name: Example

on:
  workflow_dispatch:

jobs:
  eval:
    runs-on: ubuntu-latest

    outputs:
      matrix: ${{ steps.generate.outputs.matrix }}

    steps:
      - uses: actions/checkout@v4

      - name: install nix
        uses: nixbuild/nix-quick-install-action@v26

      - name: generate matrix
        id: generate
        run: |
          set -Eeu
          echo "matrix=$(nix eval --show-trace --json .#githubWorkflow.matrix)" >> "$GITHUB_OUTPUT"

  build:
    needs: eval

    strategy:
      matrix: ${{ fromJSON(needs.eval.outputs.matrix) }}

    runs-on: ${{ matrix.os }}

    name: build (${{matrix.attr}})

    steps:
      - uses: actions/checkout@v4

      - name: setup qemu
        if: matrix.arch == 'aarch64'
        run: |
          sudo apt update -y
          sudo apt install -y qemu-user-static

      - name: install nix
        if: matrix.arch != 'aarch64'
        uses: nixbuild/nix-quick-install-action@v26

      - name: install nix (with aarch64)
        if: matrix.arch == 'aarch64'
        uses: nixbuild/nix-quick-install-action@v26
        with:
          nix_conf: "extra-platforms = aarch64-linux arm-linux"

      - name: build ${{ matrix.attr }}
        run: nix build -L --fallback .#${{ matrix.attr }}