Mac build issue, UE 4.16, Xcode: Expected *.h to be first header included

[bcbrock]

I'm building the UnrealEngine 4.16.1 itself and the UnrealCV master source code together from XCode on Mac OS 10.12.2. It seems that all of the UnrealCV headers get a compile error in this environment:

Parsing headers for UE4Editor
  Running UnrealHeaderTool UE4Editor "/Users/bcbrock/UnrealEngine/Engine/Intermediate/Build/Mac/UE4Editor/Development/UE4Editor.uhtmanifest" -LogCmds="loginit warning, logexit warning, logdatabase error" -Unattended -WarningsAsErrors
Reflection code generated for UE4Editor in 10.8587898 seconds
/Users/bcbrock/UnrealEngine/Engine/Plugins/UnrealCV/Source/UnrealCV/Private/CaptureManager.cpp(1): error: Expected CaptureManager.h to be first header included.
/Users/bcbrock/UnrealEngine/Engine/Plugins/UnrealCV/Source/UnrealCV/Private/CommandDispatcher.cpp(1): error: Expected CommandDispatcher.h to be first header included.
/Users/bcbrock/UnrealEngine/Engine/Plugins/UnrealCV/Source/UnrealCV/Private/ConsoleHelper.cpp(1): error: Expected ConsoleHelper.h to be first header included.
/Users/bcbrock/UnrealEngine/Engine/Plugins/UnrealCV/Source/UnrealCV/Private/ExecStatus.cpp(1): error: Expected ExecStatus.h to be first header included.
/Users/bcbrock/UnrealEngine/Engine/Plugins/UnrealCV/Source/UnrealCV/Private/GTCaptureComponent.cpp(1): error: Expected GTCaptureComponent.h to be first header included.
/Users/bcbrock/UnrealEngine/Engine/Plugins/UnrealCV/Source/UnrealCV/Private/ObjectPainter.cpp(1): error: Expected ObjectPainter.h to be first header included.
/Users/bcbrock/UnrealEngine/Engine/Plugins/UnrealCV/Source/UnrealCV/Private/PlayerViewMode.cpp(1): error: Expected PlayerViewMode.h to be first header included.
/Users/bcbrock/UnrealEngine/Engine/Plugins/UnrealCV/Source/UnrealCV/Private/ScreenCapture.cpp(1): error: Expected ScreenCapture.h to be first header included.
/Users/bcbrock/UnrealEngine/Engine/Plugins/UnrealCV/Source/UnrealCV/Private/ServerConfig.cpp(1): error: Expected ServerConfig.h to be first header included.
/Users/bcbrock/UnrealEngine/Engine/Plugins/UnrealCV/Source/UnrealCV/Private/TcpServer.cpp(1): error: Expected TcpServer.h to be first header included.
/Users/bcbrock/UnrealEngine/Engine/Plugins/UnrealCV/Source/UnrealCV/Private/UE4CVGameMode.cpp(1): error: Expected UE4CVGameMode.h to be first header included.
/Users/bcbrock/UnrealEngine/Engine/Plugins/UnrealCV/Source/UnrealCV/Private/UE4CVServer.cpp(1): error: Expected UE4CVServer.h to be first header included.
/Users/bcbrock/UnrealEngine/Engine/Plugins/UnrealCV/Source/UnrealCV/Private/ViewMode.cpp(1): error: Expected ViewMode.h to be first header included.
/Users/bcbrock/UnrealEngine/Engine/Plugins/UnrealCV/Source/UnrealCV/Private/Commands/ActionHandler.cpp(1): error: Expected ActionHandler.h to be first header included.
/Users/bcbrock/UnrealEngine/Engine/Plugins/UnrealCV/Source/UnrealCV/Private/Commands/AliasHandler.cpp(1): error: Expected AliasHandler.h to be first header included.
/Users/bcbrock/UnrealEngine/Engine/Plugins/UnrealCV/Source/UnrealCV/Private/Commands/CameraHandler.cpp(1): error: Expected CameraHandler.h to be first header included.
/Users/bcbrock/UnrealEngine/Engine/Plugins/UnrealCV/Source/UnrealCV/Private/Commands/ObjectHandler.cpp(1): error: Expected ObjectHandler.h to be first header included.
/Users/bcbrock/UnrealEngine/Engine/Plugins/UnrealCV/Source/UnrealCV/Private/Commands/PluginHandler.cpp(1): error: Expected PluginHandler.h to be first header included.
/Users/bcbrock/UnrealEngine/Engine/Plugins/UnrealCV/Source/UnrealCV/Private/libs/cnpy.cpp(1): error: Expected cnpy.h to be first header included.
Build canceled.
Command /Users/bcbrock/UnrealEngine/Engine/Build/BatchFiles/Mac/Build.sh failed with exit code 1

This error is apparently due to a recent UnrealEngine feature called "Insert What You Use" (IWYU). A quick fix is to modify UnrealCV.Build.cs:

diff --git a/Source/UnrealCV/UnrealCV.Build.cs b/Source/UnrealCV/UnrealCV.Build.cs
index 1a395ee..ebf01f2 100644
--- a/Source/UnrealCV/UnrealCV.Build.cs
+++ b/Source/UnrealCV/UnrealCV.Build.cs
@@ -7,6 +7,8 @@ namespace UnrealBuildTool.Rules
 	{
 		public UnrealCV(TargetInfo Target)
 		{
+			bEnforceIWYU = false;
+
 			// This trick is from https://answers.unrealengine.com/questions/258689/how-to-include-private-header-files-of-other-modul.html
 			string EnginePath = Path.GetFullPath(BuildConfiguration.RelativeEnginePath);

Interestingly, this error does not occur when I build the UnrealCV plugin with build.sh, only when built under XCode.

[qiuwch]

Cooool. Thanks for reporting this.

Do you want to make a pull request to update the Build.cs, so that github can track your contribution?
Or I can also do that.

[bcbrock]

Please feel free to make this change yourself. Technically I would be required to go through a formal legal process if I do anything beyond opening issues :-)

[qiuwch]

I see, I did not expect this can cause a trouble for you. I will do it. Thanks.

[qiuwch]

I am traveling now and will update it when I am back. I need to do a little testing to make sure it won't break the compilation of other UE4 versions.

[doublerebel]

Related: #55