feat(github): add disko comparison workflow

Author: georgiyord

.github/workflows/reusable-compare-disko.yml

@@ -0,0 +1,61 @@
+name: 'Compare Disko NixOS configs'
+
+on:
+  # Allow this workflow to be reused by other workflows:
+  workflow_call:
+    inputs:
+      runner:
+        description: 'JSON-encoded list of runner labels'
+        default: '["self-hosted"]'
+        required: false
+        type: string
+    secrets:
+      CACHIX_AUTH_TOKEN:
+        description: 'Cachix auth token'
+        required: true
+
+jobs:
+  post-initial-comment:
+    runs-on: ${{ fromJSON(inputs.runner) }}
+    steps:
+      - name: 'Post initial disko status comment'
+        uses: marocchino/[email protected]
+        with:
+          recreate: true
+          message: |
+            Thanks for your Pull Request!
+
+            This comment will be updated automatically with the status of disko on each machine.
+  compare-disko-configs:
+    runs-on: ${{ fromJSON(inputs.runner) }}
+    name: 'Compare disko configs on machines'
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Install Nix
+        uses: metacraft-labs/nixos-modules/.github/install-nix@main
+        with:
+          cachix-cache: ${{ vars.CACHIX_CACHE }}
+          cachix-auth-token: ${{ secrets.CACHIX_AUTH_TOKEN }}
+
+      - name: Compare disko configurations
+        env:
+          CACHIX_CACHE: ${{ vars.CACHIX_CACHE }}
+          CACHIX_AUTH_TOKEN: ${{ secrets.CACHIX_AUTH_TOKEN }}
+          # MCL_BRANCH: ${{ github.repository == 'metacraft-labs/nixos-modules' && github.sha || 'main' }}
+          MCL_BRANCH: ${{ github.repository == 'metacraft-labs/nixos-modules' && github.sha || 'feat/compare-disko' }}
+        run: nix run --accept-flake-config github:metacraft-labs/nixos-modules/${{ env.MCL_BRANCH }}#mcl compare_disko
+
+  create-comment:
+    runs-on: ${{ fromJSON(inputs.runner) }}
+    name: 'Create comment'
+    needs: [post-initial-comment, compare-disko-configs]
+
+    steps:
+      - name: Post Comment
+        uses: marocchino/[email protected]
+        with:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          recreate: true
+          path: comment.md