Allow CircleCI caches to be manually cleared

[gsmendoza]

Goal

I would like to insert a UI environment variable to our CircleCI cache keys so that we can manually clear them if needed.

Background

We recently have a situation where the Ruby version in the install_solidus cache key doesn't match the Ruby version of the Rails app that was cached. As a result, the mismatch is causing the following error in CI:

Your Ruby version is 2.7.7, but your Gemfile specified 2.7.6

For examples, see:

• https://app.circleci.com/pipelines/github/solidusio/solidus/3838/workflows/2b5f5731-1c8c-4589-bfc0-6206156cd364/jobs/34317?invite=true#step-108-130
• https://app.circleci.com/pipelines/github/nebulab/solidus/625/workflows/effbd9a1-984d-44ca-bfc1-681de35647ed/jobs/7598?invite=true#step-108-128

Proposed implementation

Basing from https://support.circleci.com/hc/en-us/articles/115015426888-Clear-Project-Dependency-Cache, we can insert a UI environment variable to our two cache keys in our CircleCI config:

• solidus-gems-v3-{{ .Environment.CACHE_VERSION }}-{{checksum ".ruby-version"}}-{{ .Branch }}-{{ checksum "Gemfile.lock" }}
• solidus-installer-v5-{{ .Environment.CACHE_VERSION }}-{{ checksum "/tmp/.tool-versions" }}

We'll keep the existing cache version keys (v3 and v5) in the cache keys so that we'll still have the ability to reset the cache via source code change.

Prerequisites

To be safe, we need to seed the CACHE_VERSION environment variable in CircleCI before merging the PR to master.

Post-merge changes

Once merged to master, we'll need to backport the change to older versions of Solidus.

Additional references

• https://circleci.com/docs/set-environment-variable/#set-an-environment-variable-in-a-project

[waiting-for-dev]

I like the idea, @gsmendoza!

Once merged to master, we'll need to

• Seed the CACHE_VERSION environment variable in CircleCI.

We probably need to do that BEFORE merging to master, to avoid the environment variable not being found.

[gsmendoza]

Yep, I agree. I updated the description above 👍