Never break the build again with an organized code base

During my time developing for different companies one of the most common daily scenarios I encounter is helping a developer debug code. Going to some method’s definition, only to realize they can only view metadata and not actual code. The library is still internal, most likely developed by another department inside the same organization, however, it was added as an external DLL reference and to view the code they need to open another solution in another folder. Well this will work until the external code has been updated and since code is updated daily, the references must also be updated or the code base quickly goes out of sync, not to mention debugging the external binaries is very difficult.