Fixing OutputWriter._iter_lines for pip 8.1.1 or below

[Lucas-C]

Contributor checklist

• Provided the tests for the changes:
  An existing test ensures this does not introduces any regression: https://github.com/jazzband/pip-tools/blob/master/tests/test_writer.py
• Added the changes to CHANGELOG.md
  I don't think this is needed as it is a fix.
• Requested (or received) a review from another contributor
  Nope. Anyone please ? :)

[vphilippon]

Could yo add a test in tests/test_writer.py:
Similar to test_format_requirement_environment_marker, but with a package such as test_foo, and the output being test-foo and the marker is kept.

You can skip the CHANGELOG entry.

[Lucas-C]

I'm totally willing to add a test, but I don't understand what you want to test here ?

My change is in OutputWriter._iter_lines while you asked me to add a test for OutputWriter._format_requirement which is not affected by my changes (marker=None is going to be passed as an argument).

Also this aims to fix a compatibility issue with pip 8.1.1 or below, so maybe the best way to test it would be to add a pip==8.1.1 testenv in https://github.com/jazzband/pip-tools/blob/master/tox.ini#L7 ?

[vphilippon]

You're right, I was under the impression that the formatting was changed, but it's actually the value passed that might be different. That would be a different test.

Adding a test suite in tox using pip 8.1.1 seems reasonable to me, as this version (while having a more recent bugfix version) seems to still be common in the wild.
You can go ahead and add a test environment with pip 8.1.1.

Also, sorry for the delay, life happened. Thank you for your time!

[Lucas-C]

I added a test tox env,
but I'm not 100% sure I got it right :)

[vphilippon]

@Lucas-C You also have to add the new pip 8.1.1 tox environment in .appveyor.yml, for each python version already listed. That's for the Windows tests.
We're almost there, pretty sure we'll be done after that.
Thanks again.

[Lucas-C]

No problem: done !

[vphilippon]

Thanks for your contribution!

[Lucas-C]

Thanks for your help :)