Support PEP 517 and 518

[cjolowicz]

No description provided.

[cjolowicz]

CI failed with this error:

$ bundle exec hatchet ci:setup
/home/travis/build/cjolowicz/heroku-buildpack-python/vendor/bundle/ruby/2.4.0/gems/heroku_hatchet-4.0.6/etc/ci_setup.rb:10:
in `fetch': key not found: "HEROKU_API_USER" (KeyError)

It appears we first need to configure Travis for Heroku access: #2

[cjolowicz]

CI failed because some tests didn't pass:

testPoetry

pip refuses to perform an editable install for a pyproject.toml-based project.

testPoetry
ASSERT:Captured exit code - expected:<0> but was:<1>
-----> Installing python-3.6.8
-----> Installing pip
-----> Installing SQLite3
-----> Installing requirements with pip
       ERROR: File "setup.py" not found. Directory cannot be installed in editable mode: /tmp/testJLs6T
       (A "pyproject.toml" file was found, but editable mode currently requires a setup.py based build.)

testPoetryLock

Same as above.

testPoetryLock
ASSERT:Captured exit code - expected:<0> but was:<1>
-----> Installing python-3.6.8
-----> Installing pip
-----> Installing SQLite3
-----> Installing requirements with pip
       ERROR: File "setup.py" not found. Directory cannot be installed in editable mode: /tmp/testvjOhS
       (A "pyproject.toml" file was found, but editable mode currently requires a setup.py based build.)

testSmartRequirements

This is a regression, possibly caused by the pip upgrade. Apparently obsolete requirements are not uninstalled correctly.

testSmartRequirements
ASSERT:Expected </tmp/shunit.nlRHuC/tmp/output.nU2q/stdout> to contain <Uninstalling requests>
-----> Installing requirements with pip
       Collecting psycopg2 (from -r /tmp/testHoJ9o/requirements.txt (line 1))
         Downloading https://files.pythonhosted.org/packages/5c/1c/6997288da181277a0c29bc39a5f9143ff20b8c99f2a7d059cfb55163e165/psycopg2-2.8.3.tar.gz (377kB)
       Building wheels for collected packages: psycopg2
         Building wheel for psycopg2 (setup.py): started
         Building wheel for psycopg2 (setup.py): finished with status 'done'
         Created wheel for psycopg2: filename=psycopg2-2.8.3-cp36-cp36m-linux_x86_64.whl size=445840 sha256=09486d748c43fc8bc6af2f363fc274314c5faf9adfdbf4a172f4b5cff00650d7
         Stored in directory: /tmp/pip-ephem-wheel-cache-pbj7gvfl/wheels/48/06/67/475967017d99b988421b87bf7ee5fad0dad789dc349561786b
       Successfully built psycopg2
       Installing collected packages: psycopg2
       Successfully installed psycopg2-2.8.3

[cjolowicz]

Editable install and pyproject.toml

Related issues and PRs:

PR	Issue
pypa/pip#6331	pypa/pip#6314
pypa/pip#6370	pypa/pip#6375
-	python-poetry/poetry#826