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

For me, it was the keychainAccess problem as described in this answer (my error messages were completely opaque, all I had to go by was 'failed with exit code 1')