GAS: Crash on resizing FActiveGameplayEffectsContainer::AttributeValueChangeDelegates while executing a contained delegate

Game code can register listeners to when a GAS attribute changes value, for example by calling:

AbilitySystemComponent->GetGameplayAttributeValueChangeDelegate(SomeAttribute).AddLambda();

These delegates are managed inside the AbilitySystemComponent's FActiveGameplayEffectsContainer::AttributeValueChangeDelegates.

Currently it's unsafe to make register or unregister a change listener while executing such a delegate, as this can cause the container to be grown or shrunk (but not always depending on container slack or attribute already registered).

There are valid use cases for registering or unregistering attribute listeners upon observing an attribute change, for example for game features that should activate or deactivate when a value crosses a threshold. Health thresholds being a primary example, so GAS usability would benefit from allowing attribute value change delegate modification from within a listener.

FGenericPlatformMisc::RaiseException (GenericPlatformMisc.cpp:740)
FDebug::CheckVerifyFailedImpl2 (AssertionMacros.cpp:663)
TArray<T>::RangeCheck (Array.h:758)
TMulticastDelegateBase<T>::Broadcast<T> (MulticastDelegateBase.h:251)
TMulticastDelegate<T>::Broadcast (DelegateSignatureImpl.inl:956)
FActiveGameplayEffectsContainer::InternalUpdateNumericalAttribute (GameplayEffect.cpp:3730)
FActiveGameplayEffectsContainer::OnAttributeAggregatorDirty (GameplayEffect.cpp:3301)
UAbilitySystemComponent::OnAttributeAggregatorDirty (AbilitySystemComponent.cpp:1906)
Invoke<T> (Invoke.h:66)
UE::Core::Private::Tuple::TTupleBase<T>::ApplyAfter<T> (Tuple.h:309)
TBaseUObjectMethodDelegateInstance<T>::ExecuteIfSafe (DelegateInstancesImpl.h:665)
TMulticastDelegateBase<T>::Broadcast<T> (MulticastDelegateBase.h:254)
TMulticastDelegate<T>::Broadcast (DelegateSignatureImpl.inl:956)
FAggregator::BroadcastOnDirty (GameplayEffectAggregator.cpp:663)
FActiveGameplayEffectsContainer::SetAttributeBaseValue (GameplayEffect.cpp:3781)
UAbilitySystemComponent::SetNumericAttributeBase (AbilitySystemComponent.cpp:388)<-- game code functions -->