This simple lua scriplet

 %transfiletriggerin -p <lua> -- %{_mandir}
 if posix.getcwd() != '/' then
     print("Hello")
 endif

cause:

[    4s] + exec rpmbuild -ba --define '_srcdefattr (-,root,root)' --noclean
--nosignature --define '_build_create_debug 1'
/home/abuild/rpmbuild/SOURCES/man.spec
[    4s] error: invalid syntax in lua scriptlet: [string
"%transfiletriggerin"]:1: 'then' expected near '!'


... accordingly to /usr/share/doc/packages/rpm/manual/lua.md the syntax is
correct ...

I'd like to use the return value of

  stat = posix.stat("/var/cache/man")

to test is /var/cache/man exists and is also a directory but the string compare

  stat.type != "directory"

crashes with a similar error