Unreal Engine Issues and Bug Tracker (UE-56316)

Description

No user comments in crash group

 2143       		// We should always be the one creating an instance in this case.
 2144       		check(bCreateInstance);
 2145       
 2146       		// Dummy object that's instanced for any editor-only subobject dependencies.
 2147 ***** 		const FString ActualClass = Context.FindGloballyMappedObject(ObjectClass, UClass::StaticClass());
 2148       		const FString NativeType = FEmitHelper::GetCppName(Context.GetFirstNativeOrConvertedClass(ObjectClass));
 2149       		if(!ObjectClass->IsNative())
 2150       		{
 2151       			// make sure CDO has been created for NativeType:
 2152       			Context.AddLine(FString::Printf(TEXT("%s::StaticClass()->GetDefaultObject();"), *NativeType));
 2153       		}
 2154       		Context.AddLine(FString::Printf(
 2155       			TEXT("auto %s = NewObject<%s>(%s, %s, TEXT(\"%s\"));")
 2156       			, *LocalNativeName
 2157       			, *NativeType
 2158       			, *OuterStr
 2159       			, *ActualClass
 2160       			, *Object->GetName().ReplaceCharWithEscapedChar()));
 2161       	}

Steps to Reproduce

Launch the editor with a new, blank C++ project.
Create a new C++ class based on ActorComponent (MyActorComponent).
Wait for compilation/reload to finish, then add to the 'public' section of the UMyActorComponent class in MyActorComponent.h as follows:
```
UPROPERTY()
class USceneComponent* NestedEditorOnlyScene;
```

Also add to the end of UMyActorComponent() constructor in MyActorComponent.cpp as follows:

NestedEditorOnlyScene = CreateEditorOnlyDefaultSubobject<USceneComponent>(TEXT("MyNestedEditorOnlyScene"));

Compile code changes in Visual C++, then either wait for hot reload to finish or close/relaunch the editor to pick them up.
After relaunching the editor with code changes, create a new Actor-based Blueprint class (MyBlueprint).
Double-click the new Blueprint class to edit it, then add a new 'My Actor' component. Compile, save and close the Blueprint editor.
Drag an instance of the new Blueprint class into the current scene and save it (NewMap).
Choose Edit->Project Settings... and under "Maps & Modes" change the game/startup maps to 'NewMap'.
Under "Packaging" change the Blueprint Nativization Method to "Inclusive."
Choose File->Package Project->Windows->Win64, choose a location and wait for packaging to finish.
Note that cooking will fail with the given callstack.

Callstack

Assertion failed: bCreateInstance [File:D:\Build\++UE4+Release-4.19+Compile\Sync\Engine\Source\Developer\BlueprintCompilerCppBackend\Private\BlueprintCompilerCppBackendValueHelper.cpp] [Line: 2145]

UE4Editor_BlueprintCompilerCppBackend!FEmitDefaultValueHelper::HandleInstancedSubobject() [blueprintcompilercppbackendvaluehelper.cpp:2148]
UE4Editor_BlueprintCompilerCppBackend!FDefaultSubobjectData::EmitPropertyInitialization() [blueprintcompilercppbackendvaluehelper.cpp:828]
UE4Editor_BlueprintCompilerCppBackend!FEmitDefaultValueHelper::GenerateConstructor() [blueprintcompilercppbackendvaluehelper.cpp:1877]
UE4Editor_BlueprintCompilerCppBackend!FBlueprintCompilerCppBackendBase::GenerateCodeFromClass() [blueprintcompilercppbackendbase.cpp:445]
UE4Editor_KismetCompiler!FKismetCompilerContext::CompileFunctions() [kismetcompiler.cpp:4092]
UE4Editor_KismetCompiler!FKismet2CompilerModule::CompileBlueprintInner() [kismetcompilermodule.cpp:133]
UE4Editor_KismetCompiler!FKismet2CompilerModule::CompileBlueprint() [kismetcompilermodule.cpp:235]
UE4Editor_BlueprintNativeCodeGen!FBlueprintNativeCodeGenUtils::GenerateCppCode() [blueprintnativecodegenutils.cpp:456]
UE4Editor_BlueprintNativeCodeGen!FBlueprintNativeCodeGenModule::GenerateSingleAsset() [blueprintnativecodegenmodule.cpp:496]
UE4Editor_BlueprintNativeCodeGen!FBlueprintNativeCodeGenModule::GenerateFullyConvertedClasses() [blueprintnativecodegenmodule.cpp:398]
UE4Editor_UnrealEd!UCookOnTheFlyServer::CookByTheBookFinished() [cookontheflyserver.cpp:5440]
UE4Editor_UnrealEd!UCookOnTheFlyServer::TickCookOnTheSide() [cookontheflyserver.cpp:1829]
UE4Editor_UnrealEd!UCookCommandlet::CookByTheBook() [cookcommandlet.cpp:904]
UE4Editor_UnrealEd!UCookCommandlet::Main() [cookcommandlet.cpp:584]
UE4Editor_Cmd!FEngineLoop::PreInit() [launchengineloop.cpp:2195]
UE4Editor_Cmd!GuardedMain() [launch.cpp:127]
UE4Editor_Cmd!GuardedMainWrapper() [launchwindows.cpp:134]
UE4Editor_Cmd!WinMain() [launchwindows.cpp:210]
UE4Editor_Cmd!__scrt_common_main_seh() [exe_common.inl:253]
kernel32!BaseThreadInitThunk()
ntdll!RtlUserThreadStart()

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Fixed

Component	UE - Gameplay - Blueprint Compiler
Affects Versions	4.19
Target Fix	4.19.1

Fix Commit	3962782

Created	Mar 20, 2018
Resolved	Mar 23, 2018
Updated	Apr 27, 2018

View Jira Issue

UE-56316

[CrashReport] UE4Editor_BlueprintCompilerCppBackend!FEmitDefaultValueHelper::HandleInstancedSubobject() [blueprintcompilercppbackendvaluehelper.cpp:2148]

[CrashReport] UE4Editor_BlueprintCompilerCppBackend!FEmitDefaultValueHelper::HandleInstancedSubobject() [blueprintcompilercppbackendvaluehelper.cpp:2148]

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