services: databases: Don't specify a default postgresql version.

Currently, if the postgresql package major version changes, this is going to
break the service upon upgrade, because PostgreSQL will reject the data files
from the differing major version of the service.

Because it's important to either keep running a particular major version, or
intentionally upgrade, I think the configuration would be better with no
default. I think this is also going to be helpful when trying to assist users
upgrading PostgreSQL.

* gnu/services/databases.scm (<postgresql-configuration>): Remove default for
postgresql.
(postgresql-service-type): Remove the default value.
* gnu/tests/databases.scm (%postgresql-os): Update accordingly.
* gnu/tests/guix.scm (%guix-data-service-os): Update accordingly.
* gnu/tests/monitoring.scm (%zabbix-os): Update accordingly.
* gnu/tests/web.scm (patchwork-os): Update accordingly.
* doc/guix.texi (PostgreSQL): Update accordingly.

doc/guix.texi

@@ -18457,7 +18457,9 @@ The following example describes a PostgreSQL service with the default
 configuration.
 
 @lisp
-(service postgresql-service-type)
+(service postgresql-service-type
+         (postgresql-configuration
+          (postgresql postgresql-10)))
 @end lisp
 
 If the services fails to start, it may be due to an incompatible
@@ -18483,7 +18485,7 @@ Data type representing the configuration for the
 @code{postgresql-service-type}.
 
 @table @asis
-@item @var{postgresql} (default: @code{postgresql})
+@item @var{postgresql}
 PostgreSQL package to use for the service.
 
 @item @var{port} (default: @code{5432})

gnu/services/databases.scm

@@ -147,8 +147,7 @@ host	all	all	::1/128 	md5"))
 (define-record-type* <postgresql-configuration>
   postgresql-configuration make-postgresql-configuration
   postgresql-configuration?
-  (postgresql         postgresql-configuration-postgresql ;<package>
-                      (default postgresql))
+  (postgresql         postgresql-configuration-postgresql) ;<package>
   (port               postgresql-configuration-port
                       (default 5432))
   (locale             postgresql-configuration-locale
@@ -279,8 +278,7 @@ host	all	all	::1/128 	md5"))
                        (service-extension account-service-type
                                           (const %postgresql-accounts))
                        (service-extension profile-service-type
-                                          (compose list postgresql-configuration-postgresql))))
-                (default-value (postgresql-configuration))))
+                                          (compose list postgresql-configuration-postgresql))))))
 
 (define-deprecated (postgresql-service #:key (postgresql postgresql)
                                        (port 5432)

gnu/tests/databases.scm

@@ -215,7 +215,9 @@
 
 (define %postgresql-os
   (simple-operating-system
-   (service postgresql-service-type)))
+   (service postgresql-service-type
+            (postgresql-configuration
+             (postgresql postgresql-10)))))
 
 (define (run-postgresql-test)
   "Run tests in %POSTGRESQL-OS."

gnu/tests/guix.scm

@@ -156,6 +156,7 @@
    (service dhcp-client-service-type)
    (service postgresql-service-type
             (postgresql-configuration
+             (postgresql postgresql-10)
              (config-file
               (postgresql-config-file
                (hba-file

gnu/tests/monitoring.scm

@@ -307,7 +307,9 @@ zabbix||{}
   (let ((base-os
          (simple-operating-system
           (service dhcp-client-service-type)
-          (service postgresql-service-type)
+          (service postgresql-service-type
+                   (postgresql-configuration
+                    (postgresql postgresql-10)))
           (service zabbix-front-end-service-type
                    (zabbix-front-end-configuration
                     (db-password "zabbix")))

gnu/tests/web.scm

@@ -567,7 +567,9 @@ HTTP-PORT."
              (config
               (httpd-config-file
                (listen '("8080"))))))
-   (service postgresql-service-type)
+   (service postgresql-service-type
+            (postgresql-configuration
+             (postgresql postgresql-10)))
    (service patchwork-service-type
             (patchwork-configuration
              (patchwork patchwork)