Engine build fails due to Unresolved External Symbol error after adding a new global variable to the Engine and then trying to reference it within Engine code

Building the Engine in Visual Studio will fail due to an unresolved external symbol error if a new global variable is added to CoreGlobals.h and then referenced elsewhere in the Engine code. The build will only complete successfully if a full rebuild is performed.

1. Open the UE4 solution in Visual Studio.
2. Locate and open the CoreGlobals.h file.
   • Engine/Source/Runtime/Core/Public/CoreGlobals.h
3. Add a new global boolean variable to the file.
   • eg: extern CORE_API bool GIsTestGlobal;
4. Build the UE4 project.
5. Once the build completes, locate and open the SceneComponent.cpp file
   • Engine/Source/Runtime/Engine/Private/Components/SceneComponent.cpp
6. Locate the DetachFromComponent() function.
7. Add an if check for the new global variable added in step 3.
   • eg: if (GIsTestGlobal)
8. Build the UE4 project.

RESULT:
The build will fail with an unresolved external symbol error similar to the following

error LNK2001: unresolved external symbol "__declspec(dllimport) bool GIsTestGlobal" (__imp_?GIsTestGlobal@@3_NA)

EXPECTED:
The build completes successfully.

WORKAROUND:
Perform a full rebuild of the UE4 project.