I got the following error that HOME environment variable is not set.

https://github.com/ruby/ruby/actions/runs/16448587964/job/46487337166

$ git config --global core.autocrlf false
fatal: $HOME not set
Error: Process completed with exit code 128.

So, I added the following hack to set the HOME environment variable.

      # This is a temporary workaround to set HOME env to pass the next step
      # ./.github/actions/setup/directories.
      - name: Set HOME env
        run: |
          echo "HOME: #{HOME}"
          pushd ~
          echo "HOME=$(pwd)" >> $GITHUB_ENV
          popd
        if: ${{ endsWith(matrix.os, 'ppc64le') || endsWith(matrix.os, 's390x') }}

However, it seems the directory by the ~ doesn't exsit.

https://github.com/ruby/ruby/actions/runs/16449252485/job/46489719903?pr=13972

Error: An error occurred trying to start process '/usr/bin/bash' with working directory '/tmp/_actions-runner-working-dir/ruby/ruby/build'. No such file or directory

@Earlopain, I am trying to skip ubuntu-24.04-ppc64le and ubuntu-24.04-s390x cases of the .github/workflows/ubuntu.yml in the matrix in forked repositories, still running the ubuntu-24.04-arm, using your way mentioned at the ruby/prism#3611 (comment).

https://github.com/ruby/ruby/pull/13972/files#diff-6640e8c668a6deeb426558faaa2b0f535d95814c09a05c044a1df27a008dd544

However, it seems all the cases are skipped in the current config file. Could you give me an advice to run the ppc64le/s390x as I intend? Thanks!

As a reference, the document of the matrix is below.

https://docs.github.com/en/actions/how-tos/writing-workflows/choosing-what-your-workflow-does/running-variations-of-jobs-in-a-workflow

Unfortunatly excludes are run before includes so it doesn't work for this setup. But if you rewrite it a bit, it seems to work:

      matrix:
        os: [ ubuntu-22.04, ubuntu-24.04, ubuntu-24.04-arm, ubuntu-24.04-ppc64le, ubuntu-24.04-s390x ]
        test_task: [check]
        configure: ['']
        arch: ['']
        timeout: [40]
        # The ppc64le/s390x runners works only in the registered repositories.
        # They don't work in forked repositories.
        # https://github.com/IBM/actionspz/blob/main/docs/FAQ.md#what-about-forked-repos
        upstream:
          - ${{ github.repository == 'ruby/ruby' }}
        include:
          - test_task: check
            configure: 'cppflags=-DVM_CHECK_MODE'
          - test_task: check
            arch: i686
          - test_task: check
            configure: '--disable-yjit'
          - test_task: check
            configure: '--enable-shared --enable-load-relative'
          - test_task: test-bundler-parallel
            timeout: 50
          - test_task: test-bundled-gems
        exclude:
          - os: ubuntu-24.04-ppc64le
            upstream: false
          - os: ubuntu-24.04-s390x
            upstream: false
      fail-fast: false

I think this is what you are looking for. I tested this in one of my repos and it does what I would expect it to. This is good as long as you only want to run the check task though. Anything more complicated runs into the previously mentioned limitation.

There are more general solutions to this by dynamically creating the test matrix in a previous job, writing that to an output, and then refering to that output in the job that needs the matrix. Basically what is happening here: https://github.com/ruby/actions/blob/master/.github/workflows/ruby_versions.yml. It's a bit more complicated though.