Building the GameLift Server SDK plugin for Unreal Engine versions greater than 4.21

In the past, I have not dealt with any errors while building the plugin when I add it on a per-project basis, meaning I usually add the plugin to a Plugin folder in my Unreal projects rather than Unreal Engine's Engine\Plugins folder. I have made a somewhat similar post about suppressing some warnings, but now I want to address how to solve actual compiler errors in addition to warnings when you try to add the plugin to Unreal Engine itself. And again, I am not sure at all why this only happens when adding the plugin directly to the engine as opposed to adding the plugin to individual projects.

Assuming you are using the plugin in the UE4.21.1 folder in GameLift_09_03_2019\GameLift-SDK-Release-3.4.0\GameLift-Unreal-plugin-3.3.0,

First, to remove the "Refrenced directory ... does not exist" warnings in GameLiftServerSDK.Build.cs, replace the first two lines in the GameLiftServerSDK constructor,

PublicIncludePaths.AddRange(
    new string[] {
    "GameLiftServerSDK/Public"
    }
);  

PrivateIncludePaths.AddRange(
    new string[] {
    "GameLiftServerSDK/Private",
    }
);

with

PublicIncludePaths.Add(System.IO.Path.Combine(ModuleDirectory, "Public"));
PrivateIncludePaths.Add(System.IO.Path.Combine(ModuleDirectory, "Private"));

Next, there are also two instances of this line, PublicLibraryPaths.Add(SDKDirectory); causing compiler warnings because PublicLibraryPaths is obsolete in newer versions of Unreal Engine, so you can either replace each instance of this line with PublicAdditionalLibraries.Add(SDKDirectory); or with PublicSystemLibraries.Add(SDKDirectory);. Or you can even get rid of each instance of that line altogether.

Moving on to actual compiler errors, in GameLiftServerSDK.h, some of the include statements are incorrect. For example, #include "ModuleManager.h" should be #include "Modules/ModuleManager.h"

#include "DelegateCombinations.h" should be #include "Delegates/DelegateCombinations.h"

#include "AllowWindowsPlatformTypes.h" should be #include "Windows/AllowWindowsPlatformTypes.h"

"#include "HideWindowsPlatformTypes.h" should be #include "Windows/HideWindowsPlatformTypes.h"

Similarly in GameLiftServerSDK.cpp, the following include statement should be fixed,

#include "ModuleManager.h" should be #include "Modules/ModuleManager.h"

#include "IPluginManager.h" should be #include "Interfaces/IPluginManager.h"

There is also an include statement missing in GameLiftServerSDK.cpp, the include for its own header file. And this include statement has to be the very first include statement in this cpp file,

#include "GameLiftServerSDK.h"

Lastly, there is an include statement #include "Core.h" that may trigger a compiler warning related to IWYU, because it is not recommended to import monolithic header files, but I have not found a workaround for this.

I will update this post appropriately if I find anything new, but hope this helps people who are experiencing issues when trying to build the UE4 plugin for versions of Unreal Engine greater than 4.21.