Unreal Engine Issues and Bug Tracker (UE-50300)

Description

The editor crashes when trying to undo a default class change for a child widget after that widget has been compiled.

This did not happen in 4.16, it appears to be a regression.

Steps to Reproduce

Open the editor
Create a new widget blueprint
Name the widget blueprint "parent"
Create a new widget blueprint
Name the widget blueprint "UndoCrash"
Open "Parent"
Add "UndoCrash" to Parent's designer tab
Compile and save
Open "UndoCrash"
Open the event graph
Check "Is Focusable" so that it's true
Click compile (compile and then undo this order is important)
Use Ctrl+Z to undo

Result: The editor crashes when trying to undo the change
Expected: The change that was made would be undone

Callstack

Fatal error: [File:D:\Build\++UE4+Release-4.17+Compile\Sync\Engine\Source\Runtime\CoreUObject\Private\UObject\UObjectGlobals.cpp] [Line: 2289] Objects have the same fully qualified name but different paths. New Object: REINST_UndoCrash_C_13 /Engine/Transient.World_4:Parent_C_5.WidgetTree_30.UndoCrash Existing Object: UndoCrash_C /Engine/Transient.World_4:Parent_C_5.WidgetTree_30.UndoCrash

UE4Editor_Core!FDebug::AssertFailed() [d:\build\++ue4+release-4.17+compile\sync\engine\source\runtime\core\private\misc\assertionmacros.cpp:349]
UE4Editor_CoreUObject!StaticAllocateObject() [d:\build\++ue4+release-4.17+compile\sync\engine\source\runtime\coreuobject\private\uobject\uobjectglobals.cpp:2284]
UE4Editor_CoreUObject!StaticConstructObject_Internal() [d:\build\++ue4+release-4.17+compile\sync\engine\source\runtime\coreuobject\private\uobject\uobjectglobals.cpp:3121]
UE4Editor_CoreUObject!FDuplicateDataWriter::GetDuplicatedObject() [d:\build\++ue4+release-4.17+compile\sync\engine\source\runtime\coreuobject\private\serialization\duplicatedatawriter.cpp:145]
UE4Editor_CoreUObject!FDuplicateDataWriter::operator<<() [d:\build\++ue4+release-4.17+compile\sync\engine\source\runtime\coreuobject\private\serialization\duplicatedatawriter.cpp:67]
UE4Editor_CoreUObject!UObjectProperty::SerializeItem() [d:\build\++ue4+release-4.17+compile\sync\engine\source\runtime\coreuobject\private\uobject\propertyobject.cpp:64]
UE4Editor_CoreUObject!FPropertyTag::SerializeTaggedProperty() [d:\build\++ue4+release-4.17+compile\sync\engine\source\runtime\coreuobject\private\uobject\propertytag.cpp:188]
UE4Editor_CoreUObject!UStruct::SerializeTaggedProperties() [d:\build\++ue4+release-4.17+compile\sync\engine\source\runtime\coreuobject\private\uobject\class.cpp:1154]
UE4Editor_CoreUObject!UObject::SerializeScriptProperties() [d:\build\++ue4+release-4.17+compile\sync\engine\source\runtime\coreuobject\private\uobject\obj.cpp:1282]
UE4Editor_CoreUObject!UObject::Serialize() [d:\build\++ue4+release-4.17+compile\sync\engine\source\runtime\coreuobject\private\uobject\obj.cpp:1216]
UE4Editor_CoreUObject!StaticDuplicateObjectEx() [d:\build\++ue4+release-4.17+compile\sync\engine\source\runtime\coreuobject\private\uobject\uobjectglobals.cpp:2019]
UE4Editor_UMG!UUserWidget::DuplicateAndInitializeFromWidgetTree() [d:\build\++ue4+release-4.17+compile\sync\engine\source\runtime\umg\private\userwidget.cpp:402]
UE4Editor_UMGEditor!FWidgetBlueprintEditor::UpdatePreview() [d:\build\++ue4+release-4.17+compile\sync\engine\source\editor\umgeditor\private\widgetblueprinteditor.cpp:868]
UE4Editor_UMGEditor!FWidgetBlueprintEditor::RefreshPreview() [d:\build\++ue4+release-4.17+compile\sync\engine\source\editor\umgeditor\private\widgetblueprinteditor.cpp:751]
UE4Editor_UMGEditor!FWidgetBlueprintEditor::OnBlueprintChangedImpl() [d:\build\++ue4+release-4.17+compile\sync\engine\source\editor\umgeditor\private\widgetblueprinteditor.cpp:309]
UE4Editor_Kismet!TBaseSPMethodDelegateInstance<0,FBlueprintEditor,0,TTypeWrapper<void> __cdecl(UBlueprint * __ptr64)>::Execute() [d:\build\++ue4+release-4.17+compile\sync\engine\source\runtime\core\public\delegates\delegateinstancesimpl.h:327]
UE4Editor_Kismet!TBaseSPMethodDelegateInstance<0,FBlueprintEditor,0,void __cdecl(UBlueprint * __ptr64)>::ExecuteIfSafe() [d:\build\++ue4+release-4.17+compile\sync\engine\source\runtime\core\public\delegates\delegateinstancesimpl.h:434]
UE4Editor_Engine!TBaseMulticastDelegate<void,UBlueprint * __ptr64>::Broadcast() [d:\build\++ue4+release-4.17+compile\sync\engine\source\runtime\core\public\delegates\delegatesignatureimpl.inl:937]
UE4Editor_UnrealEd!FBlueprintEditorUtils::MarkBlueprintAsStructurallyModified() [d:\build\++ue4+release-4.17+compile\sync\engine\source\editor\unrealed\private\kismet2\blueprinteditorutils.cpp:2109]
UE4Editor_Kismet!FixSubObjectReferencesPostUndoRedo() [d:\build\++ue4+release-4.17+compile\sync\engine\source\editor\kismet\private\blueprinteditormodule.cpp:164]
UE4Editor_UnrealEd!UEditorEngine::BroadcastPostUndo() [d:\build\++ue4+release-4.17+compile\sync\engine\source\editor\unrealed\private\editorserver.cpp:5074]
UE4Editor_UnrealEd!UEditorEngine::HandleTransactorUndo() [d:\build\++ue4+release-4.17+compile\sync\engine\source\editor\unrealed\private\editorserver.cpp:1185]
UE4Editor_UnrealEd!TBaseUObjectMethodDelegateInstance<0,UEditorEngine,TTypeWrapper<void> __cdecl(FUndoSessionContext,bool)>::Execute() [d:\build\++ue4+release-4.17+compile\sync\engine\source\runtime\core\public\delegates\delegateinstancesimpl.h:766]
UE4Editor_UnrealEd!TBaseUObjectMethodDelegateInstance<0,UEditorEngine,void __cdecl(FUndoSessionContext,bool)>::ExecuteIfSafe() [d:\build\++ue4+release-4.17+compile\sync\engine\source\runtime\core\public\delegates\delegateinstancesimpl.h:856]
UE4Editor_UnrealEd!TBaseMulticastDelegate<void,FUndoSessionContext,bool>::Broadcast() [d:\build\++ue4+release-4.17+compile\sync\engine\source\runtime\core\public\delegates\delegatesignatureimpl.inl:937]
UE4Editor_UnrealEd!UTransBuffer::Undo() [d:\build\++ue4+release-4.17+compile\sync\engine\source\editor\unrealed\private\editortransaction.cpp:876]
UE4Editor_Kismet!TBaseSPMethodDelegateInstance<0,FBlueprintEditor,0,TTypeWrapper<void> __cdecl(void)>::Execute() [d:\build\++ue4+release-4.17+compile\sync\engine\source\runtime\core\public\delegates\delegateinstancesimpl.h:327]
UE4Editor_Kismet!TBaseSPMethodDelegateInstance<0,FBlueprintEditor,0,void __cdecl(void)>::ExecuteIfSafe() [d:\build\++ue4+release-4.17+compile\sync\engine\source\runtime\core\public\delegates\delegateinstancesimpl.h:434]
UE4Editor_Slate!FUICommandList::ConditionalProcessCommandBindings() [d:\build\++ue4+release-4.17+compile\sync\engine\source\runtime\slate\private\framework\commands\uicommandlist.cpp:216]
UE4Editor_Slate!FUICommandList::ProcessCommandBindings() [d:\build\++ue4+release-4.17+compile\sync\engine\source\runtime\slate\private\framework\commands\uicommandlist.cpp:160]
UE4Editor_UnrealEd!FBaseToolkit::ProcessCommandBindings() [d:\build\++ue4+release-4.17+compile\sync\engine\source\editor\unrealed\private\toolkits\basetoolkit.cpp:74]
UE4Editor_UnrealEd!SStandaloneAssetEditorToolkitHost::OnKeyDown() [d:\build\++ue4+release-4.17+compile\sync\engine\source\editor\unrealed\private\toolkits\sstandaloneasseteditortoolkithost.cpp:324]
UE4Editor_Slate!<lambda_2afcd964c763e269e2d1a63f3a72f846>::operator()() [d:\build\++ue4+release-4.17+compile\sync\engine\source\runtime\slate\private\framework\application\slateapplication.cpp:4771]
UE4Editor_Slate!FEventRouter::Route<FReply,FEventRouter::FBubblePolicy,FKeyEvent,<lambda_2afcd964c763e269e2d1a63f3a72f846> >() [d:\build\++ue4+release-4.17+compile\sync\engine\source\runtime\slate\private\framework\application\slateapplication.cpp:232]
UE4Editor_Slate!FEventRouter::RouteAlongFocusPath<FEventRouter::FBubblePolicy,<lambda_2afcd964c763e269e2d1a63f3a72f846>,FKeyEvent>() [d:\build\++ue4+release-4.17+compile\sync\engine\source\runtime\slate\private\framework\application\slateapplication.cpp:214]
UE4Editor_Slate!FSlateApplication::ProcessKeyDownEvent() [d:\build\++ue4+release-4.17+compile\sync\engine\source\runtime\slate\private\framework\application\slateapplication.cpp:4769]
UE4Editor_Slate!FSlateApplication::OnKeyDown() [d:\build\++ue4+release-4.17+compile\sync\engine\source\runtime\slate\private\framework\application\slateapplication.cpp:4681]
UE4Editor_Core!FWindowsApplication::ProcessDeferredMessage() [d:\build\++ue4+release-4.17+compile\sync\engine\source\runtime\core\private\windows\windowsapplication.cpp:1553]
UE4Editor_Core!FWindowsApplication::DeferMessage() [d:\build\++ue4+release-4.17+compile\sync\engine\source\runtime\core\private\windows\windowsapplication.cpp:2161]
UE4Editor_Core!FWindowsApplication::ProcessMessage() [d:\build\++ue4+release-4.17+compile\sync\engine\source\runtime\core\private\windows\windowsapplication.cpp:881]
UE4Editor_Core!FWindowsApplication::AppWndProc() [d:\build\++ue4+release-4.17+compile\sync\engine\source\runtime\core\private\windows\windowsapplication.cpp:721]
user32
user32
UE4Editor_Core!FWindowsPlatformMisc::PumpMessages() [d:\build\++ue4+release-4.17+compile\sync\engine\source\runtime\core\private\windows\windowsplatformmisc.cpp:1009]
UE4Editor!FEngineLoop::Tick() [d:\build\++ue4+release-4.17+compile\sync\engine\source\runtime\launch\private\launchengineloop.cpp:3151]
UE4Editor!GuardedMain() [d:\build\++ue4+release-4.17+compile\sync\engine\source\runtime\launch\private\launch.cpp:166]
UE4Editor!GuardedMainWrapper() [d:\build\++ue4+release-4.17+compile\sync\engine\source\runtime\launch\private\windows\launchwindows.cpp:134]
UE4Editor!WinMain() [d:\build\++ue4+release-4.17+compile\sync\engine\source\runtime\launch\private\windows\launchwindows.cpp:210]
UE4Editor!__scrt_common_main_seh() [f:\dd\vctools\crt\vcstartup\src\startup\exe_common.inl:253]
kernel32
ntdll

Community References

UE4.17 crashes when use widget undo

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Cannot Reproduce

Component	UE - Editor - UI Systems
Affects Versions	4.17.1, 4.18, 4.21
Target Fix	4.23

Created	Sep 25, 2017
Resolved	Aug 12, 2019
Updated	Apr 16, 2021

UE-50300

Crash when Undoing the change to a default class setting for widgets

Crash when Undoing the change to a default class setting for widgets

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