Add Nix to CI testing

Author: berquist

.github/workflows/ci.yml

@@ -13,8 +13,10 @@ concurrency:
 jobs:
   prechecks:
     uses: ./.github/workflows/pre-commit.yml
-  all-prechecks:
-    needs: [prechecks]
+  nix:
+    uses: ./.github/workflows/nix.yml
+  all:
+    needs: [prechecks, nix]
     runs-on: ubuntu-latest
     steps:
       - name: Success

.github/workflows/nix.yml

@@ -0,0 +1,26 @@
+---
+name: build and test nix package
+
+# yamllint disable-line rule:truthy
+on:
+  workflow_dispatch:
+  workflow_call:
+
+concurrency:
+  group: nix-${{github.ref}}-${{github.event.pull_request.number || github.run_number}}
+  cancel-in-progress: true
+
+jobs:
+  nix-build:
+    runs-on: ubuntu-latest
+    steps:
+      # Install Nix on the runner
+      - uses: cachix/install-nix-action@17fe5fb4a23ad6cbbe47d6b3f359611ad276644c # v31
+        with:
+          nix_path: nixpkgs=channel:nixos-unstable
+      # Pull from the cachix cache
+      - uses: cachix/cachix-action@0fc020193b5a1fa3ac4575aa3a7d3aa6a35435ad # v16
+      # Checkout of the current head in the working dir
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4
+      - name: Check nix flake
+        run: nix flake check -L