add nix cache workflow

.github/workflows/nix.yml

@@ -0,0 +1,34 @@
+name: Build and cache with Nix
+
+on:
+  workflow_dispatch:
+  push:
+
+jobs:
+  build-and-cache:
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix:
+        os: [ubuntu-latest, macos-latest]
+    steps:
+    - name: Checkout repository
+      uses: actions/checkout@v3
+
+    - name: Set up Nix with caching
+      uses: kadena-io/setup-nix-with-cache@v1
+      with:
+        cache_url: s3://nixcache.chainweb.com?region=us-east-1
+        signing_private_key: ${{ secrets.NIX_CACHE_PRIVATE_KEY }}
+
+    - name: Set up AWS credentials
+      uses: aws-actions/configure-aws-credentials@v2
+      with:
+        aws-access-key-id: ${{ secrets.NIX_CACHE_AWS_ACCESS_KEY_ID }}
+        aws-secret-access-key: ${{ secrets.NIX_CACHE_AWS_SECRET_ACCESS_KEY }}
+        aws-region: us-east-1
+
+    - name: Build and cache artifacts
+      timeout-minutes: 740
+      run: |
+        echo Building the default package and its devShell
+        nix build .#check

flake.nix

@@ -41,17 +41,19 @@
             };
         })
       ];
-    in flake // {
+      # This package depends on other packages at buildtime, but its output does not
+      # depend on them. This way, we don't have to download the entire closure to verify
+      # that those packages build.
+      mkCheck = name: package: pkgs.runCommand ("check-"+name) {} ''
+        echo ${name}: ${package}
+        echo works > $out
+      '';
+    in flake // rec {
       packages.default = flake.packages."pact:exe:pact";
-
-      devShell = pkgs.haskellPackages.shellFor {
-        buildInputs = with pkgs.haskellPackages; [
-          cabal-install
-          haskell-language-server
-          # hlint
-        ];
-
-        withHoogle = true;
-      };
+      packages.check = pkgs.runCommand "check" {} ''
+        echo ${mkCheck "pact" packages.default}
+        echo ${mkCheck "devShell" flake.devShell}
+        echo works > $out
+      '';
     });
 }