feat(.github): use Nix shell for Github Actions steps

.github/actions/nix-setup/action.yaml

@@ -0,0 +1,20 @@
+---
+name: Setup Nix and direnv
+description: |
+  Sets up the Nix package manager and direnv to use the same packages
+  vendored through Nix for local development.
+inputs:
+  github_token:
+    description: 'Github Access Token'
+    required: true
+runs:
+  using: composite
+  steps:
+    - name: Install Nix package manager
+      uses: cachix/install-nix-action@v22
+      with:
+        github_access_token: ${{ inputs.github_token }}
+        extra_nix_config: |
+          experimental-features = nix-command flakes
+    - name: Set up Nix cache
+      uses: DeterminateSystems/magic-nix-cache-action@v2

.github/workflows/ci.yml

@@ -59,6 +59,51 @@ jobs:
         env:
           DATABASE_URL: postgres://eventually:password@localhost:5432/eventually?sslmode=disable
 
+  nix-test:
+    name: Test [Nix]
+    runs-on: ubuntu-latest
+    continue-on-error: ${{ matrix.required }}
+    strategy:
+      matrix:
+        build: [stable, nightly]
+        include:
+          - build: stable
+            required: true
+            toolchain: stable
+          - build: nightly
+            required: false
+            toolchain: nightly
+
+    services:
+      postgres:
+        env:
+          POSTGRES_USER: eventually
+          POSTGRES_PASSWORD: password
+          POSTGRES_DB: eventually
+        image: postgres:latest
+        ports: ["5432:5432"]
+        options: >-
+          --health-cmd pg_isready
+          --health-interval 10s
+          --health-timeout 5s
+          --health-retries 5
+
+    steps:
+      - name: Checkout source code
+        uses: actions/checkout@v4
+      - name: Set up Nix system
+        uses: ./.github/actions/nix-setup
+        with:
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+      - name: Preload nix-develop shell
+        run: nix develop .#${{ matrix.toolchain }} --verbose -c echo "nix-develop shell loaded!"
+      - name: Rust cache
+        uses: Swatinem/rust-cache@v2
+      - name: Run 'cargo test'
+        run: nix develop .#${{ matrix.toolchain }} --verbose -c cargo test --workspace --all-features
+        env:
+          DATABASE_URL: postgres://eventually:password@localhost:5432/eventually?sslmode=disable
+
   coverage:
     name: Code Coverage
     runs-on: ubuntu-latest

flake.nix

@@ -19,20 +19,55 @@
 
           pkgs = import nixpkgs {
             inherit system overlays;
+            config.allowBroken = true;
           };
 
-          nativeBuildInputs = with pkgs; [ rust-bin.nightly.latest.default protobuf3_24 ];
+          nativeBuildInputs = with pkgs; [ protobuf3_24 ];
 
           buildInputs = with pkgs; [ pkg-config openssl ] ++ lib.optionals stdenv.isDarwin [
             darwin.apple_sdk.frameworks.SystemConfiguration
           ];
+
+          packages = with pkgs; [
+            cargo-llvm-cov
+          ];
+
+          defaultShell = with pkgs; mkShell {
+            inherit buildInputs packages;
+
+            nativeBuildInputs = with pkgs; nativeBuildInputs ++ [
+              rust-bin.nightly.latest.default
+            ];
+
+            PROTOC = "${protobuf3_24}/bin/protoc";
+          };
         in
         with pkgs;
         {
-          devShells.default = with pkgs; mkShell {
-            inherit nativeBuildInputs buildInputs;
+          devShells = rec {
+            default = nightly;
 
-            PROTOC = "${protobuf3_24}/bin/protoc";
+            nightly = with pkgs; mkShell {
+              inherit buildInputs packages;
+
+              nativeBuildInputs = with pkgs; nativeBuildInputs ++ [
+                rust-bin.nightly.latest.default
+              ];
+
+              PROTOC = "${protobuf3_24}/bin/protoc";
+            };
+
+            stable = with pkgs; mkShell {
+              name = "stable";
+
+              inherit buildInputs packages;
+
+              nativeBuildInputs = with pkgs; nativeBuildInputs ++ [
+                rust-bin.stable.latest.default
+              ];
+
+              PROTOC = "${protobuf3_24}/bin/protoc";
+            };
           };
         }
       );