postgres: make setup a bit more verbose

example/flake.nix

@@ -0,0 +1,54 @@
+{
+  description = "A demo of sqlite-web";
+  inputs = {
+    nixpkgs.url = "github:nixos/nixpkgs/nixpkgs-unstable";
+    flake-parts.url = "github:hercules-ci/flake-parts";
+    systems.url = "github:nix-systems/default";
+    process-compose-flake.url = "github:Platonic-Systems/process-compose-flake";
+    services-flake.url = "github:juspay/services-flake";
+
+    northwind.url = "github:pthom/northwind_psql";
+    northwind.flake = false;
+  };
+  outputs = inputs:
+    inputs.flake-parts.lib.mkFlake { inherit inputs; } {
+      systems = import inputs.systems;
+      imports = [
+        inputs.process-compose-flake.flakeModule
+      ];
+      perSystem = { self', pkgs, lib, ... }: {
+        # This adds a `self.packages.default`
+        process-compose."default" = { config, ... }:
+          {
+            imports = [
+              inputs.services-flake.processComposeModules.default
+            ];
+
+            services.postgres = {
+              enable = true;
+              listen_addresses = "127.0.0.1";
+              initialDatabases = [
+                { 
+                  name = "sample"; 
+                  schema = "${inputs.northwind}/northwind.sql";
+                } 
+              ];
+            };
+
+            settings.processes.pgweb = {
+              environment.PGWEB_DATABASE_URL = "postgres://srid@127.0.0.1:5432/sample";
+              command = pkgs.pgweb;
+              depends_on."postgres".condition = "process_started";
+            };
+
+            # Set this attribute and get NixOS VM tests, as a flake check, for free.
+            testScript = ''
+              process_compose.wait_until(lambda procs:
+                procs["postgres"]["status"] == "Running"
+              )
+              machine.succeed("echo 'SELECT version();' | ${config.services.postgres.package}/bin/psql -h 127.0.0.1 -U tester chinook")
+            '';
+          };
+      };
+    };
+}

nix/postgres.nix

@@ -242,13 +242,18 @@ in
               export PATH=${postgresPkg}/bin:${pkgs.coreutils}/bin
 
               if [[ ! -d "$PGDATA" ]]; then
+                set -x
                 initdb ${lib.concatStringsSep " " cfg.initdbArgs}
+                set +x
                 ${setupInitialDatabases}
 
                 ${runInitialScript}
+              else
+                echo "Postgres data directory already exists. Skipping initialization."
               fi
 
               # Setup config
+              set -x
               cp ${configFile} "$PGDATA/postgresql.conf"
             '';
           in