Add release pipeline GitHub Action

[michaelosthege]

Description

This PR adds a GitHub Action with a release pipeline.

I commented out a few blocks/lines to make the pipeline run on this PR. Which it doesn't, because the GitHub action does not activate before it's on master.

Before merging, the TODO lines (except the tests) MUST be addressed.

Also, a GitHub Action Secret must be created in the Settings of the GitHub repository:

The pipeline currently does not run tests. For now, we must not create release tags if the pipeline failed on master.

TODO

• switch the on condition (will skip the pipeline from the last PR commit before merging, but run it when the release is created)
• remove the export GITHUB_REF which is just there to simulate the creation of the release tag
• add the PYPI_TOKEN secret as described above
• enable the twine upload line
• switch the pip install pymc3 line to the one that uses the released version

References

• https://github.com/pymc-devs/pymc3/wiki/PyMC3-Release-Checklist
• https://github.com/michaelosthege/pyrff/blob/master/.github/workflows/release.yml

[michaelosthege]

The steps from the pipeline can be tested in a Docker container:

git clone https://github.com/michaelosthege/pymc3
cd pymc3
git checkout add-action
git pull
docker run --rm -it -v $(pwd):/pymc3 --workdir=/pymc3 python:3.7 bash

[AlexAndorra]

This looks really helpful, thanks a lot @michaelosthege ! I think the Release Checklist should be updated accordingly.

[ericmjl]

@michaelosthege sorry for getting back so late on this! I wanted to raise a question - if we want tests to pass before deploy, and for it to deploy only on master, could we get this done instead on Travis? This would make sense, given that Travis is the CI service that is running tests for us.

I finally read the Travis docs on how to make it happen, and it looks very similar to how you've defined it using GitHub actions. This weekend I've made some time to dry-run a python package deploy, and can report back. (Sorry for the delay again, I was writing a long notebook on probability, for my own learning, all of the week.)

[michaelosthege]

@ericmjl No, it doesn't work on travis (took me 4 hours to learn this when trying for pyrff).
The reason is because Travis has no way to provide secrets to a pipeline running on a non-master branch. Tag-triggered pipelines on Travis don't run on master, so they don't get the secrets.

I think it's fine that the pipeline doesn't run the tests. We just don't create a Release if the master pipeline is red.

Also, we have more pressing worries, like building docs.