runs-on does not support ${{ wrapped multiline expression }}: workflow hanging at startup

[XuehaiPan]

Why are you starting this discussion?

Bug

What GitHub Actions topic or product is this about?

Workflow Configuration

Discussion Details

As the following configuration shows, I have a very complex workflow matrix strategy while also having some special cases. So I use a ${{ expr }} to determine the runner image. Since the expression is too long, I wrap it to:

jobs:
  build-wheels:
    if: |
      github.repository_owner == 'metaopt' &&
      (github.event_name != 'push' || startsWith(github.ref, 'refs/tags/')) &&
      (github.event_name != 'pull_request' || !github.event.pull_request.draft)
    # https://docs.github.com/en/actions/reference/runners/github-hosted-runners
    runs-on: |
      ${{
        (matrix.archs == 'ARM64' && 'windows-11-arm') ||
        (matrix.archs == 'aarch64' && 'ubuntu-24.04-arm') ||
        matrix.runner
      }}

No error is raised for the configuration syntax, but the workflow hangs at startup without displaying any logs.

The full configuration: https://github.com/metaopt/optree/blob/main/.github/workflows/build.yml#L108

jobs:
  build-wheels:
    name: Build wheels for Python ${{ matrix.python-version }} on ${{ (matrix.archs == 'ARM64' && 'windows-11-arm') || (matrix.archs == 'aarch64' && 'ubuntu-24.04-arm') || matrix.runner }} (${{ matrix.archs }})
    if: |
      github.repository_owner == 'metaopt' &&
      (github.event_name != 'push' || startsWith(github.ref, 'refs/tags/')) &&
      (github.event_name != 'pull_request' || !github.event.pull_request.draft)
    # https://docs.github.com/en/actions/reference/runners/github-hosted-runners
    runs-on: ${{ (matrix.archs == 'ARM64' && 'windows-11-arm') || (matrix.archs == 'aarch64' && 'ubuntu-24.04-arm') || matrix.runner }}
    strategy:
      matrix:
        runner: [ubuntu-latest, macos-latest, windows-latest]
        python-version:
          - "3.9"
          - "3.10"
          - "3.11"
          - "3.12"
          - "3.13"
          - "3.13t"
          - "3.14"
          - "3.14t"
          - "pypy-3.10"
          - "pypy-3.11"
        archs:
          # Generic
          - "auto64"
          - "auto32"
          # Linux
          - "aarch64"
          - "ppc64le"
          - "s390x"
          # Windows
          - "ARM64"
        exclude:
          - runner: ubuntu-latest
            python-version: "pypy-3.10"
            archs: "ppc64le"
          - runner: ubuntu-latest
            python-version: "pypy-3.11"
            archs: "ppc64le"
          - runner: ubuntu-latest
            python-version: "pypy-3.10"
            archs: "s390x"
          - runner: ubuntu-latest
            python-version: "pypy-3.11"
            archs: "s390x"
          - runner: windows-latest
            python-version: "3.9"
            archs: "ARM64"
          - runner: windows-latest
            python-version: "3.10"
            archs: "ARM64"
          - runner: windows-latest
            python-version: "pypy-3.10"
            archs: "ARM64"
          - runner: windows-latest
            python-version: "pypy-3.11"
            archs: "ARM64"
          - python-version: "pypy-3.10"
            archs: "auto32"
          - python-version: "pypy-3.11"
            archs: "auto32"
          # Exclude archs of other platforms
          - runner: ubuntu-latest
            archs: "ARM64"
          - runner: macos-latest
            archs: "auto32"
          - runner: macos-latest
            archs: "aarch64"
          - runner: macos-latest
            archs: "ppc64le"
          - runner: macos-latest
            archs: "s390x"
          - runner: macos-latest
            archs: "ARM64"
          - runner: windows-latest
            archs: "aarch64"
          - runner: windows-latest
            archs: "ppc64le"
          - runner: windows-latest
            archs: "s390x"
        include:
          - runner: macos-latest
            python-version: "3.13"
            archs: "arm64_iphoneos"
          - runner: macos-latest
            python-version: "3.13"
            archs: "arm64_iphonesimulator"
          - runner: ubuntu-latest
            python-version: "3.13"
            archs: "arm64_v8a"
          - runner: ubuntu-latest
            python-version: "3.12"
            archs: "wasm32"
      fail-fast: false
    timeout-minutes: 180
    steps:
      - ...

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[ChristopherHX]

The solution is a single - after : | e.g. : |- to tell yaml you do not want an additional newline after }}.

e.g.

jobs:
  build-wheels:
    if: |
      github.repository_owner == 'metaopt' &&
      (github.event_name != 'push' || startsWith(github.ref, 'refs/tags/')) &&
      (github.event_name != 'pull_request' || !github.event.pull_request.draft)
    # https://docs.github.com/en/actions/reference/runners/github-hosted-runners
    runs-on: |-
      ${{
        (matrix.archs == 'ARM64' && 'windows-11-arm') ||
        (matrix.archs == 'aarch64' && 'ubuntu-24.04-arm') ||
        matrix.runner
      }}

And everything is fine.

GitHub Actions is probably looking for a runner with label "windows-11-arm\n", "ubuntu-24.04-arm\n" or "${{ matrix.runner}}\n", given it cannot find anyone online it expects you to start a self-hosted runner. I assume it could be really hard to actually get a runner with a newline in the label to get registred.

Learning how YAML works in detail, might be good knowledge while writing workflows

[XuehaiPan]

GitHub Actions is probably looking for a runner with label "windows-11-arm\n", "ubuntu-24.04-arm\n" or "${{ matrix.runner}}\n", given it cannot find anyone online it expects you to start a self-hosted runner.

Thanks for the hint! I changed to the following and everything works fine:

jobs:
  build-wheels:
    name: >-
      Build wheels for Python ${{ matrix.python-version }} on
      ${{
        (matrix.archs == 'ARM64' && 'windows-11-arm') ||
        (matrix.archs == 'aarch64' && 'ubuntu-24.04-arm') ||
        matrix.runner
      }}
      (${{ matrix.archs }})
    if: |
      github.repository_owner == 'metaopt' &&
      (github.event_name != 'push' || startsWith(github.ref, 'refs/tags/')) &&
      (github.event_name != 'pull_request' || !github.event.pull_request.draft)
    # https://docs.github.com/en/actions/reference/runners/github-hosted-runners
    runs-on: >-
      ${{
        (matrix.archs == 'ARM64' && 'windows-11-arm') ||
        (matrix.archs == 'aarch64' && 'ubuntu-24.04-arm') ||
        matrix.runner
      }}

Reference for YAML multiline: https://yaml-multiline.info/