Comment 7 for bug 1906322

same issue.

pip 21.0.1 from /opt/stack/.local/lib/python3.8/site-packages/pip (python 3.8)
VERSION="20.04.2 LTS (Focal Fossa)"

victoria branch.

DEPRECATION: Constraints are only allowed to take the form of a package name and a version specifier. Other forms were originally permitted as an accident of the implementation, but were undocumented. The new implementation of the resolver no longer supports these forms. A possible replacement is replacing the constraint with a requirement.. You can find discussion regarding this at https://github.com/pypa/pip/issues/8210.
ERROR: Links are not allowed as constraints