Support PyPy3 v5.2

[jayvdb]

PyPy has started releasing alpha releases of PyPy3 v5.2, and Travis now supports python: pypy3.3-5.2-alpha1.

PyPy3 v5.2 depends on virtualenv>=15.0.2, whereas Travis installs 12.0.6. Only force the use of virtualenv>=15.0.2 on PyPy3 v5.2, so that existing users of tox-travis are not impacted. This is complicated by Travis providing setuptools 12.0.5, which does not support platform_python_implementation=="PyPy" as an environment marker, and fails to install tox-travis from a source tarball. However tox-travis provides a universal wheel, which supports that environment marker, and Travis pip 6.0.7 can install it.

This change breaks any use of tox-travis with old setuptools. As tox-travis uses tox to install and test the package, either we use skipdist=True or tell tox to use a wheel to install tox-travis, thereby avoiding setuptools in tox.

Also, fiddle with tox internals so that it attempts to run python for the Travis versions pypy3.3-5.2-*.

Fixes #22

[jayvdb]

I have yet to add tests for the code changes.

I would appreciate it if you could first upload this to https://testpypi.python.org/pypi , then we can double check that pip install --index-url "https://testpypi.python.org/pypi" tox-travis works on Travis, without attempting to use the old setuptools, and any other scenarios we think people might actually be using.
I am assuming that nobody is putting tox-travis in their setup.py install_requires, or if they do then they can upgrade setuptools themselves.

I have avoided using setup_requires, as everything I read about it says it causes more obscure bugs than it solves. I could add a PEP 518 pyproject.toml , however pip and setuptools dont support that yet.
pypa/pip#3691
pypa/setuptools#651

[ryanhiebert]

This is excellent work. I'm learning a lot from reviewing it, thank you. I'll probably take a couple more days to figure it all out (not enough time available to review quickly), so don't think I'm ignoring you. You've also requested that I test this on testpypi before I merge it, so I'll do that too.

[jayvdb]

Nod. Im happy for this one to be done slowly and carefully.
Need to check the min tox version.

[jayvdb]

Confirmed the tox min version is still 2.0 . Here is the last change related to tox.config.default_factors, occurring in the 2.0 dev releases.
https://bitbucket.org/hpk42/tox/commits/5fbd833e8b0e88cf71920a147

[ryanhiebert]

Thank you for checking on that.

[jayvdb]

Here is a nice breakdown of the problem with detecting PyPy:
pypa/packaging#72 (comment)

I have independently found that ~18+ is the min that supports platform_python_implementation
https://travis-ci.org/jayvdb/tox-travis/builds/144847778

However my testing shows that platform.python_implementation is 20+
https://travis-ci.org/jayvdb/tox-travis/builds/144854169

And python_implementation (which I didnt know about ...) is strange - it works for setup.py build_wheel , but then fails for tox installing the wheel in pkg_resources/_markerlib (not packaging) https://travis-ci.org/jayvdb/tox-travis/builds/144860056 , so I think that python_implementation is 100% off the table for tox-travis (unless we fiddle with the wheel to replace python_implementation with platform_python_implementation after setuptools has created it.... interesting...).

We still probably need to dance around tox by using the wheel, because tox-travis installs various virtualenv (esp. virtualenv<13 on Python 3.2), and those virtualenv may install very old setuptools into the venv.

[jayvdb]

I've found two solutions which I believe will work with any version of setuptools.
pypa/packaging#72 (comment)
I'm still looking for downsides, but havent found any yet.

I'll be working on that over the w/e, as that reduces the chance that tox-travis users will have their builds broken by this enhancement which most users will probably not use in the near future.

[ryanhiebert]

#24 was merged, so this is no longer appropriate to merge, as they were targeting the same result.