I am trying to provide an alias for a dll plugin (System.Threading.dll). I have read that you should be able to do this by adding the alias to a rsp file. This appears to work for others but I have had zero luck so far. There is conflicting information about the naming of this rsp file. On older versions of Unity it looks like "smcs.rsp" should be used, but on newer versions maybe it should be "mcs.rsp" or "gmcs.rsp". I have tried all three on Unity 5.5, Unity 2017.3, and Unity 2018.2. Within each file this is what I have written: -reference:CustomThreadingLibrary=Assets/Plugins/System.Threading.dllWhere CustomThreadingLibrary is the alias and Assets/Plugins/System.Threading.dll is the file I want to alias. In my code I should be able to write this at the top: extern alias CustomThreadingLibrary;however this just produces the error: The extern alias 'CustomThreadingLibrary' was not specified in a /reference optionI made sure the code recompiled after creating the files. Any help would be greatly appreciated.