Set up some CI

.github/workflows/deploy.yml

@@ -12,6 +12,62 @@ on:
     - reopened
     - labeled
 jobs:
+  test:
+    runs-on: ubuntu-latest
+    name: Check
+    steps:
+    - uses: actions/checkout@v2.3.4
+    - uses: cachix/install-nix-action@v17
+      with:
+        extra_nix_config: |
+          # save space on disk and in cache
+          auto-optimise-store = true
+          # keep all store paths necessary to build the outputs
+          keep-outputs = true
+          keep-derivations = true
+          # Enable flakes
+          experimental-features = nix-command flakes
+    - uses: actions/cache@v2
+      with:
+        key: nki-nix-${{ github.sha }}
+        restore-keys: |
+          nki-nix-
+        path: |
+          nix_store_dir
+          nix_store_db.sqlite
+    - name: restore cached nix store
+      run: |
+        if [ -e nix_store_db.sqlite ]; then
+          sudo systemctl stop nix-daemon
+          # put cached store paths back in their proper locations
+          sudo rm -rf /nix/store /nix/var/nix/db/db.sqlite
+          sudo mv nix_store_dir /nix/store
+          sudo cp nix_store_db.sqlite /nix/var/nix/db/db.sqlite
+          # fix store permissions
+          sudo chmod 1775 /nix/store
+          sudo chown root:nixbld /nix/store
+          sudo chmod 0644 /nix/var/nix/db/db.sqlite
+          sudo chown -R root:root /nix/store /nix/var/nix/db/db.sqlite
+          sudo systemctl start nix-daemon
+        fi
+    - name: Run format check
+      run: |
+        nix fmt
+        if [ -z "$(git status --untracked-files=no --porcelain)" ]; then 
+          echo "Formatted, clean"
+        else
+          echo "The following files are unformatted:"
+          git status
+          false
+        fi
+    - name: prepare nix store for caching
+      run: |
+        # delete old stuff not relevant to this build
+        nix store gc
+        sudo systemctl stop nix-daemon
+        # move store to a place where the cache action can read it
+        sudo mv /nix/store nix_store_dir
+        sudo mv /nix/var/nix/db/db.sqlite nix_store_db.sqlite
   deploy:
     if: "github.event_name == 'push' || contains(github.event.pull_request.labels.*.name, 'Deploy')"
     runs-on: ubuntu-latest
@@ -43,8 +99,6 @@ jobs:
           access-tokens = github.com=${{ secrets.GITHUB_TOKEN }}
     - uses: actions/cache@v2
       with:
-        path: |
-          /nix/store
         key: nki-nix-${{ github.sha }}
         restore-keys: |
           nki-nix-