Lua: fix non-const TArray outparams being skipped in UFunction property pushers

[Lyrth]

Description

UFunction parameters that has type TArray<...>& discards the value passed from Lua for it, making the UFunction receive an empty array, or shifts the argument list and messes up parameter ordering.

Type of change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

/Script/Engine.KismetStringLibrary:CullArray and /Script/UMG.WidgetBlueprintLibrary:GetAllWidgetsOfClass are used to check if the parameters were passed correctly, by hooking into them and calling them from Lua.

Testing

Test code:

-- int32 CullArray(FString SourceString, TArray<FString>& inArray)
RegisterHook("/Script/Engine.KismetStringLibrary:CullArray", function (Context, SourceString, InArray)
    print(">> CullArray call")

    local str = SourceString:get()
    print(("String: '%s'"):format(str:ToString()))

    local arr = InArray:get()
    print(("Array: __len %d, num %d, %016x %016x"):format(#arr, arr:GetArrayNum(), arr:GetArrayAddress(), arr:GetArrayDataAddress()))
    for i = 1, #arr do
        print("  "..i, arr[i]:ToString())
    end

    print("<< CullArray")
    print()
end)

-- void GetAllWidgetsOfClass(class UObject* WorldContextObject, TArray<class UUserWidget*>& FoundWidgets, TSubclassOf<class UUserWidget> WidgetClass, bool TopLevelOnly);
RegisterHook("/Script/UMG.WidgetBlueprintLibrary:GetAllWidgetsOfClass", function (Context, WorldContextObject, FoundWidgets, WidgetClass, TopLevelOnly)
    print(">> GetAllWidgetsOfClass call")

    local world = WorldContextObject:get()
    print(("World: '%s'"):format(world))

    local arr = FoundWidgets:get()
    print(("Array: __len %d, num %d, %016x %016x"):format(#arr, arr:GetArrayNum(), arr:GetArrayAddress(), arr:GetArrayDataAddress()))

    local class = WidgetClass:get()
    print(("Class: '%s'"):format(class))

    local bool = TopLevelOnly:get()
    print(("TopLevelOnly: '%s'"):format(bool))

    print("<< GetAllWidgetsOfClass")
    print()
end)



ExecuteInGameThread(function()
    local ksl = StaticFindObject("/Script/Engine.Default__KismetStringLibrary")

    local arr = {
        "aaa",
        "bbb",
        "",
        "world",
        "",
        "",
        "ccc"
    }
    print("** Before cull:")
    for i = 1, #arr do
        print("  "..i, arr[i])
    end
    print()

    local elLeft = ksl:CullArray("hello", arr)
    ---@cast arr RemoteUnrealParam<FString>

    print("** After cull:")
    for i = 1, elLeft do
        print("  "..i, arr[i]:get():ToString())
    end

    print("----------")
    print()
end)

ExecuteInGameThread(function()
    local wbl = StaticFindObject("/Script/UMG.Default__WidgetBlueprintLibrary")

    local world = require "UEHelpers".GetWorld()
    local widget = StaticFindObject("/Script/UMG.UserWidget")
    local foundArr = { }

    for _ = 1,69 do StaticConstructObject(widget, world) end

    wbl:GetAllWidgetsOfClass(world, foundArr, widget, false)

    print("** Found widgets: ", #foundArr)
    print("----------")
    print()
end)

Original behavior:

This change:

Checklist

• I have added the necessary description of this PR to the changelog, and I have followed the same format as other entries.

Notes

A similar change (and also to line 249) may be needed once TMap and TSet support gets in.