ERROR “swiftc failed with exit code 1” when converting to latest syntax

Question

I was trying to convert syntax of old Swift project to new one as per few suggestion on Stack Overflow I tried converting it through Edit > Convert > To latest Synta

Answer 1

Had the same issue but with duplicate file references. Deleting Derived Data and cleaning had no success. But I got it fixed by doing this:

Navigate to your project.pbxproj -> open with your text editor of choice(I use atom).

Command+F and find the duplicate file sources and then delete them.

Build/Run and should be fixed.