On Sun, Jul 8, 2018, 04:25 Paul Moore <p.f.moore@gmail.com> wrote:

In principle, I'm 100% on board with this. However, as is typical with
packaging changes, we have a huge backward compatibility situation to
address - the many packages on PyPI that are infrequently updated or
maintained and yet still in common use. We also have a large body of
users who build pip into their internal workflows, who often rely
heavily on what to "normal pip usage" are obscure edge cases. I'd like
to find some way of assessing the impact before we simply switch to
full build isolation (we've already had a fair number of bug reports
on pip that are triggered by build isolation, such as the ones that
started this discussion).

I think it would be helpful for this discussion if we could look at these bug reports – do does anyone have links?

Every new rollout will cause some issues. The crucial thing IME is to see whether they're bugs in the implementation we can fix, whether there's a simple way to improve error messages for other cases, ... etc. If they're intractable issues that's very different than if they're teething pains :-)