I had been using Visual studio for Mac with C# 7.0. I've recently updated and now version 7 isn't working.
Specifically, I'm now getting errors like this:
/Users/tonyvalenti/Projects/TonyValenti/Clio.WebDav.git/AlphaDrive.Mac/CSC: Error CS1617: Invalid -langversion option
7'. It must be ISO-1', `ISO-2', Default or value in range 1 to 6 (CS1617) (AlphaDrive.Mac)