Actually, from what I can see in VS2017 solution files, a Solution Folder is now created IN the .sln file. So, if you add a project of name "TestFolder" - you'll have a project in the .sln of that name. Trying to add in a Solution Folder (which is only a virtual folder in the file system) VS won't let you add a same named project.
This is the SLN contents of a solution with ONLY a Solution Folder in it.
Microsoft Visual Studio Solution File, Format Version 12.00
Actually, from what I can see in VS2017 solution files, a Solution Folder is now created IN the .sln file. So, if you add a project of name "TestFolder" - you'll have a project in the .sln of that name. Trying to add in a Solution Folder (which is only a virtual folder in the file system) VS won't let you add a same named project.
This is the SLN contents of a solution with ONLY a Solution Folder in it.
Microsoft Visual Studio Solution File, Format Version 12.00
Visual Studio 15
VisualStudioVersion = 15.0.28307.645
MinimumVisualStudioVersion = 10.0.40219.1
Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "TestFolder", "TestFolder", "{01F7F854-0EC2-47D2-AF62-97CAC80C3294}"
EndProject
Global
GlobalSection(SolutionProperties) = preSolution
HideSolutionNode = FALSE
EndGlobalSection
GlobalSection(ExtensibilityGlobals) = postSolution
SolutionGuid = {5E6FC95B-7995-413A-A37A-102F5797AEF0}
EndGlobalSection
EndGlobal