On closer inspection I noticed that in fedora-28.repo had mirrorlist=https://mirrors.fedoraproject.org/metalink?repo=28&arch=$basearch which did not lead to a valid mirrorlist but https://mirrors.fedoraproject.org/metalink?repo=fedora-28&arch=$basearch did. So I edited it and it worked.
I was trying to build Atomic workstation locally when I discovered what I believe to be a bug in f28 branch.
I executed
rpm-ostree compose tree --repo=repo workstation-ostree-config/fedora-ostree-workstation.jsonbut it failed withOn closer inspection I noticed that in fedora-28.repo had mirrorlist=https://mirrors.fedoraproject.org/metalink?repo=28&arch=$basearch which did not lead to a valid mirrorlist but https://mirrors.fedoraproject.org/metalink?repo=fedora-28&arch=$basearch did. So I edited it and it worked.
Sending this PR to have it fixed.