modules: services: add postgresql

Enable the service itself in other modules when needed, but pin the
package in a single place.

modules/services/default.nix

@@ -20,6 +20,7 @@
     ./pirate.nix
     ./podgrab.nix
     ./postgresql-backup.nix
+    ./postgresql.nix
     ./quassel.nix
     ./rss-bridge.nix
     ./sabnzbd.nix

modules/services/drone.nix

@@ -81,6 +81,7 @@ in
     users.groups.drone = { };
 
     services.postgresql = {
+      enable = true;
       ensureDatabases = [ "drone" ];
       ensureUsers = [{
         name = "drone";

modules/services/matrix.nix

@@ -63,7 +63,6 @@ in
   config = lib.mkIf cfg.enable {
     services.postgresql = {
       enable = true;
-      package = pkgs.postgresql_12;
       initialScript = pkgs.writeText "synapse-init.sql" ''
         CREATE ROLE "matrix-synapse" WITH LOGIN PASSWORD 'synapse';
         CREATE DATABASE "matrix-synapse" WITH OWNER "matrix-synapse"

modules/services/postgresql.nix

@@ -0,0 +1,18 @@
+{ config, lib, pkgs, ... }:
+let
+  cfg = config.my.services.postgresql;
+in
+{
+  options.my.services.postgresql = with lib; {
+    enable = my.mkDisableOption "postgres configuration";
+  };
+
+  config = lib.mkMerge [
+    # Let other services enable postgres when they need it
+    (lib.mkIf cfg.enable {
+      services.postgresql = {
+        package = pkgs.postgresql_12;
+      };
+    })
+  ];
+}