[UE 4.8.2] Suddenly bad #include in read-only .h

It is WidgetBlueprint.h with it’s #include “Blueprint/WidgetBlueprintGeneratedClass.h”

I need function, that takes big amount of arguments and returns struct. Easiest way for me is make UWidgetBlueprint-derived class and reparent one little blueprint, so i can use C++ function i made in this blueprint. I created this class, there was .h i needed, but no such luck! Now I’am getting compiler error:
CompilerResultsLog:Error: Error H:\Lavrenty\UE4\UE4ItSelf\Unreal Engine\4.8\Engine\Source\Editor/UMGEditor/Public/WidgetBlueprint.h(4) : fatal error C1083: Cannot open include file: ‘Blueprint/WidgetBlueprintGeneratedClass.h’: No such file or directory
It does make no sense, because it compiled fine before, but now, when somewhere included “WidgetBlueprint” (real path is way longer), compiler throws error above. When i removed .cpp and .h of my new class everything compiled fine.

How engine has been compiled with bad #include?

Has you regenerated the project files?

No, because i even don’t know how to do this.

Just right click on your .uproject file and select regenerate project files.