chore(ci): Setup cachix, then push & pin

.github/workflows/ci.yaml

@@ -12,8 +12,17 @@ jobs:
     strategy:
       matrix:
         # Intel mac excluded; See https://github.com/juspay/services-flake/issues/231
-        system: [ x86_64-linux, aarch64-darwin ]
+        system: [x86_64-linux, aarch64-darwin]
     steps:
       - uses: actions/checkout@v4
+      - uses: cachix/cachix-action@v14
+        with:
+          name: services-flake
+          authToken: "${{ secrets.CACHIX_AUTH_TOKEN }}"
+          skipPush: true
       - name: om ci
         run: om ci --extra-access-tokens "github.com=${{ secrets.GITHUB_TOKEN }}" run --systems "${{ matrix.system }}"
+      # Push the Nix cache
+      - name: Push to cachix
+        # if: github.ref == 'refs/heads/main'
+        run: nix --option system "${{ matrix.system }}" run .#cachix-push

dev/flake.nix

@@ -9,6 +9,8 @@
       inputs.nixpkgs.follows = "nixpkgs";
       inputs.nixpkgs-stable.follows = "nixpkgs";
     };
+    cachix-push.url = "github:juspay/cachix-push";
+
     # CI will override `services-flake` to run checks on the latest source
     services-flake.url = "github:juspay/services-flake";
   };
@@ -19,9 +21,10 @@
         inputs.flake-root.flakeModule
         inputs.treefmt-nix.flakeModule
         inputs.pre-commit-hooks-nix.flakeModule
+        inputs.cachix-push.flakeModule
         ./nix/pre-commit.nix
       ];
-      perSystem = { pkgs, lib, config, ... }: {
+      perSystem = { self', pkgs, config, ... }: {
         treefmt = {
           projectRoot = inputs.services-flake;
           projectRootFile = "flake.nix";
@@ -32,6 +35,12 @@
             nixpkgs-fmt.enable = true;
           };
         };
+        cachix-push = {
+          cacheName = "services-flake";
+          pathsToCache = {
+            devshell = self'.devShells.default;
+          };
+        };
         devShells.default = pkgs.mkShell {
           packages = with pkgs; [
             just