ci: add Nix action

ci/nix.yml

@@ -0,0 +1,25 @@
+name: Nix
+
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/[email protected]
+    - name: Install Nix
+      uses: cachix/install-nix-action@v10
+    - name: Install Cachix
+    - uses: cachix/cachix-action@v6
+      with:
+        # Once you generate a binary cache on https://app.cachix.org, you'll need to insert the name of the cache here
+        name: mycache
+        signingKey: '${{ secrets.CACHIX_SIGNING_KEY }}'
+    - name: Run nix-build
+      run: nix-build
+    - name: Check nix-shell works
+      run: nix-shell --run "echo OK"

ci/properties/nix.properties.json

@@ -0,0 +1,6 @@
+{
+    "name": "Nix",
+    "description": "Build Nix project",
+    "iconName": "nix",
+    "categories": ["Nix"]
+}