CI Testing Matrix

[mpharrigan]

Problem overview

We depend on openfermion, pytket, and pytket-cirq; which have historically been over-pinned to a particular cirq version. "Overpinned" means that even if it seems to work with a newer (or older!) cirq version, the install_requires still specifies one version. pip has recently (past year) learned to be strict about satisfying requirements. pip will end up in an infinite loop downloading old versions instead of saying which package is causing a version deadlock

As a developer, I can get things to work by installing dependencies myself and then pip install --no-deps openfermion, cirq, pytket, or recirq so pip can't get in my way.

However, one important use case is supporting colab which must have a simple install script; hopefully just pip install recirq (or, specifically, the git url).

Openfermion relaxation

Cirq has been generally stable across the past couple of releases, especially if one were to go through and fix deprecation warnings. Indeed, I have changed openfermion quantumlib/OpenFermion#755 to not pin in install_requires but to use the CI to test against multiple versions of Cirq.

Towards relaxing ReCirq

This PR aims to head towards the same goal. We test against the previous, current, and next version of Cirq. Testing against the next version of Cirq is particularly important when committing code that depends on unreleased Cirq features. The trick is to attempt the full matrix of versions, and lean heavily on pytest.mark.skipif to make sure tests only run under supported configurations.

In particular, we introduce a script to capture the intricacies of the various test configurations: write-ci-requirements.txt. This lets us pin to a particular cirq version during CI testing but not in install_requires, which we change to a lower bound.

This script has several notable features

• translate fixed "relative" versions like current, previous, and next to numeric, pypi ones. Otherwise, the numeric versions from the CI matrix will show up in the job names. We want to set the "required checks" setting on GitHub without having it rely on the current cirq versions, which will change over time
• Hacky pytket logic: don't test the pytket functionality on the next cirq version.

Cirq 0.13

This fixes #224 because pytket and openfermion have compatible versions now.

Cirq 0.14

We'll now be in the regime where we need to fix ReCirq for the next Cirq version before it is released. As such, this PR is based off of #241 .

Per-package testing

This still tests the whole ReCirq repository at once. We can modify write-ci-requirements.py to help simplify a new matrix job that tests each subpackage in isolation. skipif may be a large component to that as well.

[mpharrigan]

rebased off of #241

[dstrain115]

Cool! One step towards a better ecosystem!

[dstrain115]

Should we put a note in the requirements.txt file so that people know to go and update this?

[mpharrigan]

good idea, done

[dstrain115]

Maybe a quick comment here to explain that this is here for CI tests?

[mpharrigan]

added:

    # Set the 'RECIRQ_IGNORE_PYTKET' environment variable to treat PyTket as an optional
    # dependency. We do this for CI testing against the next, pre-release Cirq version.

(in general, users could also set this environment variable if they get themselves into hot water managing the pytket dependency)

[mpharrigan]

I modified the master branch protection rules to use the new test names. I also added the notebook formatting test, which was never a required test