Extracted out duplicate binary cache config

NixSupport/nixosModules/app.nix

@@ -5,15 +5,12 @@ in
 {
     imports = [
         ihp.nixosModules.options
+        ihp.nixosModules.binaryCache
         ihp.nixosModules.services_app
         ihp.nixosModules.services_worker
         ihp.nixosModules.services_migrate
     ];
 
-    # Speed up builds with the IHP binary cache
-    nix.settings.substituters = [ "https://digitallyinduced.cachix.org" ];
-    nix.settings.trusted-public-keys = [ "digitallyinduced.cachix.org-1:y+wQvrnxQ+PdEsCt91rmvv39qRCYzEgGQaldK26hCKE=" ];
-
     # Pin the nixpkgs to the IHP nixpkgs
     nix.registry.nixpkgs.flake = nixpkgs;
 }

NixSupport/nixosModules/appWithPostgres.nix

@@ -1,18 +1,18 @@
 # Running IHP app + a local Postgres connected to it
-{ config, pkgs, modulesPath, lib, ihp, ... }:
+{ config, nixpkgs, pkgs, modulesPath, lib, ihp, ... }:
 let cfg = config.services.ihp;
 in
 {
     imports = [
         ihp.nixosModules.options
+        ihp.nixosModules.binaryCache
         ihp.nixosModules.services_app
         ihp.nixosModules.services_worker
         ihp.nixosModules.services_migrate
     ];
 
-    # Speed up builds with the IHP binary cache
-    nix.settings.substituters = [ "https://digitallyinduced.cachix.org" ];
-    nix.settings.trusted-public-keys = [ "digitallyinduced.cachix.org-1:y+wQvrnxQ+PdEsCt91rmvv39qRCYzEgGQaldK26hCKE=" ];
+    # Pin the nixpkgs to the IHP nixpkgs
+    nix.registry.nixpkgs.flake = nixpkgs;
 
     # Add swap to avoid running out of memory during builds
     swapDevices = [ { device = "/swapfile"; size = 8192; } ];

NixSupport/nixosModules/binaryCache.nix

@@ -0,0 +1,8 @@
+# Configures the IHP binary cache
+{ config, nixpkgs, pkgs, modulesPath, lib, ihp, ... }:
+{
+    # Speed up builds with the IHP binary cache
+    nix.settings.substituters = lib.mkAfter [ "https://digitallyinduced.cachix.org" ];
+    nix.settings.trusted-public-keys = lib.mkAfter[ "digitallyinduced.cachix.org-1:y+wQvrnxQ+PdEsCt91rmvv39qRCYzEgGQaldK26hCKE=" ];
+}
+

flake.nix

@@ -47,6 +47,7 @@
                     services_worker = ./NixSupport/nixosModules/services/worker.nix;
                     services_migrate = ./NixSupport/nixosModules/services/migrate.nix;
                     options = ./NixSupport/nixosModules/options.nix;
+                    binaryCache = ./NixSupport/nixosModules/binaryCache.nix;
                 };
             };
         }