error TS6059: File 'FolderA/FolderB/fileB.ts' is not under 'rootDir' 'FolderA/FolderB/FolderC'. 'rootDir' is expected to contain all source files.
  The file is in the program because:
    Root file specified for compilation


!!! error TS6059: File 'FolderA/FolderB/fileB.ts' is not under 'rootDir' 'FolderA/FolderB/FolderC'. 'rootDir' is expected to contain all source files.
!!! error TS6059:   The file is in the program because:
!!! error TS6059:     Root file specified for compilation
==== FolderA/FolderB/FolderC/fileC.ts (0 errors) ====
    class C {
    }
    
==== FolderA/FolderB/fileB.ts (0 errors) ====
    /// <reference path='FolderC/fileC.ts'/>
    class B {
        public c: C;
    }
    