title: Xcode 11 crashes when copy/pasting views from different storyboards
body: <p>I have a problem with Xcode 11 running on Catalina (it had the same problem with Moave).
  When I try to copy/paste a view or a ViewController from one storyboard to another Xcode crashes with this exception:</p>
  
  <pre><code>...
  Exception Type:        EXC_CRASH (SIGABRT)
  Exception Codes:       0x0000000000000000, 0x0000000000000000
  Exception Note:        EXC_CORPSE_NOTIFY
  
  Application Specific Information:
  Sending paste: to IBStructureAreaDockView from &lt;NSMenuItem: 0x7fe24030ddd0 Paste&gt;
  ProductBuildVersion: 11A1027
  ASSERTION FAILURE in /Library/Caches/com.apple.xbs/Sources/IDEInterfaceBuilder/IDEInterfaceBuilder-15400/InterfaceBuilderKit/WidgetIntegration/View/IBViewIntegration.m:2451
  Details:  There should only be 1 parent of all the constraint items extracted from the pasteboard: {(
  )}
  Object:   &lt;IBUIView: 0x7fe23db1c600&gt;
  Method:   -ibDidExtractObjects:fromPasteboard:intoDocument:context:
  Thread:   &lt;NSThread: 0x7fe23ac17e80&gt;{number = 1, name = main}
  Hints:   
    0: Sending paste: to IBStructureAreaDockView from &lt;NSMenuItem: 0x7fe24030ddd0 Paste&gt;
  Backtrace:
    0   -[IDEAssertionHandler handleFailureInMethod:object:fileName:lineNumber:assertionSignature:messageFormat:arguments:] (in IDEKit)
    1   _DVTAssertionHandler (in DVTFoundation)
    2   _DVTAssertionFailureHandler (in DVTFoundation)
    3   -[NSView(IBViewIntegration) ibDidExtractObjects:fromPasteboard:intoDocument:context:] (in IDEInterfaceBuilderKit)
    4   -[IBUIView(IBUIViewIntegration) ibDidExtractObjects:fromPasteboard:intoDocument:context:] (in IDEInterfaceBuilderCocoaTouchIntegration)
    5   -[IBDocument ibDidExtractObjects:fromPasteboard:context:] (in IDEInterfaceBuilderKit)
    6   -[IBDocument insertObjectsFromPasteboard:ofType:asChildrenOfObject:atIndex:context:finishExtractingObjectsBlock:] (in IDEInterfaceBuilderKit)
    7   -[IBDocument insertOrMoveChildrenFromPasteboard:ofType:asChildrenOfObject:atIndex:context:finishExtractingObjectsBlock:] (in IDEInterfaceBuilderKit)
    8   -[IBDocument addOrMoveChildrenFromPasteboard:ofType:toObject:context:finishExtractingObjectsBlock:] (in IDEInterfaceBuilderKit)
    9   -[IBStoryboardDocument addOrMoveChildrenFromPasteboard:ofType:toSceneGroup:context:] (in IDEInterfaceBuilderKit)
   10   -[IBSceneDockViewController performDockPasteWithPasteboard:context:] (in IDEInterfaceBuilderKit)
   11   -[IBSceneDockViewController dockViewPerformPaste:] (in IDEInterfaceBuilderKit)
   12   -[IBStructureAreaDockView paste:] (in IDEInterfaceBuilderKit)
   13   -[NSApplication(NSResponder) sendAction:to:from:] (in AppKit)
   14   __37-[DVTApplication sendAction:to:from:]_block_invoke.86 (in DVTKit)
   15   DVTInvokeWithFailureHint (in DVTFoundation)
   16   -[DVTApplication sendAction:to:from:] (in DVTKit)
   17   -[NSMenuItem _corePerformAction] (in AppKit)
   18   -[NSCarbonMenuImpl performActionWithHighlightingForItemAtIndex:] (in AppKit)
   19   -[NSMenu performKeyEquivalent:] (in AppKit)
   20   routeKeyEquivalent (in AppKit)
   21   -[NSApplication(NSEvent) sendEvent:] (in AppKit)
   22   -[IDEApplication sendEvent:] (in IDEKit)
   23   -[NSApplication run] (in AppKit)
   24   NSApplicationMain (in AppKit)
   25   main (in Xcode)
   26   start (in libdyld.dylib)
  
  Performing @selector(paste:) from sender NSMenuItem 0x7fe24030ddd0
  abort() called
  
  Application Specific Signatures:
  [parentsOfItemsInConstraints count] == 1
  ...
  </code></pre>
  
  <p>Is it happening to someone else? Is this something not supported by storyboard?</p>