[v3.0] Add newer Python 3 versions to build matrix

[adamantike]

For the 3.0 branch, add newer Python versions to the build matrix, up
to Python 3.7.

This is motivated by #1100, which backported a fix for the 3.0 branch
to work with Python 3.7.

[coveralls]

Coverage remained the same at 91.757% when pulling ad98029 on adamantike:3.0-add-support-for-newer-python into 4249443 on celery:3.0.

[coveralls]

Coverage decreased (-10.4%) to 81.32% when pulling 74dc1ed on adamantike:3.0-add-support-for-newer-python into 4249443 on celery:3.0.

[adamantike]

@auvipy ping for awareness! With these changes to the 3.0 branch, only the pypy build is currently failing in Travis, and everything from AppVeyor. Let me know if it makes sense to keep working on them, before putting more effort into it.

Hopefully, this could allow us to have another 3.x release, compatible with newer Python versions :)

[auvipy]

drop EOL py versions

[adamantike]

I would gladly remove those versions! As it would be a breaking change for those Python versions, I wasn't sure of the approach you take on this project, as this commit will be tagged as minor/patch within the 3.0 branch. If that's OK, I will proceed with those changes.

[auvipy]

It's normal to drop the python version reaching EOL. we are not supposed to support celery 3.x as well but doing so for the sake of easier migration to 4.x versions.

[adamantike]

AppVeyor is now fixed by using almost the same configuration as master. The only pending one is the pypy environment in Travis, which of course, passes when running tests locally.

[auvipy]

can you update pypy2.7 to 7.2?

[adamantike]

I don't see pypy2.7-7.2 still supported by Travis, considering its nightly builder, and its documentation. That's why I'm using the same PyPy versions we test in master.

[auvipy]

I added it on celery master, check it

[adamantike]

I can add it to check if it works, but that environment didn't run for your PR: https://travis-ci.org/celery/celery/builds/601834152, and I don't see it running afterwards because it's in the lint stage, which is only executed if the previous stage is successful, while has been failing consistently in master celery.

[adamantike]

I tested both pypy2.7-7.2 and pypy2.7-7.2.0, and Travis fails with:

Downloading archive: https://storage.googleapis.com/travis-ci-language-archives/python/binaries/ubuntu/16.04/x86_64/pypy2.7-7.2.tar.bz2
0.13s$ curl -sSf -o pypy2.7-7.2.tar.bz2 ${archive_url}
curl: (22) The requested URL returned error: 404 Not Found
Unable to download pypy2.7-7.2 archive. The archive may not exist. Please consider a different version.

(from https://travis-ci.org/celery/kombu/jobs/602304400)

[auvipy]

OK stick with 7.1.x

[adamantike]

So, I still don't know why the pypy environment fails in Travis, where this simple assertion about installed codecs fails:

import codecs
codecs.lookup('ascii')

My guess is that the PyPy installation provided by Travis is missing something, but I don't think it should block this PR from being merged.

This pull request is now ready for review. After this one, I will check if migrating the test suite to PyTest makes any difference to fix that breaking environment.

[adamantike]

@auvipy, let me know if is there anything else I should add to this PR, to be merged.

[auvipy]

OK. moving to pytest makes sense.