Hi folks,
I find out a problem with a comps in repo Fedora 27 Updates (see http://mirror.vutbr.cz/fedora/updates/27/x86_64/repodata/). The file has got zero size.
F26 is OK.

And DNF fails with error "Fatal parser error".

dnf install @buildsys-build
Traceback (most recent call last):
File "/bin/dnf", line 58, in
main.user_main(sys.argv[1:], exit_code=True)
File "/usr/lib/python3.6/site-packages/dnf/cli/main.py", line 179, in user_main
errcode = main(args)
File "/usr/lib/python3.6/site-packages/dnf/cli/main.py", line 64, in main
return _main(base, args, cli_class, option_parser_class)
File "/usr/lib/python3.6/site-packages/dnf/cli/main.py", line 99, in _main
return cli_run(cli, base)
File "/usr/lib/python3.6/site-packages/dnf/cli/main.py", line 115, in cli_run
cli.run()
File "/usr/lib/python3.6/site-packages/dnf/cli/cli.py", line 1014, in run
return self.command.run()
File "/usr/lib/python3.6/site-packages/dnf/cli/commands/install.py", line 108, in run
self.base.read_comps(arch_filter=True)
File "/usr/lib/python3.6/site-packages/dnf/base.py", line 550, in read_comps
self._comps._add_from_xml_filename(decompressed)
File "/usr/lib/python3.6/site-packages/dnf/comps.py", line 328, in _add_from_xml_filename
ret = comps.fromxml_f(fn)
_libpycomps.ParserError: Fatal parser error