array outputs not understood by matrix when nested inside object

[CamJN]

Describe the bug
I cannot use an output as part of a matrix if the matrix is an object.

To Reproduce
Steps to reproduce the behavior:

1. Create the following workflow file:
2. Run it
3. observe that the array is inlined as the word Array in use-matrix-type-1 and the array is inlined as plain string in use-matrix-type-2.

name: Debug

defaults:
  run:
    shell: bash

on:
  workflow_dispatch

jobs:

  define-matrix:
    runs-on: ubuntu-latest
    outputs:
      rpms: ${{ steps.distros.outputs.rpms }}
      debs: ${{ steps.distros.outputs.debs }}
    steps:
      - id: distros
        run: |
          echo 'debs=["focal", "jammy", "noble", "plucky", "bullseye", "bookworm"]' >> "$GITHUB_OUTPUT"
          echo 'rpms=["el8", "el9"]' >> "$GITHUB_OUTPUT"
          cat "$GITHUB_OUTPUT"

  debug:
    runs-on: ubuntu-latest
    needs: [ define-matrix ]
    steps:
      - run: |
          echo '${{ needs.define-matrix.outputs.debs }}'
          echo '${{ needs.define-matrix.outputs.rpms }}'
          echo '${{ fromJSON(needs.define-matrix.outputs.debs) }}'
          echo '${{ fromJSON(needs.define-matrix.outputs.rpms) }}'

  use-matrix-type-1:
    runs-on: ${{ matrix.arch.runner }}
    needs: [ define-matrix ]
    strategy:
      matrix:
        arch:
          - name: x86_64
            runner: ubuntu-24.04
          - name: aarch64
            runner: ubuntu-24.04-arm
        component:
          - name: rhel
            distro: ${{ fromJSON(needs.define-matrix.outputs.rpms) }}
          - name: debian
            distro: ${{ fromJSON(needs.define-matrix.outputs.debs) }}
    steps:
      - run: echo ${{ matrix.component.name }} ${{ matrix.component.distro }}

  use-matrix-type-2:
    runs-on: ${{ matrix.arch.runner }}
    needs: [ define-matrix ]
    strategy:
      matrix:
        arch:
          - name: x86_64
            runner: ubuntu-24.04
          - name: aarch64
            runner: ubuntu-24.04-arm
        component:
          - name: rhel
            distro: ${{ needs.define-matrix.outputs.rpms }}
          - name: debian
            distro: ${{ needs.define-matrix.outputs.debs }}
    steps:
      - run: echo ${{ matrix.component.name }} ${{ matrix.component.distro }}

Expected behavior
I expect the array to be inlined as an array so that the matrix runs the job for each distro in the array.

Runner Version and Platform

Current runner version: '2.323.0'
Operating System
  Ubuntu
  24.04.2
  LTS
Runner Image
  Image: ubuntu-24.04
  Version: 20250406.1.0
  Included Software: https://github.com/actions/runner-images/blob/ubuntu24/20250406.1/images/ubuntu/Ubuntu2404-Readme.md
  Image Release: https://github.com/actions/runner-images/releases/tag/ubuntu24%2F20250406.1

What's not working?

The array is inlined as the word Array in the use-matrix-type-1 job and the array is inlined as plain string in the use-matrix-type-2 job.

Job Log Output

2025-04-07T20:08:00.3009028Z Current runner version: '2.323.0'
2025-04-07T20:08:00.3033356Z ##[group]Operating System
2025-04-07T20:08:00.3034143Z Ubuntu
2025-04-07T20:08:00.3034703Z 24.04.2
2025-04-07T20:08:00.3035226Z LTS
2025-04-07T20:08:00.3035704Z ##[endgroup]
2025-04-07T20:08:00.3036451Z ##[group]Runner Image
2025-04-07T20:08:00.3037097Z Image: ubuntu-24.04
2025-04-07T20:08:00.3037626Z Version: 20250406.1.0
2025-04-07T20:08:00.3038693Z Included Software: https://github.com/actions/runner-images/blob/ubuntu24/20250406.1/images/ubuntu/Ubuntu2404-Readme.md
2025-04-07T20:08:00.3040098Z Image Release: https://github.com/actions/runner-images/releases/tag/ubuntu24%2F20250406.1
2025-04-07T20:08:00.3041011Z ##[endgroup]
2025-04-07T20:08:00.3041608Z ##[group]Runner Image Provisioner
2025-04-07T20:08:00.3042216Z 2.0.422.1
2025-04-07T20:08:00.3042666Z ##[endgroup]
2025-04-07T20:08:00.3045079Z ##[group]GITHUB_TOKEN Permissions
2025-04-07T20:08:00.3047678Z Actions: write
2025-04-07T20:08:00.3048515Z Attestations: write
2025-04-07T20:08:00.3049117Z Checks: write
2025-04-07T20:08:00.3049712Z Contents: write
2025-04-07T20:08:00.3050260Z Deployments: write
2025-04-07T20:08:00.3050817Z Discussions: write
2025-04-07T20:08:00.3051322Z Issues: write
2025-04-07T20:08:00.3051834Z Metadata: read
2025-04-07T20:08:00.3052365Z Models: read
2025-04-07T20:08:00.3052906Z Packages: write
2025-04-07T20:08:00.3053715Z Pages: write
2025-04-07T20:08:00.3054254Z PullRequests: write
2025-04-07T20:08:00.3054857Z RepositoryProjects: write
2025-04-07T20:08:00.3055436Z SecurityEvents: write
2025-04-07T20:08:00.3056075Z Statuses: write
2025-04-07T20:08:00.3057012Z ##[endgroup]
2025-04-07T20:08:00.3060056Z Secret source: Actions
2025-04-07T20:08:00.3061211Z Prepare workflow directory
2025-04-07T20:08:00.3433340Z Prepare all required actions
2025-04-07T20:08:00.3484450Z Complete job name: define-matrix
2025-04-07T20:08:00.4271205Z ##[group]Run echo 'debs=["focal", "jammy", "noble", "plucky", "bullseye", "bookworm"]' >> "$GITHUB_OUTPUT"
2025-04-07T20:08:00.4272398Z �[36;1mecho 'debs=["focal", "jammy", "noble", "plucky", "bullseye", "bookworm"]' >> "$GITHUB_OUTPUT"�[0m
2025-04-07T20:08:00.4273296Z �[36;1mecho 'rpms=["el8", "el9"]' >> "$GITHUB_OUTPUT"�[0m
2025-04-07T20:08:00.4273886Z �[36;1mcat "$GITHUB_OUTPUT"�[0m
2025-04-07T20:08:00.4627343Z shell: /usr/bin/bash --noprofile --norc -e -o pipefail {0}
2025-04-07T20:08:00.4628390Z ##[endgroup]
2025-04-07T20:08:00.4879122Z debs=["focal", "jammy", "noble", "plucky", "bullseye", "bookworm"]
2025-04-07T20:08:00.4879872Z rpms=["el8", "el9"]
2025-04-07T20:08:00.4990212Z Evaluate and set job outputs
2025-04-07T20:08:00.5024999Z Set output 'rpms'
2025-04-07T20:08:00.5027468Z Set output 'debs'
2025-04-07T20:08:00.5028452Z Cleaning up orphan processes

Runner and Worker's Diagnostic Logs

I'm not sure if this info would be helpful.

[CamJN]

I should add that I use this approach successfully when I'm not trying to include an array into the matrix as part of an object: https://github.com/phusion/passenger_apt_automation/actions/runs/14203546100