Error when using macOS-15 in runs-on matrix configuration

[Drewniok]

Description

Description

I am encountering an issue (while creating this PR), specifically when configuring a GitHub Actions workflow matrix that includes macOS-15. Adding macOS-15 to the matrix causes the workflow to fail in evaluating the runs-on property, resulting in the following error:

Error when evaluating 'runs-on' for job 'build_and_test'. .github/workflows/macos.yml (Line: 40, Col: 14): Unexpected value ''

This issue does not occur when macOS-15 is excluded from the matrix.

Workflow Configuration

Here is the relevant snippet (whole workflow can be found here) of the GitHub Actions workflow:

jobs:
  build_and_test:
    strategy:
      matrix:
        os: [macos-13, macos-14, macos-15]
        compiler: [g++-12, g++-13, g++-14, clang++]
        include:
          - os: macos-13
            architecture: x64
          - os: macos-14
            architecture: arm64
          - os: macos-15
            architecture: arm64
          - compiler: clang++
            ccompiler: clang
          - compiler: g++-12
            ccompiler: gcc-12
          - compiler: g++-13
            ccompiler: gcc-13
          - compiler: g++-14
            ccompiler: gcc-14

        exclude:
          - os: macos-13
            compiler: g++-13
          - os: macos-14
            compiler: g++-12
          - os: macos-14
            compiler: g++-13
          - os: macos-15
            compiler: g++-12
          - os: macos-15
            compiler: g++-13

    name: 🍎 ${{ matrix.os }} with ${{ matrix.compiler }}
    runs-on: ${{ matrix.os }}

Platforms affected

• Azure DevOps
• GitHub Actions - Standard Runners
• GitHub Actions - Larger Runners

Runner images affected

• Ubuntu 20.04
• Ubuntu 22.04
• Ubuntu 24.04
• macOS 12
• macOS 13
• macOS 13 Arm64
• macOS 14
• macOS 14 Arm64
• macOS 15
• macOS 15 Arm64
• Windows Server 2019
• Windows Server 2022
• Windows Server 2025

Image version and build link

https://github.com/cda-tum/fiction/actions/runs/12647205220/workflow

Is it regression?

https://github.com/cda-tum/fiction/actions/runs/12261209867

Expected behavior

The workflow should execute with macOS-15 in the matrix, just like it does with macOS-13 and macOS-14.

Actual behavior

When macOS-15 is included in the matrix, the workflow fails with the error message mentioned above. Removing macOS-15 resolves the issue.

Repro steps

1. Add macOS-15 to the os matrix in the workflow configuration.
2. Run the workflow.
3. Observe the error during evaluation of the runs-on property.

[susmitamane]

Hi @Drewniok

We will look into the issue and keep you posted with updates.

Thank You.