S0_ + 307
1   SlidesMagic                     0x000000010b910b15 _TToFC11SlidesMagic14ViewController14collectionViewfTCSo16NSCollectionView40namesOfPromisedFilesDroppedAtDestinationV10Foundation3URL17forDraggedItemsAtVS2_8IndexSet_GSaSS_ + 101
2   com.apple.AppKit                0x00007fff8b5e0f75 -[NSCollectionView namesOfPromisedFilesDroppedAtDestination:] + 100
3   com.apple.AppKit                0x00007fff8b56024d -[NSFilePromiseDragSource getFilenamesAndDropLocation] + 70
4   com.apple.AppKit                0x00007fff8b0b9923 -[NSFilePromiseDragSource pasteboard:provideDataForType:itemIdentifier:] + 79
5   com.apple.AppKit                0x00007fff8b0b83e7 __NSPasteboardProvideData + 331
6   com.apple.CoreFoundation        0x00007fff94f3cc04 __CFPasteboardClientCallBack + 1364
7   com.apple.CoreFoundation        0x00007fff94f18628 __CFMessagePortPerform + 584
8   com.apple.CoreFoundation        0x00007fff94e80019 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 41
9   com.apple.CoreFoundation        0x00007fff94e7ff89 __CFRunLoopDoSource1 + 473
10  com.apple.CoreFoundation        0x00007fff94e779bb __CFRunLoopRun + 2171
11  com.apple.CoreFoundation        0x00007fff94e76ed8 CFRunLoopRunSpecific + 296
12  com.apple.CoreFoundation        0x00007fff94edc925 CFMessagePortSendRequest + 949
13  com.apple.HIServices            0x00007fff9330e7dc SendDragIPCMessage + 530
14  com.apple.HIServices            0x00007fff93306b29 SendDropMessage + 64
15  com.apple.HIServices            0x00007fff93305807 DragInApplication + 505
16  com.apple.HIServices            0x00007fff933046cf CoreDragStartDragging + 705
17  com.apple.AppKit                0x00007fff8b01f369 -[NSCoreDragManager _dragUntilMouseUp:accepted:] + 1010
18  com.apple.AppKit                0x00007fff8b01c557 -[NSCoreDragManager dragImage:fromWindow:at:offset:event:pasteboard:source:slideBack:] + 1212
19  com.apple.AppKit                0x00007fff8b01c089 -[NSWindow(NSDrag) dragImage:at:offset:event:pasteboard:source:slideBack:] + 135
20  com.apple.AppKit                0x00007fff8b5e1543 -[NSCollectionView _startDragWithItemsAtIndexPaths:event:pasteboard:] + 345
21  com.apple.AppKit                0x00007fff8b5e178a -[NSCollectionView _writeToPasteboardAndBeginDragForIndexPaths:event:] + 182
22  com.apple.AppKit                0x00007fff8b45559f -[NSCollectionViewMouseSession _performDragFromMouseDown:] + 774
23  com.apple.AppKit                0x00007fff8b455c5e -[NSCollectionViewMouseSession handleEvent:] + 927
24  com.apple.AppKit                0x00007fff8b45644d -[NSCollectionViewMouseSession trackWithEvent:] + 132
25  com.apple.AppKit                0x00007fff8b5e0724 -[NSCollectionView mouseDown:] + 213
26  com.apple.AppKit                0x00007fff8aeed634 forwardMethod + 126
27  com.apple.AppKit                0x00007fff8aeed634 forwardMethod + 126
28  com.apple.AppKit                0x00007fff8aeed634 forwardMethod + 126
29  com.apple.AppKit                0x00007fff8afdbc8e -[NSControl mouseDown:] + 1091
30  com.apple.AppKit                0x00007fff8b5303c9 -[NSWindow _handleMouseDownEvent:isDelayedEvent:] + 6322
31  com.apple.AppKit                0x00007fff8b5313ad -[NSWindow _reallySendEvent:isDelayedEvent:] + 212
32  com.apple.AppKit                0x00007fff8af70539 -[NSWindow sendEvent:] + 517
33  com.apple.AppKit                0x00007fff8aef0a38 -[NSApplication sendEvent:] + 2540
34  com.apple.AppKit                0x00007fff8ad57df2 -[NSApplication run] + 796
35  com.apple.AppKit                0x00007fff8ad21368 NSApplicationMain + 1176
36  SlidesMagic                     0x000000010b916cb4 main + 84
37  libdyld.dylib                   0x00007fff975f25ad start + 1

Version:
Xcode Version 8.0 (8A218a) & 8.1 beta (8T29o)

Notes:
I have not been able to test compiling the app on macOS El Capitan. The bug seems to be present in the latest beta versions of Xcode and its SDKs.

Configuration:
OS X 10.12 Sierra (16A323)
Xcode Version 8.0 (8A218a) & 8.1 beta (8T29o)
2,3 GHz Intel Core i7
16 GB 1600 MHz DDR3

Attachments:
'SlidesMagic-bugreport.zip' and 'SlidesMagic_2016-09-28-113531_Dangers-Mac.crash' were successfully uploaded.