pip can break anytime, even dependencies of your dependencies can break if they were not pinned correctly (by their maintainers, not you).
cannot import name SourceDistribution
You are now unable to install anythnig, nor to downgrade or upgrade pip itself (to 20.0.1 or 19).
Failing during a deployment (again): Could not find suitable distribution for Requirement.parse("termcolor==1.1.0")
googleapis/google-cloud-python#3757
this problem seem to be caused by having a from future import unicode_literals in setup.py
LOL. Fixed by better pinning dependencies (of dependencies).
Quicklisp: no issues so far (5 years+) :D
And I build binaries of my software, so deployments don't even need to download stuff.