Native Blueprint Code generations create wrong includes

Development Programming & Scripting Blueprint
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1

Hello guys, hope this will be helpful :slight_smile:

Bug description

In my project i tried for the first time the blueprint nativization procedure, and it failed strangely. Digging it, i found out that it was generating the wrong includes for the blueprints.

In fact, it was skipping a parent include for some classes, for example if i had:

  1. C++ class named A
  2. BlueprintClass named B, derived from A
  3. BlueprintClass named C, derived from B

int the C class header it was correctly extending B, but it was including A directly, resulting in a compiling failure (unknown class B).

I had an hard time reproducing it on a fresh project, below you can find the steps.

It’s kinda hard to reproduce it, but this way it fails most of the times.

How to reproduce

Note: Since testing it requires packaging, i suggest to disable “Full rebuild”: i tested with it too, the result is the same.

Note 2: This steps list will show a setup for a working project, then will show how to mess it up, and how to workaround it.

Tested on 4.15.1-0

Initial setup to a working project:

  • Create a new “C++ Basic Code” project, name it “NativeTesting”: Desktop, maximum quality and no starter content
  • Build the newly created project in VS
  • Open the editor
  • Create a new C++ class, based on StaticMeshActor, and call it “MyStaticMeshActor”.
  • The following code will be generated, we’ll leave it as it is:

MyStaticMeshActor.h

  // Fill out your copyright notice in the Description page of Project Settings.

#pragma once

#include "Engine/StaticMeshActor.h"
#include "MyStaticMeshActor.generated.h"

/**
 * 
 */
UCLASS()
class NATIVETEST_API AMyStaticMeshActor : public AStaticMeshActor
{
	GENERATED_BODY()
	
};

MyStaticMeshActor.cpp

// Fill out your copyright notice in the Description page of Project Settings.

#include "NativeTest.h"
#include "MyStaticMeshActor.h"
  • Close the editor and recompile
  • Now return to editor, and create a new blueprint class, with “MyStaticMeshActor” as parent, and call it “MyBase”. Open it, save, close.
  • Create a new blueprint class, with “MyBase” as parent, and call it “SecondBP”. Open it.
  • Add a cube component, save and close.
  • Put it in the level, and save it with name “MyLevel”
  • Open Project Settings, and go to Packaging section
  • Set BuildConfiguration to Development, uncheck “Full Rebuild”, and under blueprints set Nativization Method to “Inclusive”
  • Package the project for windows 64: it will work successfully.

Create the problem:

  • Open Project Settings, and go to Packaging section

  • Under blueprints set Nativization Method to “Exclusive”

  • Open “SecondBP”, go to class settings and enable “Nativize”

  • Try to package again.

  • it should fail with errors like these:

    UATHelper: Packaging (Windows (64-bit)): UnrealBuildTool: U:\Unreal Projects\NativeTesting\Intermediate\WindowsNoEditor\NativizedAssets\Source\NativizedAssets\Public\SecondBP__pf1010915279.h(8): error C2504: ‘AMyBase_C__pf1010915279’: base class undefined
    UATHelper: Packaging (Windows (64-bit)): UnrealBuildTool: U:\Unreal Projects\NativeTesting\Intermediate\WindowsNoEditor\NativizedAssets\Source\NativizedAssets\Public\SecondBP__pf1010915279.h(10): error C3646: ‘Super’: unknown override specifier

In fact, looking at the generated code, in Intermediate/WindowsNoEditor/NativizedAssets/Source/Public/SecondBP__****.h, we have:

#include "Blueprint/BlueprintSupport.h"
#include "NativeTesting/MyStaticMeshActor.h"
class UStaticMeshComponent;
#include "SecondBP__pf1010915279.generated.h"
UCLASS(config=Engine, Blueprintable, BlueprintType, meta=(ReplaceConverted="/Game/SecondBP.SecondBP_C", OverrideNativeName="SecondBP_C"))
class ASecondBP_C__pf1010915279 : public AMyBase_C__pf1010915279
{

[…]

Notice how it’s including MyStaticMeshActor.h instead of MyBase_C__pf1010915279.h

Workaround:

  • Open the blueprint “MyBase”
  • Connect something to “BeginPlay”, like a “Print String” node, save and close (this will make it a “normal blueprint”, not a data-only).
  • Try to package again, it will work.

Current Behaviour

On exclusive nativization, seems like it fails to generate the correct includes if the parent is a data-only blueprint.
In fact, in the SecondBP_****.h it places:

#include "NativeTesting/MyStaticMeshActor.h"

instead of:

#include "MyBase__pf1010915279.h"

As already stated, it seems directly related to data-only blueprint, but it doesn’t happen on an inclusive nativization.

Expected behaviour

It should always generate the correct include (with the right parent class).

Conclusions

I had an hard time tackling this, it seemed pretty randomic, and i lost a lot of time due to the numerous packaging launches.

I noticed that sometimes it still work, but trying around i can always make it fail in the same way (this is the simplest i found).

I hope this can help you, and maybe others that had issues like me, with the workaround.

Let me know if you need more infos :slight_smile:

Simone Daminato

[edit1] : fixed some typos.

2

Hey

Thank you for submitting a bug report. I have reproduced this issue and logged a report for it here Unreal Engine Issues and Bug Tracker (UE-44488) . You can track the report’s status as the issue is reviewed by our development staff. Please be aware that this issue may not be prioritized or fixed soon.

Cheers

3

Thanks a lot .
I found another small issue of nativization with Arrays of TSubclassOf.
Do you prefer if i report it in here or open another thread?

4

It would be best to create a new post to track each issue separately.