Adds support for:
* CPython 2.7.18, 3.5.9, 3.7.7 and 3.8.3
* PyPy 2.7 and 3.6, version 7.3.1
The binaries will need generating and uploading before CI will pass.
Note: Whilst the build script for CPython 3.8.3 did already exist in the
repository, it appears to have been accidentally created in #920, which
predated the existence of that version of Python - so the binaries do
not exist on S3.
The Heroku-18 Docker image tag has also been unpinned, since the new
libssl version is now available at runtime in all environments, so we
don't need to force building against the older version of the headers.
Fixes W-7582174.
The compile-time cryptography step that used to use the libffi archives
on S3 was removed in 2018:
https://github.com/heroku/heroku-buildpack-python/commit/c373e80c1285260e5adcbc855f54bbeb6999005c
...since the `cryptography` Python package now ships wheels.
The script is also incorrect, since similar to #964 it only skips builds
for Heroku-16, whereas all stacks since Cedar-14 include libffi-dev in
the build image, so don't need it built/uploaded for later vendoring.
Refs W-7485877.
The `libmemcached` package is available in the base stack image for all
stacks newer than `cedar-14`, so at buildpack compile time the vendor
step is skipped for those stacks:
https://github.com/heroku/heroku-buildpack-python/blob/106f2997fa124852a2a35ee8bfa604ad20c47988/bin/steps/pylibmc#L12-L15
As such, it is not necessary to run the libmemcached bob-builder formula
on newer stacks. The conditional has been updated so it correctly handles
heroku-18 and also the upcoming heroku-20.
An exit code of 1 has been used, otherwise `bob upload` will build and
then upload a zero byte archive to S3, which will go unused.
(This is in comparison to bob formulas that are nested, where an exit
code of 0 is actually desirable, since it allows skipping steps.)
Refs W-7485877.
Co-authored-by: Joe Kutner <jpkutner@gmail.com>
Denis Cornehl