Dynamic Ruby versions matrix on GitHub Actions

ruby.yml

name: Test

on: push

jobs:
  ruby-versions:
    runs-on: ubuntu-latest
    outputs:
      versions: ${{ steps.versions.outputs.value }}
    steps:
      - id: versions
        name: Fetch Ruby versions
        run: |
          versions="$(curl -s 'https://cache.ruby-lang.org/pub/misc/ci_versions/cruby.json' | jq -c)"
          echo "Fetched Ruby versions: ${versions}"
          echo "::set-output name=value::${versions}"

  test:
    name: Test on Ruby ${{ matrix.ruby }}
    needs: ruby-versions
    runs-on: ubuntu-latest
    strategy:
      fail-fast: false
      matrix:
        ruby: ${{ fromJson(needs.ruby-versions.outputs.versions) }}
    steps:
      - uses: actions/checkout@v3
      - uses: ruby/setup-ruby@v1
        with:
          ruby-version: ${{ matrix.ruby }}
          bundler-cache: true
      - run: bundle exec rake

See https://cache.ruby-lang.org/pub/misc/ci_versions/ for other versions (e.g. jruby)

An example to add outdated versions to the matrix:

versions=$(curl -s 'https://cache.ruby-lang.org/pub/misc/ci_versions/all.json' | jq -c '. |= . + ["2.6", "2.5", "2.4"]')

See also:
https://github.com/ruby/net-pop/blob/1f06e08cde37e1c20153ca91da2890adeec0e2b3/.github/workflows/test.yml#L13

See https://github.com/ybiquitous/dynamic-ruby-versions-action