[BUG - Release] TArray function params are always 0 elements

[Spectre-Cular]

Branch or Release UE4SS - v3.0.1 Beta #0 - Git SHA #666b477 UE4SS Build Configuration: GameShippingWin64 (MSVC)

Game and Engine Version Palworld Dedicated Server build #14342103 Palworld v0.2.4.0 UE 5.2.1

Describe the bug When trying to use reflection to grab the data from a TArray function parameter, Num() returns 0 elements

Mods directory ArrayBug.zip

To Reproduce Steps to reproduce the behavior:

1. Compile a C++ mod with the following:

   auto on_unreal_init() -> void override
   {
   Hook::RegisterProcessLocalScriptFunctionPostCallback([](UObject* Context, FFrame& Stack, ...) {
       if (Stack.Node()->GetName() == STR("SomeCPPFunc")) {
           struct Params {
               TArray<FString> Array;
           };
   
           auto params = (Params*)Stack.Locals();
           Output::send<LogLevel::Verbose>(STR("Iterating TArray of Length {}\n"), params->Array.Num());
           for (auto& arrElem : params->Array)
               Output::send<LogLevel::Verbose>(STR("{}\n"), arrElem.GetCharArray());
       }
   });
   }

2. Compile and package a BP mod with the following:

3. In UE4SS debugging tools console, you can see Iterating TArray of Length 0 and no actual elements are printed

Expected behavior Console should print Iterating TArray of Length 4 followed by Elem1, Elem2, Elem3 and Elem4

Desktop (please complete the following information):

• OS: Win10

Additional context Original Discord conversation

[Yangff]

It turns out that all arrays in BP will be treated as a CPF_OutParm. No matter how you set it up in the editor (if you can even change it)

https://github.com/EpicGames/UnrealEngine/blob/c830445187784f1269f43b56f095493a27d5a636/Engine/Source/Editor/Kismet/Private/BlueprintCompilationManager.cpp#L3051

As a result, the address is found inside FFrame::OutParms (which is a linked list) instead of the Locals. You can iterate over it with Out->NextOutParm and, in theory the address should locate in one of the Out->PropAddr. In your case, I think it should be the first one.