// Copyright Epic Games, Inc. All Rights Reserved.

#include "Kismet2/KismetReinstanceUtilities.h"
#include "BlueprintCompilationManager.h"
#include "ComponentInstanceDataCache.h"
#include "Engine/Blueprint.h"
#include "Stats/StatsMisc.h"
#include "UObject/Package.h"
#include "Components/SceneComponent.h"
#include "GameFramework/Actor.h"
#include "Engine/World.h"
#include "Components/SkeletalMeshComponent.h"
#include "Components/ChildActorComponent.h"
#include "Animation/AnimInstance.h"
#include "Engine/Engine.h"
#include "Editor/EditorEngine.h"
#include "Animation/AnimBlueprint.h"
#include "Engine/BlueprintGeneratedClass.h"
#include "Engine/SimpleConstructionScript.h"
#include "FileHelpers.h"
#include "Kismet2/CompilerResultsLog.h"
#include "Kismet2/KismetEditorUtilities.h"
#include "Kismet2/BlueprintEditorUtils.h"
#include "Layers/LayersSubsystem.h"
#include "Editor.h"
#include "UObject/ReferencerFinder.h"

#include "UObject/UObjectHash.h"
#include "UObject/UObjectIterator.h"
#include "Serialization/FindObjectReferencers.h"
#include "Serialization/ArchiveReplaceObjectRef.h"  // @todo replace with ArchiveReplaceObjectAndStructPropertyRef.h in Main and remove FArchiveReplaceObjectAndStructPropertyRef below
#include "BlueprintEditor.h"
#include "Engine/Selection.h"
#include "BlueprintEditorSettings.h"
#include "Engine/NetDriver.h"
#include "Engine/ActorChannel.h"
#include "Subsystems/AssetEditorSubsystem.h"

// Enabling this will validate cached dependent Blueprints against the full set of loaded Blueprints when updating bytecode references.
// Note: Enabling this may potentially increase editor/Blueprint load time and/or decrease performance related to Blueprint compilation.
#ifndef VALIDATE_BYTECODE_REFERENCE_DEPENDENCY_CACHE
#define VALIDATE_BYTECODE_REFERENCE_DEPENDENCY_CACHE 0
#endif  // VALIDATE_BYTECODE_REFERENCE_DEPENDENCY_CACHE

DECLARE_CYCLE_STAT(TEXT("Replace Instances"), EKismetReinstancerStats_ReplaceInstancesOfClass, STATGROUP_KismetReinstancer);
DECLARE_CYCLE_STAT(TEXT("Find Referencers"), EKismetReinstancerStats_FindReferencers, STATGROUP_KismetReinstancer);
DECLARE_CYCLE_STAT(TEXT("Replace References"), EKismetReinstancerStats_ReplaceReferences, STATGROUP_KismetReinstancer);
DECLARE_CYCLE_STAT(TEXT("Construct Replacements"), EKismetReinstancerStats_ReplacementConstruction, STATGROUP_KismetReinstancer);
DECLARE_CYCLE_STAT(TEXT("Update Bytecode References"), EKismetReinstancerStats_UpdateBytecodeReferences, STATGROUP_KismetReinstancer);
DECLARE_CYCLE_STAT(TEXT("Recompile Child Classes"), EKismetReinstancerStats_RecompileChildClasses, STATGROUP_KismetReinstancer);
DECLARE_CYCLE_STAT(TEXT("Replace Classes Without Reinstancing"), EKismetReinstancerStats_ReplaceClassNoReinsancing, STATGROUP_KismetReinstancer);
DECLARE_CYCLE_STAT(TEXT("Reinstance Objects"), EKismetCompilerStats_ReinstanceObjects, STATGROUP_KismetCompiler);
DECLARE_CYCLE_STAT(TEXT("Refresh Dependent Blueprints In Reinstancer"), EKismetCompilerStats_RefreshDependentBlueprintsInReinstancer, STATGROUP_KismetCompiler);
DECLARE_CYCLE_STAT(TEXT("Recreate UberGraphPersistentFrame"), EKismetCompilerStats_RecreateUberGraphPersistentFrame, STATGROUP_KismetCompiler);

/*----------------------------------------------------------------------------
        FArchiveReplaceObjectAndStructPropertyRef.
----------------------------------------------------------------------------*/
/**
 * Specialized version of FArchiveReplaceObjectRef that replaces references to FFields
 * that were owned by any of the old UStructs in the Replacement Map with their respective
 * new versions that belong to the new UStrtucts in the Replacement Map.
 */
template <class T>
class FArchiveReplaceObjectAndStructPropertyRef: public FArchiveReplaceObjectRef<T>
{
public:
    /**
     * Initializes variables and starts the serialization search
     *
     * @param InSearchObject		The object to start the search on
     * @param InReplacementMap		Map of objects to find -> objects to replace them with (null zeros them)
     * @param bNullPrivateRefs		Whether references to non-public objects not contained within the SearchObject
     *								should be set to null
     * @param bIgnoreOuterRef		Whether we should replace Outer pointers on Objects.
     * @param bIgnoreArchetypeRef	Whether we should replace the ObjectArchetype reference on Objects.
     * @param bDelayStart			Specify true to prevent the constructor from starting the process.  Allows child classes' to do initialization stuff in their ctor
     */
    FArchiveReplaceObjectAndStructPropertyRef(
        UObject* InSearchObject,
        const TMap<T*, T*>& InReplacementMap,
        bool bNullPrivateRefs,
        bool bIgnoreOuterRef,
        bool bIgnoreArchetypeRef,
        bool bDelayStart                = false,
        bool bIgnoreClassGeneratedByRef = true)
        : FArchiveReplaceObjectRef<T>(InSearchObject, InReplacementMap, bNullPrivateRefs, bIgnoreOuterRef, bIgnoreArchetypeRef, bDelayStart, bIgnoreClassGeneratedByRef)
    {
    }

    /**
     * Serializes the reference to FProperties
     */
    virtual FArchive& operator<<(FField*& InField) override
    {
        if (InField)
        {
            // Some structs (like UFunctions in their bytecode) reference properties of another UStructs.
            // In this case we need to inspect their owner and if it's one of the objects we want to replace,
            // replace the entire property with the one matching on the struct we want to replace it with
            UStruct* OldOwnerStruct = InField->GetOwner<UStruct>();
            if (OldOwnerStruct)
            {
                T* const* ReplaceWith = (T* const*)((const TMap<UObject*, UObject*>*)&this->ReplacementMap)->Find(OldOwnerStruct);
                if (ReplaceWith)
                {
                    // We want to replace the property's owner but since that would be even worse than replacing UObject's Outer
                    // we need to replace the entire property instead. We need to find the new property on the object we want to replace the Owner with
                    UStruct* NewOwnerStruct  = CastChecked<UStruct>(*ReplaceWith);
                    FField* ReplaceWithField = NewOwnerStruct->FindPropertyByName(InField->GetFName());
                    // Do we need to verify the existence of ReplaceWithField? Theoretically it could be missing on the new version
                    // of the owner struct and in this case we still don't want to keep the stale old property pointer around so it's safer to null it
                    InField = ReplaceWithField;
                    this->ReplacedReferences.FindOrAdd(OldOwnerStruct).AddUnique(this->GetSerializedProperty());
                    this->Count++;
                }
                // A->IsIn(A) returns false, but we don't want to NULL that reference out, so extra check here.
                else if (OldOwnerStruct == this->SearchObject || OldOwnerStruct->IsIn(this->SearchObject))
                {
                    bool bAlreadyAdded = false;
                    this->SerializedObjects.Add(OldOwnerStruct, &bAlreadyAdded);
                    if (!bAlreadyAdded)
                    {
                        // No recursion
                        this->PendingSerializationObjects.Add(OldOwnerStruct);
                    }
                }
                else if (this->bNullPrivateReferences && !OldOwnerStruct->HasAnyFlags(RF_Public))
                {
                    checkf(false, TEXT("Can't null a reference to %s on property %s as it would be equivalent to nulling UObject's Outer."),
                           *OldOwnerStruct->GetPathName(), *InField->GetName());
                }
            }
            else
            {
                // Just serialize the field to find any UObjects it may be referencing that we want to replace
                InField->Serialize(*this);
            }
        }
        return *this;
    }
};

struct FReplaceReferenceHelper
{
    static void IncludeCDO(UClass* OldClass, UClass* NewClass, TMap<UObject*, UObject*>& OldToNewInstanceMap, TArray<UObject*>& SourceObjects, UObject* OriginalCDO)
    {
        UObject* OldCDO = OldClass->GetDefaultObject();
        UObject* NewCDO = NewClass->GetDefaultObject();

        // Add the old->new CDO mapping into the fixup map
        OldToNewInstanceMap.Add(OldCDO, NewCDO);
        // Add in the old CDO to this pass, so CDO references are fixed up
        SourceObjects.Add(OldCDO);

        if (OriginalCDO)
        {
            OldToNewInstanceMap.Add(OriginalCDO, NewCDO);
            SourceObjects.Add(OriginalCDO);
        }
    }

    static void IncludeClass(UClass* OldClass, UClass* NewClass, TMap<UObject*, UObject*>& OldToNewInstanceMap, TArray<UObject*>& SourceObjects, TArray<UObject*>& ObjectsToReplace)
    {
        OldToNewInstanceMap.Add(OldClass, NewClass);
        SourceObjects.Add(OldClass);

        if (UObject* OldCDO = OldClass->GetDefaultObject(false))
        {
            ObjectsToReplace.Add(OldCDO);
        }
    }

    static void FindAndReplaceReferences(const TArray<UObject*>& SourceObjects, TSet<UObject*>* ObjectsThatShouldUseOldStuff, const TArray<UObject*>& ObjectsToReplace, const TMap<UObject*, UObject*>& OldToNewInstanceMap, const TMap<FSoftObjectPath, UObject*>& ReinstancedObjectsWeakReferenceMap)
    {
        if (SourceObjects.Num() == 0 && ObjectsToReplace.Num() == 0)
        {
            return;
        }

        // Remember what values were in UActorChannel::Actor so we can restore them later (this should only affect reinstancing during PIE)
        // We need the old actor channel to tear down cleanly without affecting the new actor
        TMap<UActorChannel*, AActor*> ActorChannelActorRestorationMap;
        for (UActorChannel* ActorChannel: TObjectRange<UActorChannel>())
        {
            if (OldToNewInstanceMap.Contains(ActorChannel->Actor))
            {
                ActorChannelActorRestorationMap.Add(ActorChannel, ActorChannel->Actor);
            }
        }

        // Find everything that references these objects
        TArray<UObject*> Targets;
        {
            BP_SCOPED_COMPILER_EVENT_STAT(EKismetReinstancerStats_FindReferencers);

            Targets = FReferencerFinder::GetAllReferencers(SourceObjects, ObjectsThatShouldUseOldStuff);
        }

        {
            BP_SCOPED_COMPILER_EVENT_STAT(EKismetReinstancerStats_ReplaceReferences);

            for (UObject* Obj: Targets)
            {
                // Make sure we don't update properties in old objects, as they
                // may take ownership of objects referenced in new objects (e.g.
                // delete components owned by new actors)
                if (!ObjectsToReplace.Contains(Obj))
                {
                    // The class for finding and replacing weak references.
                    // We can't relay on "standard" weak references replacement as
                    // it depends on FSoftObjectPath::ResolveObject, which
                    // tries to find the object with the stored path. It is
                    // impossible, cause above we deleted old actors (after
                    // spawning new ones), so during objects traverse we have to
                    // find FSoftObjectPath with the raw given path taken
                    // before deletion of old actors and fix them.
                    class ReferenceReplace: public FArchiveReplaceObjectAndStructPropertyRef<UObject>
                    {
                    public:
                        ReferenceReplace(UObject* InSearchObject, const TMap<UObject*, UObject*>& InReplacementMap, const TMap<FSoftObjectPath, UObject*>& InWeakReferencesMap)
                            : FArchiveReplaceObjectAndStructPropertyRef<UObject>(InSearchObject, InReplacementMap, false, false, false, true), WeakReferencesMap(InWeakReferencesMap)
                        {
                            SerializeSearchObject();
                        }

                        FArchive& operator<<(FSoftObjectPath& Ref) override
                        {
                            const UObject* const* PtrToObjPtr = WeakReferencesMap.Find(Ref);

                            if (PtrToObjPtr != nullptr)
                            {
                                Ref = *PtrToObjPtr;
                            }

                            return *this;
                        }

                        FArchive& operator<<(FSoftObjectPtr& Ref) override
                        {
                            return operator<<(Ref.GetUniqueID());
                        }

                    private:
                        const TMap<FSoftObjectPath, UObject*>& WeakReferencesMap;
                    };

                    ReferenceReplace ReplaceAr(Obj, OldToNewInstanceMap, ReinstancedObjectsWeakReferenceMap);
                }
            }
        }

        // Restore the old UActorChannel::Actor values (undoing what the replace references archiver did above to them)
        for (const auto& KVP: ActorChannelActorRestorationMap)
        {
            KVP.Key->Actor = KVP.Value;
        }
    }
};

struct FArchetypeReinstanceHelper
{
    /** Returns the full set of archetypes rooted at a single archetype object, with additional object flags (optional) */
    static void GetArchetypeObjects(UObject* InObject, TArray<UObject*>& OutArchetypeObjects, EObjectFlags SubArchetypeFlags = RF_NoFlags)
    {
        OutArchetypeObjects.Empty();

        if (InObject != nullptr && InObject->HasAllFlags(RF_ArchetypeObject))
        {
            OutArchetypeObjects.Add(InObject);

            TArray<UObject*> ArchetypeInstances;
            InObject->GetArchetypeInstances(ArchetypeInstances);

            for (int32 Idx = 0; Idx < ArchetypeInstances.Num(); ++Idx)
            {
                UObject* ArchetypeInstance = ArchetypeInstances[Idx];
                if (ArchetypeInstance != nullptr && !ArchetypeInstance->IsPendingKill() && ArchetypeInstance->HasAllFlags(RF_ArchetypeObject | SubArchetypeFlags))
                {
                    OutArchetypeObjects.Add(ArchetypeInstance);

                    TArray<UObject*> SubArchetypeInstances;
                    ArchetypeInstance->GetArchetypeInstances(SubArchetypeInstances);

                    if (SubArchetypeInstances.Num() > 0)
                    {
                        ArchetypeInstances.Append(SubArchetypeInstances);
                    }
                }
            }
        }
    }

    /** Returns an object name that's found to be unique within the given set of archetype objects */
    static FName FindUniqueArchetypeObjectName(TArray<UObject*>& InArchetypeObjects)
    {
        FName OutName = NAME_None;

        if (InArchetypeObjects.Num() > 0)
        {
            while (OutName == NAME_None)
            {
                UObject* ArchetypeObject = InArchetypeObjects[0];
                OutName                  = MakeUniqueObjectName(ArchetypeObject->GetOuter(), ArchetypeObject->GetClass());
                for (int32 ObjIdx = 1; ObjIdx < InArchetypeObjects.Num(); ++ObjIdx)
                {
                    ArchetypeObject = InArchetypeObjects[ObjIdx];
                    if (StaticFindObjectFast(ArchetypeObject->GetClass(), ArchetypeObject->GetOuter(), OutName))
                    {
                        OutName = NAME_None;
                        break;
                    }
                }
            }
        }

        return OutName;
    }
};

FReplaceInstancesOfClassParameters::FReplaceInstancesOfClassParameters(UClass* InOldClass, UClass* InNewClass)
    : OldClass(InOldClass), NewClass(InNewClass), OriginalCDO(nullptr), ObjectsThatShouldUseOldStuff(nullptr), InstancesThatShouldUseOldClass(nullptr), bClassObjectReplaced(false), bPreserveRootComponent(true)
{
}

/////////////////////////////////////////////////////////////////////////////////
// FBlueprintCompileReinstancer

TSet<TWeakObjectPtr<UBlueprint>> FBlueprintCompileReinstancer::DependentBlueprintsToRefresh = TSet<TWeakObjectPtr<UBlueprint>>();
TSet<TWeakObjectPtr<UBlueprint>> FBlueprintCompileReinstancer::CompiledBlueprintsToSave     = TSet<TWeakObjectPtr<UBlueprint>>();

UClass* FBlueprintCompileReinstancer::HotReloadedOldClass                                   = nullptr;
UClass* FBlueprintCompileReinstancer::HotReloadedNewClass                                   = nullptr;

FBlueprintCompileReinstancer::FBlueprintCompileReinstancer(UClass* InClassToReinstance, EBlueprintCompileReinstancerFlags Flags)
    : ClassToReinstance(InClassToReinstance), DuplicatedClass(nullptr), OriginalCDO(nullptr), bHasReinstanced(false), ReinstClassType(RCT_Unknown), ClassToReinstanceDefaultValuesCRC(0), bIsRootReinstancer(false), bAllowResaveAtTheEndIfRequested(false)
{
    if (InClassToReinstance != nullptr && InClassToReinstance->ClassDefaultObject)
    {
        bool bAutoInferSaveOnCompile = !!(Flags & EBlueprintCompileReinstancerFlags::AutoInferSaveOnCompile);
        bool bIsBytecodeOnly         = !!(Flags & EBlueprintCompileReinstancerFlags::BytecodeOnly);
        bool bAvoidCDODuplication    = !!(Flags & EBlueprintCompileReinstancerFlags::AvoidCDODuplication);

        if (FKismetEditorUtilities::IsClassABlueprintSkeleton(ClassToReinstance))
        {
            ReinstClassType = RCT_BpSkeleton;
        }
        else if (ClassToReinstance->HasAnyClassFlags(CLASS_CompiledFromBlueprint))
        {
            ReinstClassType = RCT_BpGenerated;
        }
        else if (ClassToReinstance->HasAnyClassFlags(CLASS_Native))
        {
            ReinstClassType = RCT_Native;
        }
        bAllowResaveAtTheEndIfRequested        = bAutoInferSaveOnCompile && !bIsBytecodeOnly && (ReinstClassType != RCT_BpSkeleton);
        bUseDeltaSerializationToCopyProperties = !!(Flags & EBlueprintCompileReinstancerFlags::UseDeltaSerialization);

        SaveClassFieldMapping(InClassToReinstance);

        // Remember the initial CDO for the class being resinstanced
        OriginalCDO     = ClassToReinstance->GetDefaultObject();

        DuplicatedClass = MoveCDOToNewClass(ClassToReinstance, TMap<UClass*, UClass*>(), bAvoidCDODuplication);

        if (!bAvoidCDODuplication)
        {
            ensure(ClassToReinstance->ClassDefaultObject->GetClass() == DuplicatedClass);
            ClassToReinstance->ClassDefaultObject->Rename(nullptr, GetTransientPackage(), REN_DoNotDirty | REN_DontCreateRedirectors | REN_ForceNoResetLoaders);
        }

        // Note that we can't clear ClassToReinstance->ClassDefaultObject even though
        // we have moved it aside CleanAndSanitizeClass will want to grab the old CDO
        // so it can propagate values to the new one note that until that happens we are
        // in an extraordinary state: this class has a CDO of a different type

        ObjectsThatShouldUseOldStuff.Add(DuplicatedClass);  // CDO of REINST_ class can be used as archetype

        if (!bIsBytecodeOnly)
        {
            TArray<UObject*> ObjectsToChange;
            const bool bIncludeDerivedClasses = false;
            GetObjectsOfClass(ClassToReinstance, ObjectsToChange, bIncludeDerivedClasses);
            for (UObject* ObjectToChange: ObjectsToChange)
            {
                ObjectToChange->SetClass(DuplicatedClass);
            }

            TArray<UClass*> ChildrenOfClass;
            GetDerivedClasses(ClassToReinstance, ChildrenOfClass);
            for (UClass* ChildClass: ChildrenOfClass)
            {
                UBlueprint* ChildBP = Cast<UBlueprint>(ChildClass->ClassGeneratedBy);
                if (ChildBP)
                {
                    const bool bClassIsDirectlyGeneratedByTheBlueprint = (ChildBP->GeneratedClass == ChildClass) || (ChildBP->SkeletonGeneratedClass == ChildClass);

                    if (ChildBP->HasAnyFlags(RF_BeingRegenerated) || !bClassIsDirectlyGeneratedByTheBlueprint)
                    {
                        if (ChildClass->GetSuperClass() == ClassToReinstance)
                        {
                            ReparentChild(ChildClass);
                        }
                        else
                        {
                            ChildClass->AssembleReferenceTokenStream();
                            ChildClass->Bind();
                            ChildClass->StaticLink(true);
                        }

                        // TODO: some stronger condition would be nice
                        if (!bClassIsDirectlyGeneratedByTheBlueprint)
                        {
                            ObjectsThatShouldUseOldStuff.Add(ChildClass);
                        }
                    }
                    // If this is a direct child, change the parent and relink so the property chain is valid for reinstancing
                    else if (!ChildBP->HasAnyFlags(RF_NeedLoad))
                    {
                        if (ChildClass->GetSuperClass() == ClassToReinstance)
                        {
                            ReparentChild(ChildBP);
                        }

                        Children.AddUnique(ChildBP);
                    }
                    else
                    {
                        // If this is a child that caused the load of their parent, relink to the REINST class so that we can still serialize in the CDO, but do not add to later processing
                        ReparentChild(ChildClass);
                    }
                }
            }
        }

        // Pull the blueprint that generated this reinstance target, and gather the blueprints that are dependent on it
        UBlueprint* GeneratingBP = Cast<UBlueprint>(ClassToReinstance->ClassGeneratedBy);
        if (!IsReinstancingSkeleton() && GeneratingBP)
        {
            ClassToReinstanceDefaultValuesCRC = GeneratingBP->CrcLastCompiledCDO;

            // Never queue for saving when regenerating on load
            if (!GeneratingBP->bIsRegeneratingOnLoad && !IsReinstancingSkeleton())
            {
                bool const bIsLevelPackage = (UWorld::FindWorldInPackage(GeneratingBP->GetOutermost()) != nullptr);
                // we don't want to save the entire level (especially if this
                // compile was already kicked off as a result of a level save, as it
                // could cause a recursive save)... let the "SaveOnCompile" setting
                // only save blueprint assets
                if (!bIsLevelPackage)
                {
                    CompiledBlueprintsToSave.Add(GeneratingBP);
                }
            }
        }
    }
}

void FBlueprintCompileReinstancer::SaveClassFieldMapping(UClass* InClassToReinstance)
{
    check(InClassToReinstance);

    for (FProperty* Prop = InClassToReinstance->PropertyLink; Prop && (Prop->GetOwner<UObject>() == InClassToReinstance); Prop = Prop->PropertyLinkNext)
    {
        PropertyMap.Add(Prop->GetFName(), Prop);
    }

    for (UFunction* Function: TFieldRange<UFunction>(InClassToReinstance, EFieldIteratorFlags::ExcludeSuper))
    {
        FunctionMap.Add(Function->GetFName(), Function);
    }
}

void FBlueprintCompileReinstancer::GenerateFieldMappings(TMap<FFieldVariant, FFieldVariant>& FieldMapping)
{
    check(ClassToReinstance);

    FieldMapping.Empty();

    for (TPair<FName, FProperty*>& Prop: PropertyMap)
    {
        FieldMapping.Add(Prop.Value, FindFProperty<FProperty>(ClassToReinstance, *Prop.Key.ToString()));
    }

    for (TPair<FName, UFunction*>& Func: FunctionMap)
    {
        UFunction* NewFunction = ClassToReinstance->FindFunctionByName(Func.Key, EIncludeSuperFlag::ExcludeSuper);
        FieldMapping.Add(Func.Value, NewFunction);
    }

    UObject* NewCDO = ClassToReinstance->GetDefaultObject();
    FieldMapping.Add(OriginalCDO, NewCDO);
}

void FBlueprintCompileReinstancer::AddReferencedObjects(FReferenceCollector& Collector)
{
    Collector.AllowEliminatingReferences(false);
    Collector.AddReferencedObject(OriginalCDO);
    Collector.AddReferencedObject(DuplicatedClass);
    Collector.AllowEliminatingReferences(true);

    // it's ok for these to get GC'd, but it is not ok for the memory to be reused (after a GC),
    // for that reason we cannot allow these to be freed during the life of this reinstancer
    //
    // for example, we saw this as a problem in UpdateBytecodeReferences() - if the GC'd function
    // memory was used for a new (unrelated) function, then we were replacing references to the
    // new function (bad), as well as any old stale references (both were using the same memory address)
    Collector.AddReferencedObjects(FunctionMap);
    for (TPair<FName, FProperty*>& PropertyNamePair: PropertyMap)
    {
        if (PropertyNamePair.Value)
        {
            PropertyNamePair.Value->AddReferencedObjects(Collector);
        }
    }
}

void FBlueprintCompileReinstancer::OptionallyRefreshNodes(UBlueprint* CurrentBP)
{
    if (HotReloadedNewClass)
    {
        UPackage* const Package               = CurrentBP->GetOutermost();
        const bool bStartedWithUnsavedChanges = Package != nullptr ? Package->IsDirty() : true;

        FBlueprintEditorUtils::RefreshExternalBlueprintDependencyNodes(CurrentBP, HotReloadedNewClass);

        if (Package != nullptr && Package->IsDirty() && !bStartedWithUnsavedChanges)
        {
            Package->SetDirtyFlag(false);
        }
    }
}

FBlueprintCompileReinstancer::~FBlueprintCompileReinstancer()
{
    if (bIsRootReinstancer && bAllowResaveAtTheEndIfRequested)
    {
        if (CompiledBlueprintsToSave.Num() > 0)
        {
            if (!IsRunningCommandlet() && !GIsAutomationTesting)
            {
                TArray<UPackage*> PackagesToSave;
                for (TWeakObjectPtr<UBlueprint> BPPtr: CompiledBlueprintsToSave)
                {
                    if (BPPtr.IsValid())
                    {
                        UBlueprint* BP                     = BPPtr.Get();

                        UBlueprintEditorSettings* Settings = GetMutableDefault<UBlueprintEditorSettings>();
                        const bool bShouldSaveOnCompile    = ((Settings->SaveOnCompile == SoC_Always) || ((Settings->SaveOnCompile == SoC_SuccessOnly) && (BP->Status == BS_UpToDate)));

                        if (bShouldSaveOnCompile)
                        {
                            PackagesToSave.Add(BP->GetOutermost());
                        }
                    }
                }

                FEditorFileUtils::PromptForCheckoutAndSave(PackagesToSave, /*bCheckDirty =*/true, /*bPromptToSave =*/false);
            }
            CompiledBlueprintsToSave.Empty();
        }
    }
}

class FReinstanceFinalizer: public TSharedFromThis<FReinstanceFinalizer>
{
public:
    TSharedPtr<FBlueprintCompileReinstancer> Reinstancer;
    TArray<UObject*> ObjectsToReplace;
    TArray<UObject*> ObjectsToFinalize;
    TSet<UObject*> SelectedObjecs;
    UClass* ClassToReinstance;

    FReinstanceFinalizer(UClass* InClassToReinstance): ClassToReinstance(InClassToReinstance)
    {
        check(ClassToReinstance);
    }

    void Finalize()
    {
        if (!ensure(Reinstancer.IsValid()))
        {
            return;
        }
        check(ClassToReinstance);

        const bool bIsActor = ClassToReinstance->IsChildOf<AActor>();
        if (bIsActor)
        {
            for (UObject* Obj: ObjectsToFinalize)
            {
                AActor* Actor = CastChecked<AActor>(Obj);

                UWorld* World = Actor->GetWorld();
                if (World)
                {
                    // Remove any pending latent actions, as the compiled script code may have changed, and thus the
                    // cached LinkInfo data may now be invalid. This could happen in the fast path, since the original
                    // Actor instance will not be replaced in that case, and thus might still have latent actions pending.
                    World->GetLatentActionManager().RemoveActionsForObject(Actor);

                    // Drop any references to anim script components for skeletal mesh components, depending on how
                    // the blueprints have changed during compile this could contain invalid data so we need to do
                    // a full initialisation to ensure everything is set up correctly.
                    TInlineComponentArray<USkeletalMeshComponent*> SkelComponents(Actor);
                    for (USkeletalMeshComponent* SkelComponent: SkelComponents)
                    {
                        SkelComponent->AnimScriptInstance = nullptr;
                    }

                    Actor->ReregisterAllComponents();
                    Actor->RerunConstructionScripts();

                    // The reinstancing case doesn't ever explicitly call Actor->FinishSpawning, we've handled the construction script
                    // portion above but still need the PostActorConstruction() case so BeginPlay gets routed correctly while in a BegunPlay world
                    if (World->HasBegunPlay())
                    {
                        Actor->PostActorConstruction();
                    }

                    if (SelectedObjecs.Contains(Obj) && GEditor)
                    {
                        GEditor->SelectActor(Actor, /*bInSelected =*/true, /*bNotify =*/true, false, true);
                    }
                }
            }
        }

        const bool bIsAnimInstance = ClassToReinstance->IsChildOf<UAnimInstance>();
        // UAnimBlueprintGeneratedClass* AnimClass = Cast<UAnimBlueprintGeneratedClass>(ClassToReinstance);
        if (bIsAnimInstance)
        {
            for (UObject* Obj: ObjectsToFinalize)
            {
                if (USkeletalMeshComponent* SkelComponent = Cast<USkeletalMeshComponent>(Obj->GetOuter()))
                {
                    // This snippet catches all of the exposed value handlers that will have invalid UFunctions
                    // and clears the init flag so they will be reinitialized on the next call to InitAnim.
                    // Unknown whether there are other unreachable properties so currently clearing the anim
                    // instance below
                    // #TODO investigate reinstancing anim blueprints to correctly catch all deep references

                    // UAnimInstance* ActiveInstance = SkelComponent->GetAnimInstance();
                    // if(AnimClass && ActiveInstance)
                    //{
                    //	for(FStructProperty* NodeProp : AnimClass->AnimNodeProperties)
                    //	{
                    //		// Guaranteed to have only FAnimNode_Base pointers added during compilation
                    //		FAnimNode_Base* AnimNode = NodeProp->ContainerPtrToValuePtr<FAnimNode_Base>(ActiveInstance);
                    //
                    //		AnimNode->EvaluateGraphExposedInputs.bInitialized = false;
                    //	}
                    // }

                    // Clear out the script instance on the component to force a rebuild during initialization.
                    // This is necessary to correctly reinitialize certain properties that still reference the
                    // old class as they are unreachable during reinstancing.
                    SkelComponent->AnimScriptInstance = nullptr;
                    SkelComponent->InitAnim(true);
                }
            }
        }

        Reinstancer->FinalizeFastReinstancing(ObjectsToReplace);
    }
};

TSharedPtr<FReinstanceFinalizer> FBlueprintCompileReinstancer::ReinstanceFast()
{
    UE_LOG(LogBlueprint, Log, TEXT("BlueprintCompileReinstancer: Doing a fast path refresh on class '%s'."), *GetPathNameSafe(ClassToReinstance));

    TSharedPtr<FReinstanceFinalizer> Finalizer = MakeShareable(new FReinstanceFinalizer(ClassToReinstance));
    Finalizer->Reinstancer                     = SharedThis(this);

    GetObjectsOfClass(DuplicatedClass, Finalizer->ObjectsToReplace, /*bIncludeDerivedClasses=*/false);

    const bool bIsActor     = ClassToReinstance->IsChildOf<AActor>();
    const bool bIsComponent = ClassToReinstance->IsChildOf<UActorComponent>();
    for (UObject* Obj: Finalizer->ObjectsToReplace)
    {
        UE_LOG(LogBlueprint, Log, TEXT("  Fast path is refreshing (not replacing) %s"), *Obj->GetFullName());

        const bool bIsChildActorTemplate = (bIsActor ? CastChecked<AActor>(Obj)->GetOuter()->IsA<UChildActorComponent>() : false);
        if ((!Obj->IsTemplate() || bIsComponent || bIsChildActorTemplate) && !Obj->IsPendingKill())
        {
            if (bIsActor && Obj->IsSelected())
            {
                Finalizer->SelectedObjecs.Add(Obj);
            }

            Obj->SetClass(ClassToReinstance);

            Finalizer->ObjectsToFinalize.Push(Obj);
        }
    }

    return Finalizer;
}

void FBlueprintCompileReinstancer::FinalizeFastReinstancing(TArray<UObject*>& ObjectsToReplace)
{
    TArray<UObject*> SourceObjects;
    TMap<UObject*, UObject*> OldToNewInstanceMap;
    TMap<FSoftObjectPath, UObject*> ReinstancedObjectsWeakReferenceMap;
    FReplaceReferenceHelper::IncludeCDO(DuplicatedClass, ClassToReinstance, OldToNewInstanceMap, SourceObjects, OriginalCDO);

    if (IsClassObjectReplaced())
    {
        FReplaceReferenceHelper::IncludeClass(DuplicatedClass, ClassToReinstance, OldToNewInstanceMap, SourceObjects, ObjectsToReplace);
    }

    FReplaceReferenceHelper::FindAndReplaceReferences(SourceObjects, &ObjectsThatShouldUseOldStuff, ObjectsToReplace, OldToNewInstanceMap, ReinstancedObjectsWeakReferenceMap);

    if (ClassToReinstance->IsChildOf<UActorComponent>())
    {
        // ReplaceInstancesOfClass() handles this itself, if we had to re-instance
        ReconstructOwnerInstances(ClassToReinstance);
    }
}

void FBlueprintCompileReinstancer::CompileChildren()
{
    BP_SCOPED_COMPILER_EVENT_STAT(EKismetReinstancerStats_RecompileChildClasses);

    // Reparent all dependent blueprints, and recompile to ensure that they get reinstanced with the new memory layout
    for (UBlueprint* BP: Children)
    {
        if (BP->ParentClass == ClassToReinstance || BP->ParentClass == DuplicatedClass)
        {
            ReparentChild(BP);

            // avoid the skeleton compile if we don't need it - if the class
            // we're reinstancing is a Blueprint class, then we assume sub-class
            // skeletons were kept in-sync (updated/reinstanced when the parent
            // was updated); however, if this is a native class (like when hot-
            // reloading), then we want to make sure to update the skel as well
            EBlueprintCompileOptions Options = EBlueprintCompileOptions::SkipGarbageCollection;
            if (!ClassToReinstance->HasAnyClassFlags(CLASS_Native))
            {
                Options |= EBlueprintCompileOptions::SkeletonUpToDate;
            }
            FKismetEditorUtilities::CompileBlueprint(BP, Options);
        }
        else if (IsReinstancingSkeleton())
        {
            const bool bForceRegeneration = true;
            FKismetEditorUtilities::GenerateBlueprintSkeleton(BP, bForceRegeneration);
        }
    }
}

TSharedPtr<FReinstanceFinalizer> FBlueprintCompileReinstancer::ReinstanceInner(bool bForceAlwaysReinstance)
{
    TSharedPtr<FReinstanceFinalizer> Finalizer;
    if (ClassToReinstance && DuplicatedClass)
    {
        static const FBoolConfigValueHelper ReinstanceOnlyWhenNecessary(TEXT("Kismet"), TEXT("bReinstanceOnlyWhenNecessary"), GEngineIni);
        bool bShouldReinstance = true;
        // See if we need to do a full reinstance or can do the faster refresh path (when enabled or no values were modified, and the structures match)
        if (ReinstanceOnlyWhenNecessary && !bForceAlwaysReinstance)
        {
            BP_SCOPED_COMPILER_EVENT_STAT(EKismetReinstancerStats_ReplaceClassNoReinsancing);

            const UBlueprintGeneratedClass* BPClassA = Cast<const UBlueprintGeneratedClass>(DuplicatedClass);
            const UBlueprintGeneratedClass* BPClassB = Cast<const UBlueprintGeneratedClass>(ClassToReinstance);
            const UBlueprint* BP                     = Cast<const UBlueprint>(ClassToReinstance->ClassGeneratedBy);

            const bool bTheSameDefaultValues         = (BP != nullptr) && (ClassToReinstanceDefaultValuesCRC != 0) && (BP->CrcLastCompiledCDO == ClassToReinstanceDefaultValuesCRC);
            const bool bTheSameLayout                = (BPClassA != nullptr) && (BPClassB != nullptr) && FStructUtils::TheSameLayout(BPClassA, BPClassB, true);
            const bool bAllowedToDoFastPath          = bTheSameDefaultValues && bTheSameLayout;
            if (bAllowedToDoFastPath)
            {
                Finalizer         = ReinstanceFast();
                bShouldReinstance = false;
            }
        }

        if (bShouldReinstance)
        {
            UE_LOG(LogBlueprint, Log, TEXT("BlueprintCompileReinstancer: Doing a full reinstance on class '%s'"), *GetPathNameSafe(ClassToReinstance));
            ReplaceInstancesOfClass(DuplicatedClass, ClassToReinstance, OriginalCDO, &ObjectsThatShouldUseOldStuff, IsClassObjectReplaced(), ShouldPreserveRootComponentOfReinstancedActor());
        }
    }
    return Finalizer;
}

void FBlueprintCompileReinstancer::ListDependentBlueprintsToRefresh(const TArray<UBlueprint*>& DependentBPs)
{
    for (UBlueprint* Element: DependentBPs)
    {
        DependentBlueprintsToRefresh.Add(Element);
    }
}

void FBlueprintCompileReinstancer::EnlistDependentBlueprintToRecompile(UBlueprint* BP, bool bBytecodeOnly)
{
}

void FBlueprintCompileReinstancer::BlueprintWasRecompiled(UBlueprint* BP, bool bBytecodeOnly)
{
    if (IsValid(BP))
    {
        DependentBlueprintsToRefresh.Remove(BP);
    }
}

extern UNREALED_API FSecondsCounterData BlueprintCompileAndLoadTimerData;

void FBlueprintCompileReinstancer::ReinstanceObjects(bool bForceAlwaysReinstance)
{
    FSecondsCounterScope Timer(BlueprintCompileAndLoadTimerData);

    BP_SCOPED_COMPILER_EVENT_STAT(EKismetCompilerStats_ReinstanceObjects);

    // Make sure we only reinstance classes once!
    static TArray<TSharedRef<FBlueprintCompileReinstancer>> QueueToReinstance;

    if (!bHasReinstanced)
    {
        TSharedRef<FBlueprintCompileReinstancer> SharedThis = AsShared();
        bool bAlreadyQueued                                 = QueueToReinstance.Contains(SharedThis);

        // We may already be reinstancing this class, this happens when a dependent blueprint has a compile error and we try to reinstance the stub:
        if (!bAlreadyQueued)
        {
            for (const TSharedRef<FBlueprintCompileReinstancer>& Entry: QueueToReinstance)
            {
                if (Entry->ClassToReinstance == SharedThis->ClassToReinstance)
                {
                    bAlreadyQueued = true;
                    break;
                }
            }
        }

        if (!bAlreadyQueued)
        {
            QueueToReinstance.Push(SharedThis);

            if (ClassToReinstance && DuplicatedClass)
            {
                CompileChildren();
            }

            if (QueueToReinstance.Num() && (QueueToReinstance[0] == SharedThis))
            {
                // Mark it as the source reinstancer, no other reinstancer can get here until this Blueprint finishes compiling
                bIsRootReinstancer = true;

                if (!IsReinstancingSkeleton())
                {
                    TGuardValue<bool> ReinstancingGuard(GIsReinstancing, true);

                    TArray<TSharedPtr<FReinstanceFinalizer>> Finalizers;

                    // All children were recompiled. It's safe to reinstance.
                    for (int32 Idx = 0; Idx < QueueToReinstance.Num(); ++Idx)
                    {
                        TSharedPtr<FReinstanceFinalizer> Finalizer = QueueToReinstance[Idx]->ReinstanceInner(bForceAlwaysReinstance);
                        if (Finalizer.IsValid())
                        {
                            Finalizers.Push(Finalizer);
                        }
                        QueueToReinstance[Idx]->bHasReinstanced = true;
                    }
                    QueueToReinstance.Empty();

                    for (TSharedPtr<FReinstanceFinalizer>& Finalizer: Finalizers)
                    {
                        if (Finalizer.IsValid())
                        {
                            Finalizer->Finalize();
                        }
                    }

                    {
                        BP_SCOPED_COMPILER_EVENT_STAT(EKismetCompilerStats_RefreshDependentBlueprintsInReinstancer);
                        for (TWeakObjectPtr<UBlueprint>& BPPtr: DependentBlueprintsToRefresh)
                        {
                            if (BPPtr.IsValid())
                            {
                                BPPtr->BroadcastChanged();
                            }
                        }
                        DependentBlueprintsToRefresh.Empty();
                    }

                    if (GEditor)
                    {
                        GEditor->BroadcastBlueprintCompiled();
                    }
                }
                else
                {
                    QueueToReinstance.Empty();
                    DependentBlueprintsToRefresh.Empty();
                }
            }
        }
    }
}

class FArchiveReplaceFieldReferences: public FArchiveReplaceObjectRefBase
{
public:
    /**
     * Initializes variables and starts the serialization search
     *
     * @param InSearchObject		The object to start the search on
     * @param ReplacementMap		Map of objects to find -> objects to replace them with (null zeros them)
     * @param bNullPrivateRefs		Whether references to non-public objects not contained within the SearchObject
     *								should be set to null
     * @param bIgnoreOuterRef		Whether we should replace Outer pointers on Objects.
     * @param bIgnoreArchetypeRef	Whether we should replace the ObjectArchetype reference on Objects.
     * @param bDelayStart			Specify true to prevent the constructor from starting the process.  Allows child classes' to do initialization stuff in their ctor
     */
    FArchiveReplaceFieldReferences(
        UObject* InSearchObject,
        const TMap<FFieldVariant, FFieldVariant>& InReplacementMap,
        bool bNullPrivateRefs,
        bool bIgnoreOuterRef,
        bool bIgnoreArchetypeRef,
        bool bDelayStart                = false,
        bool bIgnoreClassGeneratedByRef = true)
        : ReplacementMap(InReplacementMap)
    {
        SearchObject                         = InSearchObject;
        Count                                = 0;
        bNullPrivateReferences               = bNullPrivateRefs;

        ArIsObjectReferenceCollector         = true;
        ArIsModifyingWeakAndStrongReferences = true;  // Also replace weak references too!
        ArIgnoreArchetypeRef                 = bIgnoreArchetypeRef;
        ArIgnoreOuterRef                     = bIgnoreOuterRef;
        ArIgnoreClassGeneratedByRef          = bIgnoreClassGeneratedByRef;

        if (!bDelayStart)
        {
            SerializeSearchObject();
        }
    }

    /**
     * Starts the serialization of the root object
     */
    void SerializeSearchObject()
    {
        ReplacedReferences.Empty();

        if (SearchObject != NULL && !SerializedObjects.Find(SearchObject) && (ReplacementMap.Num() > 0 || bNullPrivateReferences))
        {
            // start the initial serialization
            SerializedObjects.Add(SearchObject);
            SerializeObject(SearchObject);
            for (int32 Iter = 0; Iter < PendingSerializationObjects.Num(); Iter++)
            {
                SerializeObject(PendingSerializationObjects[Iter]);
            }
            PendingSerializationObjects.Reset();
        }
    }

    /**
     * Serializes the reference to the object
     */
    virtual FArchive& operator<<(UObject*& Obj) override
    {
        if (Obj != nullptr)
        {
            // If these match, replace the reference
            const FFieldVariant* ReplaceWith = ReplacementMap.Find(Obj);
            if (ReplaceWith != nullptr)
            {
                Obj = ReplaceWith->ToUObject();
                ReplacedReferences.FindOrAdd(Obj).AddUnique(GetSerializedProperty());
                Count++;
            }
            // A->IsIn(A) returns false, but we don't want to NULL that reference out, so extra check here.
            else if (Obj == SearchObject || Obj->IsIn(SearchObject))
            {
#if 0
				// DEBUG: Log when we are using the A->IsIn(A) path here.
				if (Obj == SearchObject)
				{
					FString ObjName = Obj->GetPathName();
					UE_LOG(LogSerialization, Log, TEXT("FArchiveReplaceObjectRef: Obj == SearchObject : '%s'"), *ObjName);
				}
#endif
                bool bAlreadyAdded = false;
                SerializedObjects.Add(Obj, &bAlreadyAdded);
                if (!bAlreadyAdded)
                {
                    // No recursion
                    PendingSerializationObjects.Add(Obj);
                }
            }
            else if (bNullPrivateReferences && !Obj->HasAnyFlags(RF_Public))
            {
                Obj = nullptr;
            }
        }
        return *this;
    }

    /**
     * Serializes the reference to a field
     */
    virtual FArchive& operator<<(FField*& Field) override
    {
        if (Field != nullptr)
        {
            // If these match, replace the reference
            const FFieldVariant* ReplaceWith = ReplacementMap.Find(Field);
            if (ReplaceWith != nullptr)
            {
                Field = ReplaceWith->ToField();
                // ReplacedReferences.FindOrAdd(Obj).AddUnique(GetSerializedProperty());
                Count++;
            }
        }
        return *this;
    }

protected:
    /** Map of objects to find references to -> object to replace references with */
    const TMap<FFieldVariant, FFieldVariant>& ReplacementMap;
};

void FBlueprintCompileReinstancer::UpdateBytecodeReferences()
{
    BP_SCOPED_COMPILER_EVENT_STAT(EKismetReinstancerStats_UpdateBytecodeReferences);

    if (!ClassToReinstance)
    {
        return;
    }

    if (UBlueprint* CompiledBlueprint = UBlueprint::GetBlueprintFromClass(ClassToReinstance))
    {
        TMap<FFieldVariant, FFieldVariant> FieldMappings;
        GenerateFieldMappings(FieldMappings);

        // Note: This API returns a cached set of blueprints that's updated at compile time.
        TArray<UBlueprint*> CachedDependentBPs;
        FBlueprintEditorUtils::GetDependentBlueprints(CompiledBlueprint, CachedDependentBPs);

        // Determine whether or not we will be updating references for an Animation Blueprint class.
        const bool bIsAnimBlueprintClass = !!Cast<UAnimBlueprint>(ClassToReinstance->ClassGeneratedBy);

#if VALIDATE_BYTECODE_REFERENCE_DEPENDENCY_CACHE
        TArray<UBlueprint*> ActualDependentBPs;
        for (TObjectIterator<UBlueprint> BpIt; BpIt; ++BpIt)
#else
        for (auto BpIt = CachedDependentBPs.CreateIterator(); BpIt; ++BpIt)
#endif  // VALIDATE_BYTECODE_REFERENCE_DEPENDENCY_CACHE
        {
            UBlueprint* DependentBP = *BpIt;
            UClass* BPClass         = DependentBP->GeneratedClass;

            // Skip cases where the class is junk, or haven't finished serializing in yet
            // Note that BPClass can be null for blueprints that can no longer be compiled:
            if (!BPClass || (BPClass == ClassToReinstance) || (BPClass->GetOutermost() == GetTransientPackage()) || BPClass->HasAnyClassFlags(CLASS_NewerVersionExists) || (BPClass->ClassGeneratedBy && BPClass->ClassGeneratedBy->HasAnyFlags(RF_NeedLoad | RF_BeingRegenerated)))
            {
                continue;
            }

            BPClass->ClearFunctionMapsCaches();

            // Ensure that Animation Blueprint child class dependencies are always re-linked, as the child may reference properties generated during
            // compilation of the parent class, which will have shifted to a TRASHCLASS Outer at this point (see UAnimBlueprintGeneratedClass::Link()).
            if (bIsAnimBlueprintClass && BPClass->IsChildOf(ClassToReinstance))
            {
                BPClass->StaticLink(true);
            }

            bool bBPWasChanged = false;
            // For each function defined in this blueprint, run through the bytecode, and update any refs from the old properties to the new
            for (TFieldIterator<UFunction> FuncIter(BPClass, EFieldIteratorFlags::ExcludeSuper); FuncIter; ++FuncIter)
            {
                UFunction* CurrentFunction = *FuncIter;
                FArchiveReplaceFieldReferences ReplaceAr(CurrentFunction, FieldMappings, /*bNullPrivateRefs=*/false, /*bIgnoreOuterRef=*/true, /*bIgnoreArchetypeRef=*/true);
                bBPWasChanged |= (0 != ReplaceAr.GetCount());
            }

            // Update any refs in called functions array, as the bytecode was just similarly updated:
            if (UBlueprintGeneratedClass* AsBPGC = Cast<UBlueprintGeneratedClass>(BPClass))
            {
                for (int32 Idx = 0; Idx < AsBPGC->CalledFunctions.Num(); ++Idx)
                {
                    FFieldVariant* Val = FieldMappings.Find(AsBPGC->CalledFunctions[Idx]);
                    if (Val && Val->IsValid())
                    {
                        // This ::Cast should always succeed, but I'm uncomfortable making
                        // rigid assumptions about the FieldMappings array:
                        if (UFunction* NewFn = Val->Get<UFunction>())
                        {
                            AsBPGC->CalledFunctions[Idx] = NewFn;
                        }
                    }
                }
            }

            FArchiveReplaceFieldReferences ReplaceInBPAr(DependentBP, FieldMappings, false, true, true);
            if (ReplaceInBPAr.GetCount())
            {
#if VALIDATE_BYTECODE_REFERENCE_DEPENDENCY_CACHE
                ActualDependentBPs.Add(DependentBP);
#endif  // VALIDATE_BYTECODE_REFERENCE_DEPENDENCY_CACHE

                bBPWasChanged = true;
                UE_LOG(LogBlueprint, Log, TEXT("UpdateBytecodeReferences: %d references from %s was replaced in BP %s"), ReplaceInBPAr.GetCount(), *GetPathNameSafe(ClassToReinstance), *GetPathNameSafe(DependentBP));
            }

            if (bBPWasChanged && CompiledBlueprint && !CompiledBlueprint->bIsRegeneratingOnLoad)
            {
                DependentBlueprintsToRefresh.Add(DependentBP);
            }
        }

#if VALIDATE_BYTECODE_REFERENCE_DEPENDENCY_CACHE
        bool bHasMissingDependents = false;
        for (UBlueprint* ChangedBP: ActualDependentBPs)
        {
            if (!CachedDependentBPs.Contains(ChangedBP))
            {
                UE_LOG(LogBlueprint, Error, TEXT("While updating %s, we needed to update %s but it wasn't cached as a dependent"), *ClassToReinstance->GetName(), *ChangedBP->GetName());
                bHasMissingDependents = true;
            }
        }

        if (bHasMissingDependents)
        {
            UE_LOG(LogBlueprint, Error, TEXT("Class: %s, CachedDeps: [%s], ActualDeps: [%s]"),
                   *ClassToReinstance->GetName(),
                   *FString::JoinBy(CachedDependentBPs, TEXT(","), [](UBlueprint* Blueprint)
                                    {
                                        return Blueprint->GetName();
                                    }),
                   *FString::JoinBy(ActualDependentBPs, TEXT(","), [](UBlueprint* Blueprint)
                                    {
                                        return Blueprint->GetName();
                                    }));
        }
#endif  // VALIDATE_BYTECODE_REFERENCE_DEPENDENCY_CACHE
    }
}

/** Lots of redundancy with ReattachActorsHelper */
struct FAttachedActorInfo
{
    FAttachedActorInfo()
        : AttachedActor(nullptr), AttachedToSocket()
    {
    }

    AActor* AttachedActor;
    FName AttachedToSocket;
};

struct FActorAttachmentData
{
    FActorAttachmentData();
    FActorAttachmentData(AActor* OldActor);
    FActorAttachmentData(const FActorAttachmentData&)            = default;
    FActorAttachmentData& operator=(const FActorAttachmentData&) = default;
    FActorAttachmentData(FActorAttachmentData&&)                 = default;
    FActorAttachmentData& operator=(FActorAttachmentData&&)      = default;
    ~FActorAttachmentData()                                      = default;

    AActor* TargetAttachParent;
    USceneComponent* TargetParentComponent;
    FName TargetAttachSocket;

    TArray<FAttachedActorInfo> PendingChildAttachments;
};

FActorAttachmentData::FActorAttachmentData()
    : TargetAttachParent(nullptr), TargetParentComponent(nullptr), TargetAttachSocket(), PendingChildAttachments()
{
}

FActorAttachmentData::FActorAttachmentData(AActor* OldActor)
{
    TargetAttachParent    = nullptr;
    TargetParentComponent = nullptr;

    TArray<AActor*> AttachedActors;
    OldActor->GetAttachedActors(AttachedActors);

    // if there are attached objects detach them and store the socket names
    for (AActor* AttachedActor: AttachedActors)
    {
        USceneComponent* AttachedActorRoot = AttachedActor->GetRootComponent();
        if (AttachedActorRoot && AttachedActorRoot->GetAttachParent())
        {
            // Save info about actor to reattach
            FAttachedActorInfo Info;
            Info.AttachedActor    = AttachedActor;
            Info.AttachedToSocket = AttachedActorRoot->GetAttachSocketName();
            PendingChildAttachments.Add(Info);
        }
    }

    if (USceneComponent* OldRootComponent = OldActor->GetRootComponent())
    {
        if (OldRootComponent->GetAttachParent() != nullptr)
        {
            TargetAttachParent = OldRootComponent->GetAttachParent()->GetOwner();
            // Root component should never be attached to another component in the same actor!
            if (TargetAttachParent == OldActor)
            {
                UE_LOG(LogBlueprint, Warning, TEXT("ReplaceInstancesOfClass: RootComponent (%s) attached to another component in this Actor (%s)."), *OldRootComponent->GetPathName(), *TargetAttachParent->GetPathName());
                TargetAttachParent = nullptr;
            }

            TargetAttachSocket    = OldRootComponent->GetAttachSocketName();
            TargetParentComponent = OldRootComponent->GetAttachParent();
        }
    }
}

/**
 * Utility struct that represents a single replacement actor. Used to cache off
 * attachment info for the old actor (the one being replaced), that will be
 * used later for the new actor (after all instances have been replaced).
 */
struct FActorReplacementHelper
{
    /** NOTE: this detaches OldActor from all child/parent attachments. */
    FActorReplacementHelper(AActor* InNewActor, AActor* OldActor, FActorAttachmentData&& InAttachmentData)
        : NewActor(InNewActor), TargetWorldTransform(FTransform::Identity), AttachmentData(MoveTemp(InAttachmentData)), bSelectNewActor(OldActor->IsSelected())
    {
        CachedActorData = StaticCastSharedPtr<AActor::FActorTransactionAnnotation>(OldActor->FindOrCreateTransactionAnnotation());
        TArray<AActor*> AttachedActors;
        OldActor->GetAttachedActors(AttachedActors);

        // if there are attached objects detach them and store the socket names
        for (AActor* AttachedActor: AttachedActors)
        {
            USceneComponent* AttachedActorRoot = AttachedActor->GetRootComponent();
            if (AttachedActorRoot && AttachedActorRoot->GetAttachParent())
            {
                AttachedActorRoot->DetachFromComponent(FDetachmentTransformRules::KeepWorldTransform);
            }
        }

        if (USceneComponent* OldRootComponent = OldActor->GetRootComponent())
        {
            if (OldRootComponent->GetAttachParent() != nullptr)
            {
                // detach it to remove any scaling
                OldRootComponent->DetachFromComponent(FDetachmentTransformRules::KeepWorldTransform);
            }

            // Save off transform
            TargetWorldTransform = OldRootComponent->GetComponentTransform();
            TargetWorldTransform.SetTranslation(OldRootComponent->GetComponentLocation());  // take into account any custom location
        }

        for (UActorComponent* OldActorComponent: OldActor->GetComponents())
        {
            if (OldActorComponent)
            {
                OldActorComponentNameMap.Add(OldActorComponent->GetFName(), OldActorComponent);
            }
        }
    }

    /**
     * Runs construction scripts on the new actor and then finishes it off by
     * attaching it to the same attachments that its predecessor was set with.
     */
    void Finalize(const TMap<UObject*, UObject*>& OldToNewInstanceMap, TSet<UObject*>* ObjectsThatShouldUseOldStuff, const TArray<UObject*>& ObjectsToReplace, const TMap<FSoftObjectPath, UObject*>& ReinstancedObjectsWeakReferenceMap);

    /**
     * Takes the cached child actors, as well as the old AttachParent, and sets
     * up the new actor so that its attachment hierarchy reflects the old actor
     * that it is replacing. Must be called after *all* instances have been Finalized.
     *
     * @param OldToNewInstanceMap Mapping of reinstanced objects.
     */
    void ApplyAttachments(const TMap<UObject*, UObject*>& OldToNewInstanceMap, TSet<UObject*>* ObjectsThatShouldUseOldStuff, const TArray<UObject*>& ObjectsToReplace, const TMap<FSoftObjectPath, UObject*>& ReinstancedObjectsWeakReferenceMap);

private:
    /**
     * Takes the cached child actors, and attaches them under the new actor.
     *
     * @param  RootComponent	The new actor's root, which the child actors should attach to.
     * @param  OldToNewInstanceMap	Mapping of reinstanced objects. Used for when child and parent actor are of the same type (and thus parent may have been reinstanced, so we can't reattach to the old instance).
     */
    void AttachChildActors(USceneComponent* RootComponent, const TMap<UObject*, UObject*>& OldToNewInstanceMap);

    AActor* NewActor;
    FTransform TargetWorldTransform;
    FActorAttachmentData AttachmentData;
    bool bSelectNewActor;

    /** Holds actor component data, etc. that we use to apply */
    TSharedPtr<AActor::FActorTransactionAnnotation> CachedActorData;

    TMap<FName, UActorComponent*> OldActorComponentNameMap;
};

void FActorReplacementHelper::Finalize(const TMap<UObject*, UObject*>& OldToNewInstanceMap, TSet<UObject*>* ObjectsThatShouldUseOldStuff, const TArray<UObject*>& ObjectsToReplace, const TMap<FSoftObjectPath, UObject*>& ReinstancedObjectsWeakReferenceMap)
{
    if (NewActor->IsPendingKill())
    {
        return;
    }

    // because this is an editor context it's important to use this execution guard
    FEditorScriptExecutionGuard ScriptGuard;

    // run the construction script, which will use the properties we just copied over
    bool bCanReRun = UBlueprint::IsBlueprintHierarchyErrorFree(NewActor->GetClass());
    if (NewActor->CurrentTransactionAnnotation.IsValid() && bCanReRun)
    {
        NewActor->CurrentTransactionAnnotation->ComponentInstanceData.FindAndReplaceInstances(OldToNewInstanceMap);
        NewActor->RerunConstructionScripts();
    }
    else if (CachedActorData.IsValid())
    {
        CachedActorData->ComponentInstanceData.FindAndReplaceInstances(OldToNewInstanceMap);
        const bool bErrorFree = NewActor->ExecuteConstruction(TargetWorldTransform, nullptr, &CachedActorData->ComponentInstanceData);
        if (!bErrorFree)
        {
            // Save off the cached actor data for once the blueprint has been fixed so we can reapply it
            NewActor->CurrentTransactionAnnotation = CachedActorData;
        }
    }
    else
    {
        FComponentInstanceDataCache DummyComponentData;
        NewActor->ExecuteConstruction(TargetWorldTransform, nullptr, &DummyComponentData);
    }

    // The reinstancing case doesn't ever explicitly call Actor->FinishSpawning, we've handled the construction script
    // portion above but still need the PostActorConstruction() case so BeginPlay gets routed correctly while in a BegunPlay world
    if (UWorld* World = NewActor->GetWorld())
    {
        if (World->HasBegunPlay())
        {
            NewActor->PostActorConstruction();
        }
    }

    // make sure that the actor is properly hidden if it's in a hidden sublevel:
    bool bIsInHiddenLevel = false;
    if (ULevel* Level = NewActor->GetLevel())
    {
        bIsInHiddenLevel = !Level->bIsVisible;
    }

    if (bIsInHiddenLevel)
    {
        NewActor->bHiddenEdLevel = true;
        NewActor->MarkComponentsRenderStateDirty();
    }

    if (bSelectNewActor && GEditor)
    {
        GEditor->SelectActor(NewActor, /*bInSelected =*/true, /*bNotify =*/true);
    }

    TMap<UObject*, UObject*> ConstructedComponentReplacementMap;
    for (UActorComponent* NewActorComponent: NewActor->GetComponents())
    {
        if (NewActorComponent)
        {
            if (UActorComponent** OldActorComponent = OldActorComponentNameMap.Find(NewActorComponent->GetFName()))
            {
                ConstructedComponentReplacementMap.Add(*OldActorComponent, NewActorComponent);
            }
        }
    }
    if (GEditor)
    {
        GEditor->NotifyToolsOfObjectReplacement(ConstructedComponentReplacementMap);
    }

    // Destroy actor and clear references.
    NewActor->Modify();
    if (GEditor)
    {
        ULayersSubsystem* Layers = GEditor->GetEditorSubsystem<ULayersSubsystem>();
        if (Layers)
        {
            Layers->InitializeNewActorLayers(NewActor);
        }
    }
}

void FActorReplacementHelper::ApplyAttachments(const TMap<UObject*, UObject*>& OldToNewInstanceMap, TSet<UObject*>* ObjectsThatShouldUseOldStuff, const TArray<UObject*>& ObjectsToReplace, const TMap<FSoftObjectPath, UObject*>& ReinstancedObjectsWeakReferenceMap)
{
    USceneComponent* NewRootComponent = NewActor->GetRootComponent();
    if (NewRootComponent == nullptr)
    {
        return;
    }

    if (AttachmentData.TargetAttachParent)
    {
        UObject* const* NewTargetAttachParent = OldToNewInstanceMap.Find(AttachmentData.TargetAttachParent);
        if (NewTargetAttachParent)
        {
            AttachmentData.TargetAttachParent = CastChecked<AActor>(*NewTargetAttachParent);
        }
    }
    if (AttachmentData.TargetParentComponent)
    {
        UObject* const* NewTargetParentComponent = OldToNewInstanceMap.Find(AttachmentData.TargetParentComponent);
        if (NewTargetParentComponent && *NewTargetParentComponent)
        {
            AttachmentData.TargetParentComponent = CastChecked<USceneComponent>(*NewTargetParentComponent);
        }
    }

    // attach the new instance to original parent
    if (AttachmentData.TargetAttachParent != nullptr)
    {
        if (AttachmentData.TargetParentComponent == nullptr)
        {
            AttachmentData.TargetParentComponent = AttachmentData.TargetAttachParent->GetRootComponent();
        }
        else if (!AttachmentData.TargetParentComponent->IsPendingKill())
        {
            NewRootComponent->AttachToComponent(AttachmentData.TargetParentComponent, FAttachmentTransformRules::KeepWorldTransform, AttachmentData.TargetAttachSocket);
        }
    }

    AttachChildActors(NewRootComponent, OldToNewInstanceMap);
}

void FActorReplacementHelper::AttachChildActors(USceneComponent* RootComponent, const TMap<UObject*, UObject*>& OldToNewInstanceMap)
{
    // if we had attached children reattach them now - unless they are already attached
    for (FAttachedActorInfo& Info: AttachmentData.PendingChildAttachments)
    {
        // Check for a reinstanced attachment, and redirect to the new instance if found
        AActor* NewAttachedActor = Cast<AActor>(OldToNewInstanceMap.FindRef(Info.AttachedActor));
        if (NewAttachedActor)
        {
            Info.AttachedActor = NewAttachedActor;
        }

        // If this actor is no longer attached to anything, reattach
        check(Info.AttachedActor);
        if (!Info.AttachedActor->IsPendingKill() && Info.AttachedActor->GetAttachParentActor() == nullptr)
        {
            USceneComponent* ChildRoot = Info.AttachedActor->GetRootComponent();
            if (ChildRoot && ChildRoot->GetAttachParent() != RootComponent)
            {
                ChildRoot->AttachToComponent(RootComponent, FAttachmentTransformRules::KeepWorldTransform, Info.AttachedToSocket);
                ChildRoot->UpdateComponentToWorld();
            }
        }
    }
}

//
namespace InstancedPropertyUtils
{
typedef TMap<FName, UObject*> FInstancedPropertyMap;

/**
 * Aids in finding instanced property values that will not be duplicated nor
 * copied in CopyPropertiesForUnRelatedObjects().
 */
class FArchiveInstancedSubObjCollector: public FArchiveUObject
{
public:
    //----------------------------------------------------------------------
    FArchiveInstancedSubObjCollector(UObject* TargetObj, FInstancedPropertyMap& PropertyMapOut, bool bAutoSerialize = true)
        : Target(TargetObj), InstancedPropertyMap(PropertyMapOut)
    {
        ArIsObjectReferenceCollector = true;
        this->SetIsPersistent(false);
        ArIgnoreArchetypeRef = false;

        if (bAutoSerialize)
        {
            RunSerialization();
        }
    }

    //----------------------------------------------------------------------
    FArchive& operator<<(UObject*& Obj)
    {
        if (Obj != nullptr)
        {
            FProperty* SerializingProperty = GetSerializedProperty();
            const bool bHasInstancedValue  = SerializingProperty && SerializingProperty->HasAnyPropertyFlags(CPF_PersistentInstance);

            // default sub-objects are handled by CopyPropertiesForUnrelatedObjects()
            if (bHasInstancedValue && !Obj->IsDefaultSubobject())
            {

                UObject* ObjOuter = Obj->GetOuter();
                bool bIsSubObject = (ObjOuter == Target);
                // @TODO: handle nested sub-objects when we're more clear on
                //        how this'll affect the makeup of the reinstanced object
                // 					while (!bIsSubObject && (ObjOuter != nullptr))
                // 					{
                // 						ObjOuter = ObjOuter->GetOuter();
                // 						bIsSubObject |= (ObjOuter == Target);
                // 					}

                if (bIsSubObject)
                {
                    InstancedPropertyMap.Add(SerializingProperty->GetFName(), Obj);
                }
            }
        }
        return *this;
    }

    //----------------------------------------------------------------------
    void RunSerialization()
    {
        InstancedPropertyMap.Empty();
        if (Target != nullptr)
        {
            Target->Serialize(*this);
        }
    }

private:
    UObject* Target;
    FInstancedPropertyMap& InstancedPropertyMap;
};

/**
 * Duplicates and assigns instanced property values that may have been
 * missed by CopyPropertiesForUnRelatedObjects().
 */
class FArchiveInsertInstancedSubObjects: public FArchiveUObject
{
public:
    //----------------------------------------------------------------------
    FArchiveInsertInstancedSubObjects(UObject* TargetObj, const FInstancedPropertyMap& OldInstancedSubObjs, bool bAutoSerialize = true)
        : TargetCDO(TargetObj->GetClass()->GetDefaultObject()), Target(TargetObj), OldInstancedSubObjects(OldInstancedSubObjs)
    {
        ArIsObjectReferenceCollector         = true;
        ArIsModifyingWeakAndStrongReferences = true;

        if (bAutoSerialize)
        {
            RunSerialization();
        }
    }

    //----------------------------------------------------------------------
    FArchive& operator<<(UObject*& Obj)
    {
        if (Obj == nullptr)
        {
            if (FProperty* SerializingProperty = GetSerializedProperty())
            {
                if (UObject* const* OldInstancedObjPtr = OldInstancedSubObjects.Find(SerializingProperty->GetFName()))
                {
                    const UObject* OldInstancedObj = *OldInstancedObjPtr;
                    check(SerializingProperty->HasAnyPropertyFlags(CPF_PersistentInstance));

                    UClass* TargetClass = TargetCDO->GetClass();
                    // @TODO: Handle nested instances when we have more time to flush this all out
                    if (TargetClass->IsChildOf(SerializingProperty->GetOwnerClass()))
                    {
                        FObjectPropertyBase* SerializingObjProperty = CastFieldChecked<FObjectPropertyBase>(SerializingProperty);
                        // being extra careful, not to create our own instanced version when we expect one from the CDO
                        if (SerializingObjProperty->GetObjectPropertyValue_InContainer(TargetCDO) == nullptr)
                        {
                            // @TODO: What if the instanced object is of the same type
                            //        that we're currently reinstancing
                            Obj = StaticDuplicateObject(OldInstancedObj, Target);  // NewObject<UObject>(Target, OldInstancedObj->GetClass()->GetAuthoritativeClass(), OldInstancedObj->GetFName());
                        }
                    }
                }
            }
        }
        return *this;
    }

    //----------------------------------------------------------------------
    void RunSerialization()
    {
        if ((Target != nullptr) && (OldInstancedSubObjects.Num() != 0))
        {
            Target->Serialize(*this);
        }
    }

private:
    UObject* TargetCDO;
    UObject* Target;
    const FInstancedPropertyMap& OldInstancedSubObjects;
};
}  // namespace InstancedPropertyUtils

void FBlueprintCompileReinstancer::ReplaceInstancesOfClass(UClass* OldClass, UClass* NewClass, UObject* OriginalCDO, TSet<UObject*>* ObjectsThatShouldUseOldStuff, bool bClassObjectReplaced, bool bPreserveRootComponent)
{
    TMap<UClass*, UClass*> OldToNewClassMap;
    OldToNewClassMap.Add(OldClass, NewClass);
    ReplaceInstancesOfClass_Inner(OldToNewClassMap, OriginalCDO, ObjectsThatShouldUseOldStuff, bClassObjectReplaced, bPreserveRootComponent);
}

void FBlueprintCompileReinstancer::ReplaceInstancesOfClassEx(const FReplaceInstancesOfClassParameters& Parameters)
{
    TMap<UClass*, UClass*> OldToNewClassMap;
    OldToNewClassMap.Add(Parameters.OldClass, Parameters.NewClass);
    ReplaceInstancesOfClass_Inner(OldToNewClassMap, Parameters.OriginalCDO, Parameters.ObjectsThatShouldUseOldStuff, Parameters.bClassObjectReplaced, Parameters.bPreserveRootComponent, /*bArchetypesAreUpToDate=*/false, Parameters.InstancesThatShouldUseOldClass);
}

void FBlueprintCompileReinstancer::BatchReplaceInstancesOfClass(TMap<UClass*, UClass*>& InOldToNewClassMap, const FBatchReplaceInstancesOfClassParameters& Options)
{
    if (InOldToNewClassMap.Num() == 0)
    {
        return;
    }

    ReplaceInstancesOfClass_Inner(InOldToNewClassMap, nullptr, Options.ObjectsThatShouldUseOldStuff, false /*bClassObjectReplaced*/, true /*bPreserveRootComponent*/, Options.bArchetypesAreUpToDate, Options.InstancesThatShouldUseOldClass, Options.bReplaceReferencesToOldClasses);
}

bool FBlueprintCompileReinstancer::ReinstancerOrderingFunction(UClass* A, UClass* B)
{
    int32 DepthA  = 0;
    int32 DepthB  = 0;
    UStruct* Iter = A ? A->GetSuperStruct() : nullptr;
    while (Iter)
    {
        ++DepthA;
        Iter = Iter->GetSuperStruct();
    }

    Iter = B ? B->GetSuperStruct() : nullptr;
    while (Iter)
    {
        ++DepthB;
        Iter = Iter->GetSuperStruct();
    }

    if (DepthA == DepthB && A && B)
    {
        return A->GetFName().LexicalLess(B->GetFName());
    }
    return DepthA < DepthB;
}

void FBlueprintCompileReinstancer::GetSortedClassHierarchy(UClass* ClassToSearch, TArray<UClass*>& OutHierarchy, UClass** OutNativeParent)
{
    GetDerivedClasses(ClassToSearch, OutHierarchy);

    UClass* Iter = ClassToSearch;
    while (Iter)
    {
        OutHierarchy.Add(Iter);

        // Store the latest native super struct that we know of
        if (Iter->IsNative() && OutNativeParent && *OutNativeParent == nullptr)
        {
            *OutNativeParent = Iter;
        }

        Iter = Iter->GetSuperClass();
    }

    // Sort the hierarchy to get a deterministic result
    OutHierarchy.Sort([](UClass& A, UClass& B) -> bool
                      {
                          return FBlueprintCompileReinstancer::ReinstancerOrderingFunction(&A, &B);
                      });
}

void FBlueprintCompileReinstancer::MoveDependentSkelToReinst(UClass* OwnerClass, TMap<UClass*, UClass*>& OldToNewMap)
{
    // Gather the whole class hierarchy up the native class so that we can correctly create the REINST class parented to native
    TArray<UClass*> ClassHierarchy;
    UClass* NativeParentClass = nullptr;
    FBlueprintCompileReinstancer::GetSortedClassHierarchy(OwnerClass, ClassHierarchy, &NativeParentClass);
    check(NativeParentClass);

    // Traverse the class Hierarchy, and determine if the given class needs to be REINST and have its parent set to the one we created
    const int32 NewParentIndex = ClassHierarchy.Find(OwnerClass);

    for (int32 i = NewParentIndex; i < ClassHierarchy.Num(); ++i)
    {
        UClass* CurClass = ClassHierarchy[i];
        check(CurClass);
        const int32 PrevStructSize         = CurClass->GetStructureSize();

        GIsDuplicatingClassForReinstancing = true;
        // Create a REINST version of the given class
        UObject* OldCDO            = OwnerClass->ClassDefaultObject;
        const FName ReinstanceName = MakeUniqueObjectName(GetTransientPackage(), OwnerClass->GetClass(), *(FString(TEXT("REINST_")) + *OwnerClass->GetName()));

        checkf(!OwnerClass->IsPendingKill(), TEXT("%s is PendingKill - will not duplicate successfully"), *(OwnerClass->GetName()));
        UClass* ReinstClass = CastChecked<UClass>(StaticDuplicateObject(CurClass, GetTransientPackage(), ReinstanceName, ~RF_Transactional));

        ReinstClass->RemoveFromRoot();
        OwnerClass->ClassFlags &= ~CLASS_NewerVersionExists;
        GIsDuplicatingClassForReinstancing = false;

        UClass** OverridenParent           = OldToNewMap.Find(ReinstClass->GetSuperClass());
        if (OverridenParent && *OverridenParent)
        {
            ReinstClass->SetSuperStruct(*OverridenParent);
        }

        ReinstClass->Bind();
        ReinstClass->StaticLink(true);

        // Map the old class to the new one
        OldToNewMap.Add(CurClass, ReinstClass);

        // Actually move the old CDO reference out of the way
        if (OldCDO)
        {
            OwnerClass->ClassDefaultObject = nullptr;
            OldCDO->Rename(nullptr, ReinstClass->GetOuter(), REN_DoNotDirty | REN_DontCreateRedirectors | REN_ForceNoResetLoaders);
            ReinstClass->ClassDefaultObject = OldCDO;
            OldCDO->SetClass(ReinstClass);
        }

        // Ensure that we are not changing the class layout by setting a new super struct,
        // if they do not match we may see crashes because instances of the structs do match the
        // correct layout size
        const int32 NewStructSize = ReinstClass->GetStructureSize();
        ensure(PrevStructSize == NewStructSize);
    }
}

UClass* FBlueprintCompileReinstancer::MoveCDOToNewClass(UClass* OwnerClass, const TMap<UClass*, UClass*>& OldToNewMap, bool bAvoidCDODuplication)
{
    GIsDuplicatingClassForReinstancing = true;
    OwnerClass->ClassFlags |= CLASS_NewerVersionExists;

    ensureMsgf(!FBlueprintCompileReinstancer::IsReinstClass(OwnerClass), TEXT("OwnerClass should not be 'REINST_'! This means that a REINST class was parented to another REINST class, causing unwanted recursion!"));

    // For consistency I'm moving archetypes that are outered to the UClass aside. The current implementation
    // of IsDefaultSubobject (used by StaticDuplicateObject) will not duplicate these instances if they
    // are based on the CDO, but if they are based on another archetype (ie, they are inherited) then
    // they will be considered sub objects and they will be duplicated. There is no reason to duplicate
    // these archetypes here, so we move them aside and restore them after the uclass has been duplicated:
    TArray<UObject*> OwnedObjects;
    GetObjectsWithOuter(OwnerClass, OwnedObjects, false);
    // record original names:
    TArray<FName> OriginalNames;
    for (UObject* OwnedObject: OwnedObjects)
    {
        OriginalNames.Add(OwnedObject->GetFName());
        if (OwnedObject->HasAnyFlags(RF_ArchetypeObject))
        {
            OwnedObject->Rename(nullptr, GetTransientPackage(), REN_DoNotDirty | REN_DontCreateRedirectors | REN_ForceNoResetLoaders);
        }
    }

    UObject* OldCDO            = OwnerClass->ClassDefaultObject;
    const FName ReinstanceName = MakeUniqueObjectName(GetTransientPackage(), OwnerClass->GetClass(), *(FString(TEXT("REINST_")) + *OwnerClass->GetName()));

    checkf(!OwnerClass->IsPendingKill(), TEXT("%s is PendingKill - will not duplicate successfully"), *(OwnerClass->GetName()));
    UClass* CopyOfOwnerClass = CastChecked<UClass>(StaticDuplicateObject(OwnerClass, GetTransientPackage(), ReinstanceName, ~RF_Transactional));

    CopyOfOwnerClass->RemoveFromRoot();
    OwnerClass->ClassFlags &= ~CLASS_NewerVersionExists;
    GIsDuplicatingClassForReinstancing = false;

    UClass* const* OverridenParent     = OldToNewMap.Find(CopyOfOwnerClass->GetSuperClass());
    if (OverridenParent && *OverridenParent)
    {
        CopyOfOwnerClass->SetSuperStruct(*OverridenParent);
    }

    UBlueprintGeneratedClass* BPClassToReinstance = Cast<UBlueprintGeneratedClass>(OwnerClass);
    UBlueprintGeneratedClass* BPGDuplicatedClass  = Cast<UBlueprintGeneratedClass>(CopyOfOwnerClass);
    if (BPGDuplicatedClass && BPClassToReinstance && BPClassToReinstance->OverridenArchetypeForCDO)
    {
        BPGDuplicatedClass->OverridenArchetypeForCDO = BPClassToReinstance->OverridenArchetypeForCDO;
    }

#if VALIDATE_UBER_GRAPH_PERSISTENT_FRAME
    if (BPGDuplicatedClass && BPClassToReinstance)
    {
        BPGDuplicatedClass->UberGraphFunctionKey = BPClassToReinstance->UberGraphFunctionKey;
    }
#endif

    UFunction* DuplicatedClassUberGraphFunction = BPGDuplicatedClass ? BPGDuplicatedClass->UberGraphFunction : nullptr;
    if (DuplicatedClassUberGraphFunction)
    {
        DuplicatedClassUberGraphFunction->Bind();
        DuplicatedClassUberGraphFunction->StaticLink(true);
    }

    for (int32 I = 0; I < OwnedObjects.Num(); ++I)
    {
        UObject* OwnedArchetype = OwnedObjects[I];
        if (OwnedArchetype->HasAnyFlags(RF_ArchetypeObject))
        {
            OwnedArchetype->Rename(*OriginalNames[I].ToString(), OwnerClass, REN_DoNotDirty | REN_DontCreateRedirectors | REN_ForceNoResetLoaders);
        }
    }

    CopyOfOwnerClass->Bind();
    CopyOfOwnerClass->StaticLink(true);

    if (OldCDO)
    {
        // @todo: #dano, rename bAvoidCDODuplication because it's really a flag to move the CDO aside not 'prevent duplication':
        if (bAvoidCDODuplication)
        {
            OwnerClass->ClassDefaultObject = nullptr;
            OldCDO->Rename(nullptr, CopyOfOwnerClass->GetOuter(), REN_DoNotDirty | REN_DontCreateRedirectors | REN_ForceNoResetLoaders);
            CopyOfOwnerClass->ClassDefaultObject = OldCDO;
        }
        OldCDO->SetClass(CopyOfOwnerClass);
    }
    return CopyOfOwnerClass;
}

bool FBlueprintCompileReinstancer::IsReinstClass(const UClass* Class)
{
    static const FString ReinstPrefix = TEXT("REINST");
    return Class && Class->GetFName().ToString().StartsWith(ReinstPrefix);
}

static void ReplaceObjectHelper(UObject*& OldObject, UClass* OldClass, UObject*& NewUObject, UClass* NewClass, TMap<UObject*, UObject*>& OldToNewInstanceMap, TMap<UObject*, FName>& OldToNewNameMap, int32 OldObjIndex, TArray<UObject*>& ObjectsToReplace, TArray<UObject*>& PotentialEditorsForRefreshing, TSet<AActor*>& OwnersToRerunConstructionScript, TFunctionRef<TArray<USceneComponent*>&(USceneComponent*)> GetAttachChildrenArray, bool bIsComponent, bool bArchetypesAreUpToDate)
{
    const EObjectFlags FlagMask = RF_Public | RF_ArchetypeObject | RF_Transactional | RF_Transient | RF_TextExportTransient | RF_InheritableComponentTemplate | RF_Standalone;  // TODO: what about RF_RootSet?
    // If the old object was spawned from an archetype (i.e. not the CDO), we must use the new version of that archetype as the template object when constructing the new instance.
    UObject* NewArchetype = nullptr;
    if (bArchetypesAreUpToDate)
    {
        FName NewName = OldToNewNameMap.FindRef(OldObject);
        if (NewName == NAME_None)
        {
            // Otherwise, just use the old object's current name.
            NewName = OldObject->GetFName();
        }
        NewArchetype = UObject::GetArchetypeFromRequiredInfo(NewClass, OldObject->GetOuter(), NewName, OldObject->GetFlags() & FlagMask);
    }
    else
    {
        UObject* OldArchetype      = OldObject->GetArchetype();
        NewArchetype               = OldToNewInstanceMap.FindRef(OldArchetype);

        bool bArchetypeReinstanced = (OldArchetype == OldClass->GetDefaultObject()) || (NewArchetype != nullptr);
        // if we don't have a updated archetype to spawn from, we need to update/reinstance it
        while (!bArchetypeReinstanced)
        {
            int32 ArchetypeIndex = ObjectsToReplace.Find(OldArchetype);
            if (ArchetypeIndex != INDEX_NONE)
            {
                if (ensure(ArchetypeIndex > OldObjIndex))
                {
                    // if this object has an archetype, but it hasn't been
                    // reinstanced yet (but is queued to) then we need to swap out
                    // the two, and reinstance the archetype first
                    ObjectsToReplace.Swap(ArchetypeIndex, OldObjIndex);
                    OldObject = ObjectsToReplace[OldObjIndex];
                    check(OldObject == OldArchetype);

                    OldArchetype          = OldObject->GetArchetype();
                    NewArchetype          = OldToNewInstanceMap.FindRef(OldArchetype);
                    bArchetypeReinstanced = (OldArchetype == OldClass->GetDefaultObject()) || (NewArchetype != nullptr);
                }
                else
                {
                    break;
                }
            }
            else
            {
                break;
            }
        }
        // Check that either this was an instance of the class directly, or we found a new archetype for it
        ensureMsgf(bArchetypeReinstanced, TEXT("Reinstancing non-actor (%s); failed to resolve archetype object - property values may be lost."), *OldObject->GetPathName());
    }

    EObjectFlags OldFlags = OldObject->GetFlags();

    FName OldName(OldObject->GetFName());

    // If the old object is in this table, we've already renamed it away in a previous iteration. Don't rename it again!
    if (!OldToNewNameMap.Contains(OldObject))
    {
        // If we're reinstancing a component template, we also need to rename any inherited templates that are found to be based on it, in order to preserve archetype paths.
        if (bIsComponent && OldObject->HasAllFlags(RF_ArchetypeObject) && OldObject->GetOuter()->IsA<UBlueprintGeneratedClass>())
        {
            // Gather all component templates from the current archetype to the farthest antecedent inherited template(s).
            TArray<UObject*> OldArchetypeObjects;
            FArchetypeReinstanceHelper::GetArchetypeObjects(OldObject, OldArchetypeObjects, RF_InheritableComponentTemplate);

            // Find a unique object name that does not conflict with anything in the scope of all outers in the template chain.
            const FString OldArchetypeName = FArchetypeReinstanceHelper::FindUniqueArchetypeObjectName(OldArchetypeObjects).ToString();

            for (UObject* OldArchetypeObject: OldArchetypeObjects)
            {
                OldToNewNameMap.Add(OldArchetypeObject, OldName);
                OldArchetypeObject->Rename(*OldArchetypeName, OldArchetypeObject->GetOuter(), REN_DoNotDirty | REN_DontCreateRedirectors | REN_ForceNoResetLoaders);
            }
        }
        else
        {
            OldObject->Rename(nullptr, OldObject->GetOuter(), REN_DoNotDirty | REN_DontCreateRedirectors | REN_ForceNoResetLoaders);
        }
    }

    {
        // We may have already renamed this object to temp space if it was an inherited archetype in a previous iteration; check for that here.
        FName NewName = OldToNewNameMap.FindRef(OldObject);
        if (NewName == NAME_None)
        {
            // Otherwise, just use the old object's current name.
            NewName = OldName;
        }

        FMakeClassSpawnableOnScope TemporarilySpawnable(NewClass);
        NewUObject = NewObject<UObject>(OldObject->GetOuter(), NewClass, NewName, RF_NoFlags, NewArchetype);
    }

    check(NewUObject != nullptr);

    NewUObject->SetFlags(OldFlags & FlagMask);

    InstancedPropertyUtils::FInstancedPropertyMap InstancedPropertyMap;
    InstancedPropertyUtils::FArchiveInstancedSubObjCollector InstancedSubObjCollector(OldObject, InstancedPropertyMap);
    UEngine::FCopyPropertiesForUnrelatedObjectsParams Options;
    Options.bNotifyObjectReplacement = true;
    UEditorEngine::CopyPropertiesForUnrelatedObjects(OldObject, NewUObject, Options);
    InstancedPropertyUtils::FArchiveInsertInstancedSubObjects InstancedSubObjSpawner(NewUObject, InstancedPropertyMap);

    UWorld* RegisteredWorld = nullptr;
    bool bWasRegistered     = false;
    if (bIsComponent)
    {
        UActorComponent* OldComponent = CastChecked<UActorComponent>(OldObject);
        if (OldComponent->IsRegistered())
        {
            bWasRegistered  = true;
            RegisteredWorld = OldComponent->GetWorld();
            OldComponent->UnregisterComponent();
        }
    }

    OldObject->RemoveFromRoot();
    OldObject->MarkPendingKill();

    OldToNewInstanceMap.Add(OldObject, NewUObject);

    if (bIsComponent)
    {
        UActorComponent* Component = CastChecked<UActorComponent>(NewUObject);
        AActor* OwningActor        = Component->GetOwner();
        if (OwningActor)
        {
            OwningActor->ResetOwnedComponents();

            // Check to see if they have an editor that potentially needs to be refreshed
            if (OwningActor->GetClass()->ClassGeneratedBy)
            {
                PotentialEditorsForRefreshing.AddUnique(OwningActor->GetClass()->ClassGeneratedBy);
            }

            // we need to keep track of actor instances that need
            // their construction scripts re-ran (since we've just
            // replaced a component they own)
            OwnersToRerunConstructionScript.Add(OwningActor);
        }

        if (bWasRegistered)
        {
            if (RegisteredWorld && OwningActor == nullptr)
            {
                // Thumbnail components are added to a World without an actor, so we must special case their
                // REINST to register them with the world again.
                // The old thumbnail component is GC'd and will ensure if all it's attachments are not released
                // @TODO: This special case can breakdown if the nature of thumbnail components changes and could
                // use a cleanup later.
                if (OldObject->GetOutermost() == GetTransientPackage())
                {
                    if (USceneComponent* SceneComponent = Cast<USceneComponent>(OldObject))
                    {
                        GetAttachChildrenArray(SceneComponent).Empty();
                        SceneComponent->SetupAttachment(nullptr);
                    }
                }

                Component->RegisterComponentWithWorld(RegisteredWorld);
            }
            else
            {
                Component->RegisterComponent();
            }
        }
    }
}

static void ReplaceActorHelper(AActor* OldActor, UClass* OldClass, UObject*& NewUObject, UClass* NewClass, TMap<UObject*, UObject*>& OldToNewInstanceMap, TMap<UClass*, UClass*>& InOldToNewClassMap, TMap<FSoftObjectPath, UObject*>& ReinstancedObjectsWeakReferenceMap, TMap<UObject*, FActorAttachmentData>& ActorAttachmentData, TArray<FActorReplacementHelper>& ReplacementActors, bool bPreserveRootComponent, bool& bSelectionChanged)
{
    FVector Location  = FVector::ZeroVector;
    FRotator Rotation = FRotator::ZeroRotator;
    if (USceneComponent* OldRootComponent = OldActor->GetRootComponent())
    {
        // We need to make sure that the GetComponentTransform() transform is up to date, but we don't want to run any initialization logic
        // so we silence the update, cache it off, revert the change (so no events are raised), and then directly update the transform
        // with the value calculated in ConditionalUpdateComponentToWorld:
        FScopedMovementUpdate SilenceMovement(OldRootComponent);

        OldRootComponent->ConditionalUpdateComponentToWorld();
        FTransform OldComponentToWorld = OldRootComponent->GetComponentTransform();
        SilenceMovement.RevertMove();

        OldRootComponent->SetComponentToWorld(OldComponentToWorld);
        Location = OldActor->GetActorLocation();
        Rotation = OldActor->GetActorRotation();
    }

    // If this actor was spawned from an Archetype, we spawn the new actor from the new version of that archetype
    UObject* OldArchetype = OldActor->GetArchetype();
    UWorld* World         = OldActor->GetWorld();
    AActor* NewArchetype  = Cast<AActor>(OldToNewInstanceMap.FindRef(OldArchetype));
    // Check that either this was an instance of the class directly, or we found a new archetype for it
    check(OldArchetype == OldClass->GetDefaultObject() || NewArchetype);

    // Spawn the new actor instance, in the same level as the original, but deferring running the construction script until we have transferred modified properties
    ULevel* ActorLevel   = OldActor->GetLevel();
    UClass** MappedClass = InOldToNewClassMap.Find(OldActor->GetClass());
    UClass* SpawnClass   = MappedClass ? *MappedClass : NewClass;

    FActorSpawnParameters SpawnInfo;
    SpawnInfo.OverrideLevel                  = ActorLevel;
    SpawnInfo.Owner                          = OldActor->GetOwner();
    SpawnInfo.Instigator                     = OldActor->GetInstigator();
    SpawnInfo.Template                       = NewArchetype;
    SpawnInfo.SpawnCollisionHandlingOverride = ESpawnActorCollisionHandlingMethod::AlwaysSpawn;
    SpawnInfo.bDeferConstruction             = true;
    SpawnInfo.Name                           = OldActor->GetFName();

    if (!OldActor->IsListedInSceneOutliner())
    {
        SpawnInfo.bHideFromSceneOutliner = true;
    }

    SpawnInfo.OverridePackage   = OldActor->GetExternalPackage();
    SpawnInfo.OverrideActorGuid = OldActor->GetActorGuid();

    OldActor->Rename(nullptr, OldActor->GetOuter(), REN_DoNotDirty | REN_DontCreateRedirectors | REN_ForceNoResetLoaders);

    AActor* NewActor = nullptr;
    {
        FMakeClassSpawnableOnScope TemporarilySpawnable(SpawnClass);
        NewActor = World->SpawnActor(SpawnClass, &Location, &Rotation, SpawnInfo);
    }

    if (OldActor->CurrentTransactionAnnotation.IsValid())
    {
        NewActor->CurrentTransactionAnnotation = OldActor->CurrentTransactionAnnotation;
    }

    check(NewActor != nullptr);
    NewUObject = NewActor;
    // store the new actor for the second pass (NOTE: this detaches
    // OldActor from all child/parent attachments)
    //
    // running the NewActor's construction-script is saved for that
    // second pass (because the construction-script may reference
    // another instance that hasn't been replaced yet).
    FActorAttachmentData& CurrentAttachmentData = ActorAttachmentData.FindChecked(OldActor);
    ReplacementActors.Add(FActorReplacementHelper(NewActor, OldActor, MoveTemp(CurrentAttachmentData)));
    ActorAttachmentData.Remove(OldActor);

    ReinstancedObjectsWeakReferenceMap.Add(OldActor, NewUObject);

    OldActor->DestroyConstructedComponents();  // don't want to serialize components from the old actor
                                               // Unregister native components so we don't copy any sub-components they generate for themselves (like UCameraComponent does)
    OldActor->UnregisterAllComponents();

    // Unregister any native components, might have cached state based on properties we are going to overwrite
    NewActor->UnregisterAllComponents();

    UEngine::FCopyPropertiesForUnrelatedObjectsParams Params;
    Params.bPreserveRootComponent                 = bPreserveRootComponent;
    Params.bAggressiveDefaultSubobjectReplacement = true;
    Params.bNotifyObjectReplacement               = true;
    UEngine::CopyPropertiesForUnrelatedObjects(OldActor, NewActor, Params);

    // reset properties/streams
    NewActor->ResetPropertiesForConstruction();
    // register native components
    NewActor->RegisterAllComponents();

    //
    // clean up the old actor (unselect it, remove it from the world, etc.)...

    if (OldActor->IsSelected())
    {
        if (GEditor)
        {
            GEditor->SelectActor(OldActor, /*bInSelected =*/false, /*bNotify =*/false);
        }
        bSelectionChanged = true;
    }
    if (GEditor)
    {
        ULayersSubsystem* Layers = GEditor->GetEditorSubsystem<ULayersSubsystem>();
        if (Layers)
        {
            Layers->DisassociateActorFromLayers(OldActor);
        }
    }

    OldToNewInstanceMap.Add(OldActor, NewActor);
}

void FBlueprintCompileReinstancer::ReplaceInstancesOfClass_Inner(TMap<UClass*, UClass*>& InOldToNewClassMap, UObject* InOriginalCDO, TSet<UObject*>* ObjectsThatShouldUseOldStuff, bool bClassObjectReplaced, bool bPreserveRootComponent, bool bArchetypesAreUpToDate, const TSet<UObject*>* InstancesThatShouldUseOldClass, bool bReplaceReferencesToOldClasses)
{
    // If there is an original CDO, we are only reinstancing a single class
    check((InOriginalCDO != nullptr && InOldToNewClassMap.Num() == 1) || InOriginalCDO == nullptr);  // (InOldToNewClassMap.Num() > 1 && InOriginalCDO == nullptr) || (InOldToNewClassMap.Num() == 1 && InOriginalCDO != nullptr));

    if (InOldToNewClassMap.Num() == 0)
    {
        return;
    }

    USelection* SelectedActors = nullptr;
    TArray<UObject*> ObjectsReplaced;
    bool bSelectionChanged     = false;
    bool bFixupSCS             = false;
    const bool bLogConversions = false;  // for debugging

    // Map of old objects to new objects
    TMap<UObject*, UObject*> OldToNewInstanceMap;

    // Map of old objects to new name (used to assist with reinstancing archetypes)
    TMap<UObject*, FName> OldToNewNameMap;

    TMap<FSoftObjectPath, UObject*> ReinstancedObjectsWeakReferenceMap;

    // actors being replace
    TArray<FActorReplacementHelper> ReplacementActors;

    // A list of objects (e.g. Blueprints) that potentially have editors open that we need to refresh
    TArray<UObject*> PotentialEditorsForRefreshing;

    // A list of component owners that need their construction scripts re-ran (because a component of theirs has been reinstanced)
    TSet<AActor*> OwnersToRerunConstructionScript;

    // Set global flag to let system know we are reconstructing blueprint instances
    TGuardValue<bool> GuardTemplateNameFlag(GIsReconstructingBlueprintInstances, true);

    struct FObjectRemappingHelper
    {
        void OnObjectsReplaced(const TMap<UObject*, UObject*>& InReplacedObjects)
        {
            for (const TPair<UObject*, UObject*>& Pair: InReplacedObjects)
            {
                // CPFUO is going to tell us that the old class
                // has been replaced with the new class, but we created
                // the old class and we don't want to blindly replace
                // references to the old class. This could cause, for example,
                // the compilation manager to replace its references to the
                // old class with references to the new class:
                if (Pair.Key == nullptr ||
                    Pair.Value == nullptr ||
                    (!Pair.Key->IsA<UClass>() &&
                     !Pair.Value->IsA<UClass>()))
                {
                    ReplacedObjects.Add(Pair);
                }
            }
        }

        TMap<UObject*, UObject*> ReplacedObjects;
    } ObjectRemappingHelper;

    FDelegateHandle OnObjectsReplacedHandle = FDelegateHandle();
    if (GEditor)
    {
        OnObjectsReplacedHandle = GEditor->OnObjectsReplaced().AddRaw(&ObjectRemappingHelper, &FObjectRemappingHelper::OnObjectsReplaced);
    }

    auto UpdateObjectBeingDebugged = [](UObject* InOldObject, UObject* InNewObject)
    {
        if (UBlueprint* OldObjBlueprint = Cast<UBlueprint>(InOldObject->GetClass()->ClassGeneratedBy))
        {
            // For now, don't update the object if the outer BP assets don't match (e.g. after a reload). Otherwise, it will
            // trigger an ensure() in SetObjectBeginDebugged(). This will be replaced with a better solution in a future release.
            if (OldObjBlueprint == Cast<UBlueprint>(InNewObject->GetClass()->ClassGeneratedBy))
            {
                // The old object may already be PendingKill, but we still want to check the current
                // ptr value for a match. Otherwise, the selection will get cleared after every compile.
                const UObject* DebugObj = OldObjBlueprint->GetObjectBeingDebugged(EGetObjectOrWorldBeingDebuggedFlags::IgnorePendingKill);
                if (DebugObj == InOldObject)
                {
                    OldObjBlueprint->SetObjectBeingDebugged(InNewObject);
                }
            }
        }
    };

    {
        TArray<UObject*> ObjectsToReplace;

        BP_SCOPED_COMPILER_EVENT_STAT(EKismetReinstancerStats_ReplaceInstancesOfClass);
        if (GEditor && GEditor->GetSelectedActors())
        {
            SelectedActors = GEditor->GetSelectedActors();
            SelectedActors->BeginBatchSelectOperation();
            SelectedActors->Modify();
        }

        // WARNING: for (TPair<UClass*, UClass*> OldToNewClass : InOldToNewClassMap) duplicated below
        // to handle reconstructing actors which need to be reinstanced after their owned components
        // have been updated:
        for (TPair<UClass*, UClass*> OldToNewClass: InOldToNewClassMap)
        {
            UClass* OldClass = OldToNewClass.Key;
            UClass* NewClass = OldToNewClass.Value;
            check(OldClass && NewClass);
#if WITH_HOT_RELOAD
            check(OldClass != NewClass || GIsHotReload);
#else
            check(OldClass != NewClass);
#endif
            {
                const bool bIsComponent = NewClass->IsChildOf<UActorComponent>();

                // If any of the class changes are of an actor component to scene component or reverse then we will fixup SCS of all actors affected
                if (bIsComponent && !bFixupSCS)
                {
                    bFixupSCS = (NewClass->IsChildOf<USceneComponent>() != OldClass->IsChildOf<USceneComponent>());
                }

                const bool bIncludeDerivedClasses = false;
                ObjectsToReplace.Reset();
                GetObjectsOfClass(OldClass, ObjectsToReplace, bIncludeDerivedClasses);
                // Then fix 'real' (non archetype) instances of the class
                for (int32 OldObjIndex = 0; OldObjIndex < ObjectsToReplace.Num(); ++OldObjIndex)
                {
                    UObject* OldObject = ObjectsToReplace[OldObjIndex];

                    AActor* OldActor   = Cast<AActor>(OldObject);

                    // Skip archetype instances, EXCEPT for component templates and child actor templates
                    const bool bIsChildActorTemplate = OldActor && OldActor->GetOuter()->IsA<UChildActorComponent>();
                    if (OldObject->IsPendingKill() ||
                        (!bIsComponent && !bIsChildActorTemplate && OldObject->IsTemplate()) ||
                        (InstancesThatShouldUseOldClass && InstancesThatShouldUseOldClass->Contains(OldObject)))
                    {
                        continue;
                    }

                    // WARNING: This loop only handles non-actor objects, actor objects are handled below:
                    if (OldActor == nullptr)
                    {
                        UObject* NewUObject = nullptr;
                        ReplaceObjectHelper(OldObject, OldClass, NewUObject, NewClass, OldToNewInstanceMap, OldToNewNameMap, OldObjIndex, ObjectsToReplace, PotentialEditorsForRefreshing, OwnersToRerunConstructionScript, &FDirectAttachChildrenAccessor::Get, bIsComponent, bArchetypesAreUpToDate);
                        UpdateObjectBeingDebugged(OldObject, NewUObject);
                        ObjectsReplaced.Add(OldObject);

                        if (bLogConversions)
                        {
                            UE_LOG(LogBlueprint, Log, TEXT("Converted instance '%s' to '%s'"), *GetPathNameSafe(OldObject), *GetPathNameSafe(NewUObject));
                        }
                    }
                }
            }
        }

        FDelegateHandle OnLevelActorDeletedHandle = GEngine ? GEngine->OnLevelActorDeleted().AddLambda([&OldToNewInstanceMap](AActor* DestroyedActor)
                                                                                                       {
                                                                                                           if (UObject** ReplacementObject = OldToNewInstanceMap.Find(DestroyedActor))
                                                                                                           {
                                                                                                               AActor* ReplacementActor = CastChecked<AActor>(*ReplacementObject);
                                                                                                               ReplacementActor->GetWorld()->EditorDestroyActor(ReplacementActor, /*bShouldModifyLevel =*/true);
                                                                                                           }
                                                                                                       }) :
                                                              FDelegateHandle();

        // WARNING: for (TPair<UClass*, UClass*> OldToNewClass : InOldToNewClassMap) duplicated above
        // this loop only handles actors - which need to be reconstructed *after* their owned components
        // have been reinstanced:
        for (TPair<UClass*, UClass*> OldToNewClass: InOldToNewClassMap)
        {
            UClass* OldClass = OldToNewClass.Key;
            UClass* NewClass = OldToNewClass.Value;
            check(OldClass && NewClass);

            {
                const bool bIncludeDerivedClasses = false;
                ObjectsToReplace.Reset();
                GetObjectsOfClass(OldClass, ObjectsToReplace, bIncludeDerivedClasses);

                // store old attachment data before we mess with components, etc:
                TMap<UObject*, FActorAttachmentData> ActorAttachmentData;
                for (int32 OldObjIndex = 0; OldObjIndex < ObjectsToReplace.Num(); ++OldObjIndex)
                {
                    UObject* OldObject = ObjectsToReplace[OldObjIndex];
                    if (OldObject->IsPendingKill() ||
                        (InstancesThatShouldUseOldClass && InstancesThatShouldUseOldClass->Contains(OldObject)))
                    {
                        continue;
                    }

                    if (AActor* OldActor = Cast<AActor>(OldObject))
                    {
                        ActorAttachmentData.Add(OldObject, FActorAttachmentData(OldActor));
                    }
                }

                // Then fix 'real' (non archetype) instances of the class
                for (int32 OldObjIndex = 0; OldObjIndex < ObjectsToReplace.Num(); ++OldObjIndex)
                {
                    UObject* OldObject = ObjectsToReplace[OldObjIndex];
                    AActor* OldActor   = Cast<AActor>(OldObject);

                    // Skip archetype instances, EXCEPT for child actor templates
                    const bool bIsChildActorTemplate = OldActor && OldActor->GetOuter()->IsA<UChildActorComponent>();
                    if (OldObject->IsPendingKill() ||
                        (!bIsChildActorTemplate && OldObject->IsTemplate()) ||
                        (InstancesThatShouldUseOldClass && InstancesThatShouldUseOldClass->Contains(OldObject)))
                    {
                        continue;
                    }

                    // WARNING: This loop only handles actor objects that are in a level, all other objects are
                    // handled above
                    if (OldActor != nullptr)
                    {
                        UObject* NewUObject = nullptr;
                        if (OldActor->GetLevel())
                        {
                            ReplaceActorHelper(OldActor, OldClass, NewUObject, NewClass, OldToNewInstanceMap, InOldToNewClassMap, ReinstancedObjectsWeakReferenceMap, ActorAttachmentData, ReplacementActors, bPreserveRootComponent, bSelectionChanged);
                        }
                        else
                        {
                            // Actors that are not in a level cannot be reconstructed, sequencer team decided to reinstance these as normal objects:
                            ReplaceObjectHelper(OldObject, OldClass, NewUObject, NewClass, OldToNewInstanceMap, OldToNewNameMap, OldObjIndex, ObjectsToReplace, PotentialEditorsForRefreshing, OwnersToRerunConstructionScript, &FDirectAttachChildrenAccessor::Get, false, bArchetypesAreUpToDate);
                        }
                        UpdateObjectBeingDebugged(OldObject, NewUObject);
                        ObjectsReplaced.Add(OldObject);

                        if (bLogConversions)
                        {
                            UE_LOG(LogBlueprint, Log, TEXT("Converted instance '%s' to '%s'"), *GetPathNameSafe(OldObject), *GetPathNameSafe(NewUObject));
                        }
                    }
                }
            }
        }
        if (GEngine)
        {
            GEngine->OnLevelActorDeleted().Remove(OnLevelActorDeletedHandle);
        }

        for (TPair<UObject*, UObject*> ReinstancedPair: OldToNewInstanceMap)
        {
            if (AActor* OldActor = Cast<AActor>(ReinstancedPair.Key))
            {
                if (UWorld* World = OldActor->GetWorld())
                {
                    World->EditorDestroyActor(OldActor, /*bShouldModifyLevel =*/true);
                }
            }
        }
    }

    if (GEditor)
    {
        GEditor->OnObjectsReplaced().Remove(OnObjectsReplacedHandle);
    }

    // Now replace any pointers to the old archetypes/instances with pointers to the new one
    TArray<UObject*> SourceObjects;
    OldToNewInstanceMap.GenerateKeyArray(SourceObjects);

    if (InOriginalCDO)
    {
        check(InOldToNewClassMap.Num() == 1);
        for (TPair<UClass*, UClass*> OldToNewClass: InOldToNewClassMap)
        {
            UClass* OldClass = OldToNewClass.Key;
            UClass* NewClass = OldToNewClass.Value;
            check(OldClass && NewClass);
#if WITH_HOT_RELOAD
            check(OldClass != NewClass || GIsHotReload);
#else
            check(OldClass != NewClass);
#endif

            FReplaceReferenceHelper::IncludeCDO(OldClass, NewClass, OldToNewInstanceMap, SourceObjects, InOriginalCDO);

            if (bClassObjectReplaced)
            {
                FReplaceReferenceHelper::IncludeClass(OldClass, NewClass, OldToNewInstanceMap, SourceObjects, ObjectsReplaced);
            }
        }
    }

    {
        BP_SCOPED_COMPILER_EVENT_STAT(EKismetReinstancerStats_ReplacementConstruction);

        // the process of setting up new replacement actors is split into two
        // steps (this here, is the second)...
        //
        // the "finalization" here runs the replacement actor's construction-
        // script and is left until late to account for a scenario where the
        // construction-script attempts to modify another instance of the
        // same class... if this were to happen above, in the ObjectsToReplace
        // loop, then accessing that other instance would cause an assert in
        // FProperty::ContainerPtrToValuePtrInternal() (which appropriatly
        // complains that the other instance's type doesn't match because it
        // hasn't been replaced yet... that's why we wait until after
        // FArchiveReplaceObjectRef to run construction-scripts).
        for (FActorReplacementHelper& ReplacementActor: ReplacementActors)
        {
            ReplacementActor.Finalize(ObjectRemappingHelper.ReplacedObjects, ObjectsThatShouldUseOldStuff, ObjectsReplaced, ReinstancedObjectsWeakReferenceMap);
        }

        for (FActorReplacementHelper& ReplacementActor: ReplacementActors)
        {
            ReplacementActor.ApplyAttachments(ObjectRemappingHelper.ReplacedObjects, ObjectsThatShouldUseOldStuff, ObjectsReplaced, ReinstancedObjectsWeakReferenceMap);
        }

        OldToNewInstanceMap.Append(ObjectRemappingHelper.ReplacedObjects);
    }

    if (bReplaceReferencesToOldClasses)
    {
        check(ObjectsThatShouldUseOldStuff);

        for (TPair<UClass*, UClass*> OldToNew: InOldToNewClassMap)
        {
            ObjectsThatShouldUseOldStuff->Add(OldToNew.Key);

            TArray<UObject*> OldFunctions;
            GetObjectsWithOuter(OldToNew.Key, OldFunctions);
            ObjectsThatShouldUseOldStuff->Append(OldFunctions);

            OldToNewInstanceMap.Add(OldToNew.Key, OldToNew.Value);
            SourceObjects.Add(OldToNew.Key);
        }
    }

    FReplaceReferenceHelper::FindAndReplaceReferences(SourceObjects, ObjectsThatShouldUseOldStuff, ObjectsReplaced, OldToNewInstanceMap, ReinstancedObjectsWeakReferenceMap);

    for (UObject* Obj: ObjectsReplaced)
    {
        UObject** NewObject = OldToNewInstanceMap.Find(Obj);
        if (NewObject && *NewObject)
        {
            if (UAnimInstance* AnimTree = Cast<UAnimInstance>(*NewObject))
            {
                // Initialising the anim instance isn't enough to correctly set up the skeletal mesh again in a
                // paused world, need to initialise the skeletal mesh component that contains the anim instance.
                if (USkeletalMeshComponent* SkelComponent = Cast<USkeletalMeshComponent>(AnimTree->GetOuter()))
                {
                    SkelComponent->ClearAnimScriptInstance();
                    SkelComponent->InitAnim(true);
                    // compile change ignores motion vector, so ignore this.
                    SkelComponent->ClearMotionVector();
                }
            }
        }
    }

    if (SelectedActors)
    {
        SelectedActors->EndBatchSelectOperation();
    }

    if (bSelectionChanged && GEditor)
    {
        GEditor->NoteSelectionChange();
    }

    TSet<UBlueprintGeneratedClass*> FixedSCS;

    // in the case where we're replacing component instances, we need to make
    // sure to re-run their owner's construction scripts
    for (AActor* ActorInstance: OwnersToRerunConstructionScript)
    {
        // Before rerunning the construction script, first fix up the SCS if any component class has changed from actor to scene
        if (bFixupSCS)
        {
            UBlueprintGeneratedClass* BPGC = Cast<UBlueprintGeneratedClass>(ActorInstance->GetClass());
            while (BPGC && !FixedSCS.Contains(BPGC))
            {
                if (BPGC->SimpleConstructionScript)
                {
                    BPGC->SimpleConstructionScript->FixupRootNodeParentReferences();
                    BPGC->SimpleConstructionScript->ValidateSceneRootNodes();
                }
                FixedSCS.Add(BPGC);
                BPGC = Cast<UBlueprintGeneratedClass>(BPGC->GetSuperClass());
            }
        }

        // Skipping CDOs as CSs are not allowed for them.
        if (!ActorInstance->HasAnyFlags(RF_ClassDefaultObject))
        {
            ActorInstance->RerunConstructionScripts();
        }
    }

    if (GEditor)
    {
        // Refresh any editors for objects that we've updated components for
        for (UObject* BlueprintAsset: PotentialEditorsForRefreshing)
        {
            FBlueprintEditor* BlueprintEditor = static_cast<FBlueprintEditor*>(GEditor->GetEditorSubsystem<UAssetEditorSubsystem>()->FindEditorForAsset(BlueprintAsset, /*bFocusIfOpen =*/false));
            if (BlueprintEditor)
            {
                BlueprintEditor->RefreshEditors();
            }
        }
    }
}

void FBlueprintCompileReinstancer::ReconstructOwnerInstances(TSubclassOf<UActorComponent> ComponentClass)
{
    if (ComponentClass == nullptr)
    {
        return;
    }

    TArray<UObject*> ComponentInstances;
    GetObjectsOfClass(ComponentClass, ComponentInstances, /*bIncludeDerivedClasses =*/false);

    TSet<AActor*> OwnerInstances;
    for (UObject* ComponentObj: ComponentInstances)
    {

        UActorComponent* Component = CastChecked<UActorComponent>(ComponentObj);

        if (AActor* OwningActor = Component->GetOwner())
        {
            // we don't just rerun construction here, because we could end up
            // doing it twice for the same actor (if it had multiple components
            // of this kind), so we put that off as a secondary pass
            OwnerInstances.Add(OwningActor);
        }
    }

    for (AActor* ComponentOwner: OwnerInstances)
    {
        ComponentOwner->RerunConstructionScripts();
    }
}

void FBlueprintCompileReinstancer::VerifyReplacement()
{
    TArray<UObject*> SourceObjects;

    // Find all instances of the old class
    for (TObjectIterator<UObject> it; it; ++it)
    {
        UObject* CurrentObj = *it;

        if ((CurrentObj->GetClass() == DuplicatedClass))
        {
            SourceObjects.Add(CurrentObj);
        }
    }

    // For each instance, track down references
    if (SourceObjects.Num() > 0)
    {
        TFindObjectReferencers<UObject> Referencers(SourceObjects, nullptr, false);
        for (TFindObjectReferencers<UObject>::TIterator It(Referencers); It; ++It)
        {
            UObject* CurrentObject = It.Key();
            UObject* ReferencedObj = It.Value();
            FPlatformMisc::LowLevelOutputDebugStringf(TEXT("- Object %s is referencing %s ---"), *CurrentObject->GetName(), *ReferencedObj->GetName());
        }
    }
}
void FBlueprintCompileReinstancer::ReparentChild(UBlueprint* ChildBP)
{
    check(ChildBP);

    UClass* SkeletonClass            = ChildBP->SkeletonGeneratedClass;
    UClass* GeneratedClass           = ChildBP->GeneratedClass;

    const bool ReparentGeneratedOnly = (ReinstClassType == RCT_BpGenerated);
    if (!ReparentGeneratedOnly && SkeletonClass)
    {
        ReparentChild(SkeletonClass);
    }

    const bool ReparentSkelOnly = (ReinstClassType == RCT_BpSkeleton);
    if (!ReparentSkelOnly && GeneratedClass)
    {
        ReparentChild(GeneratedClass);
    }
}

void FBlueprintCompileReinstancer::ReparentChild(UClass* ChildClass)
{
    check(ChildClass && ClassToReinstance && DuplicatedClass && ChildClass->GetSuperClass());
    bool bIsReallyAChild           = ChildClass->GetSuperClass() == ClassToReinstance || ChildClass->GetSuperClass() == DuplicatedClass;
    const UBlueprint* SuperClassBP = Cast<UBlueprint>(ChildClass->GetSuperClass()->ClassGeneratedBy);
    if (SuperClassBP && !bIsReallyAChild)
    {
        bIsReallyAChild |= (SuperClassBP->SkeletonGeneratedClass == ClassToReinstance) || (SuperClassBP->SkeletonGeneratedClass == DuplicatedClass);
        bIsReallyAChild |= (SuperClassBP->GeneratedClass == ClassToReinstance) || (SuperClassBP->GeneratedClass == DuplicatedClass);
    }
    check(bIsReallyAChild);

    ChildClass->AssembleReferenceTokenStream();
    ChildClass->SetSuperStruct(DuplicatedClass);
    ChildClass->Bind();
    ChildClass->StaticLink(true);
}

void FBlueprintCompileReinstancer::CopyPropertiesForUnrelatedObjects(UObject* OldObject, UObject* NewObject, bool bClearExternalReferences, bool bForceDeltaSerialization /* = false */)
{
    InstancedPropertyUtils::FInstancedPropertyMap InstancedPropertyMap;
    InstancedPropertyUtils::FArchiveInstancedSubObjCollector InstancedSubObjCollector(OldObject, InstancedPropertyMap);

    UEngine::FCopyPropertiesForUnrelatedObjectsParams Params;
    Params.bAggressiveDefaultSubobjectReplacement = false;
    // During a blueprint reparent, delta serialization must be enabled to correctly copy all properties
    Params.bDoDelta                       = bForceDeltaSerialization || !OldObject->HasAnyFlags(RF_ClassDefaultObject);
    Params.bCopyDeprecatedProperties      = true;
    Params.bSkipCompilerGeneratedDefaults = true;
    Params.bClearReferences               = bClearExternalReferences;
    Params.bNotifyObjectReplacement       = true;
    UEngine::CopyPropertiesForUnrelatedObjects(OldObject, NewObject, Params);

    InstancedPropertyUtils::FArchiveInsertInstancedSubObjects InstancedSubObjSpawner(NewObject, InstancedPropertyMap);
}

FRecreateUberGraphFrameScope::FRecreateUberGraphFrameScope(UClass* InClass, bool bRecreate)
    : RecompiledClass(InClass)
{
    if (bRecreate && ensure(RecompiledClass))
    {
        BP_SCOPED_COMPILER_EVENT_STAT(EKismetCompilerStats_RecreateUberGraphPersistentFrame);

        const bool bIncludeDerivedClasses = true;
        GetObjectsOfClass(RecompiledClass, Objects, bIncludeDerivedClasses, RF_NoFlags);

        for (UObject* Obj: Objects)
        {
            RecompiledClass->DestroyPersistentUberGraphFrame(Obj);
        }
    }
}

FRecreateUberGraphFrameScope::~FRecreateUberGraphFrameScope()
{
    BP_SCOPED_COMPILER_EVENT_STAT(EKismetCompilerStats_RecreateUberGraphPersistentFrame);
    for (UObject* Obj: Objects)
    {
        if (IsValid(Obj))
        {
            RecompiledClass->CreatePersistentUberGraphFrame(Obj, false);
        }
    }
}