name: "Flake checks"
on:
  pull_request:
  push:
    branches:
      - main
jobs:

  flake-checks:
    runs-on: ubuntu-latest
    outputs:
      matrix: ${{ steps.set-matrix.outputs.matrix }}
    steps:
      - uses: actions/checkout@v2.4.0
        with:
          # Nix Flakes doesn't work on shallow clones
          fetch-depth: 0
      - uses: cachix/install-nix-action@v16
        with:
          nix_path: nixpkgs=channel:nixos-unstable
      - id: set-matrix
        run: |
          set -euo pipefail

          matrix="$(nix flake show --json | jq '.checks."x86_64-linux" | keys' | jq -rcM '{attr: ., os: ["ubuntu-latest", "macos-latest"]}')"
          echo "::set-output name=matrix::$matrix"

  builds:
    needs: flake-checks
    runs-on: ${{ matrix.os }}
    strategy:
      matrix: ${{fromJSON(needs.flake-checks.outputs.matrix)}}
    steps:
      - uses: actions/checkout@v2.4.0
        with:
          # Nix Flakes doesn't work on shallow clones
          fetch-depth: 0
      - uses: cachix/install-nix-action@v16
        with:
          nix_path: nixpkgs=channel:nixos-unstable
      - run: |
          set -euo pipefail

          system=$(nix-instantiate --eval --expr builtins.currentSystem | jq -r)
          nix build -L .#checks.$system.${{ matrix.attr }}