Basically this:
- I created a fresh project in Visual Studio 2019 using the VSX c# template.
- I moved a bunch of files from an older VSX project (for VS 17).
- I compiled and ran the project - errors started emerging.
- I addressed one error, ran the project - got another error.
- I started addressing the second error and in the process of fixing it I noticed that now VS is for some reason compiling an unknown external project whenever I run my project. I realized it because once the program hit the error and instead of jumping into my code and showing me the line, it showed me this message: "The source file is different from when the module was built. Would you like the debugger to use it anyway?" Also whenever I changed something in my code files now - the changes never apply. Moreover, the first error (which I have already fixed) resurfaced again, and when the debugger tried showing me the place of the error - it clearly used the new file, thinking that it's an old one (even if I change the new file to have empty space in the line where the error was, the debugger will still stand on that empty line, talking about the error).
- Now whenever I create a new VSX project, even an empty one, and compile/run it - the studio runs that unidentified external project (I have absolutely no clue where that project is, even the files that the debugger uses have no influence on that project.
UPDATE: I deleted Visual Studio cache folders (C:\Users\xxx\AppData\Local\Microsoft\VisualStudio\16.0_xxxx) as well as reset the experimental Visual studio with the start menu prompt "Reset Visual Studio 2019 Experimental Instance". Now, when I compile my VSX projects, a clean and empty Visual Studio instance is launched - my extension code is ignored.