Allow to ignore 'Double requirement given' error

It would be nice if ‘Double requirement given: %s (already in %s, name=%r)’ could be made a warning optionally, as long as it does not result in a conflict.

My use case is tox, where ‘django’ is defined in the test env (with version restrictions), but also in a requirements file (which is meant to install the test env outside of tox):

pip install --pre pytest pytest-django six Django>=1.7,<1.8 -rtest_project/test_requirements.txt

This results in the following error:

Double requirement given: django (from -r test_project/requirements.txt (line 3)) (already in Django<1.8,>=1.7, name=‘django’)

[piotr-dobrogost]

@rbtcollins

So the underlying issue here is #988 - without that we can’t handle the interactions that occur dealing with multiply encountered references to the same distribution.

Unless all of these references are top level which is the case here 😃

[dstufft]

I’m closing this, the fundamental issue here is #988 and this will effectively be solved by solving that issue.