Fix Heroku builds by locking python-poetry-buildpack version

[arsalansufi]

Overview

Heroku builds recently started failing. On the left is a successful build, and on the right is a failed build:

Recent updates to the python-poetry-buildpack seem to be responsible. Simplest fix for now is to lock to a specific version of the buildpack by specifying a commit hash. Others have also used this technique to bypass issues with the buildpack, as noted in this comment. Through trial-and-error, I've found the latest commit that still works for us.

Note that I'm not sure how the app.json file and Heroku console interact. It's possible that, even after merging this, I'll have to manually update the buildpacks section of the console.

Testing

Manually updated the buildpacks section of the console for staging and deployed successfully

[jonahkagan]

Seems fine for now.

Did you try updating to a more recent Poetry version?

Is it worth reporting an issue with the buildpack repo?

[arsalansufi]

@jonahkagan I timeboxed an attempt to upgrade Poetry and couldn't quite get things working. I updated the POETRY_VERSION Heroku config var to the latest (1.7.1) and ran into the following error when building in Heroku:

Dependency walk failed at consistent-sampler (*) @ git+https://github.com/votingworks/consistent_sampler.git

I updated my local Poetry and tried re-running poetry install in the hopes that that would modify the poetry.lock or pyproject.toml but didn't see any changes.

While I was at it, I did notice a discrepancy between the Poetry version installed for local dev and the one installed by Heroku. I accordingly updated local dev to match Heroku: aa76581.

Re reporting an issue with the buildpack repo, that makes sense to me. Can do.

Will also open a Vx issue for updating Poetry and removing the stopgap fix introduced by this PR, which will likely be rendered unnecessary by updating Poetry.

[arsalansufi]

Actually, on second thought, I decided not to open an issue with the buildpack repo. The issue makes sense to me. The buildpack recently added a poetry self add command (link), which isn't supported by our outdated version of Poetry. There was even a recent correction to that line to support older versions of Poetry, but our version is particularly outdated. I think that upgrading Poetry is the right fix.

[jonahkagan]

Thanks for diving deeper. That all makes sense to me