Description of problem:
dnf needs pyliblzma in order to decompress xz repodata, but dnf doesn't Require pyliblzma.
Version-Release number of selected component (if applicable):
Steps to Reproduce:
1. dnf remove pyliblzma
2. dnf grouplist
Error: No group data available for configured repositories.
Took me a while to figure out that the error message actually means that dnf silently failed to decompress the comps.xml.xz and therefore it sees no groups.
Thank you for reporting this.
Fixed by 98a9b09.