services: postgresql-service-type: Allow allowing to log into the user.

It is often useful to be able to use the `postgres' user for management tasks,
so this commit allows setting that.  The default behavior is not changed.

I have also added missing exports and sorted them by alphabet.

* gnu/services/databases.scm (%default-home-directory): New variable.
(<postgresql-configuration>): Add home-directory, allow-login? fields.
(create-postgresql-account): Use them.
* doc/guix.texi (Database Services): Document it.

Change-Id: I2212e5082ff4e87c49a5a8a4711bf929dd08626a
Signed-off-by: Ludovic Courtès <ludo@gnu.org>
Modified-by: Ludovic Courtès <ludo@gnu.org>

doc/guix.texi

@@ -27527,11 +27527,11 @@ don't need the cluster anymore, delete @var{data-directory}), then
 restart the service.
 
 Peer authentication is used by default and the @code{postgres} user
-account has no shell, which prevents the direct execution of @code{psql}
-commands as this user.  To use @code{psql}, you can temporarily log in
-as @code{postgres} using a shell, create a PostgreSQL superuser with the
-same name as one of the system users and then create the associated
-database.
+account has no shell (unless @code{allow-login?} is @code{#t}), which
+prevents the direct execution of @code{psql} commands as this user.  To
+use @code{psql}, you can temporarily log in as @code{postgres} using a
+shell, create a PostgreSQL superuser with the same name as one of the
+system users and then create the associated database.
 
 @example
 sudo -u postgres -s /bin/sh
@@ -27610,6 +27610,13 @@ required to add extensions provided by other packages.
 @item @code{create-account?} (default: @code{#t})
 Whether or not the @code{postgres} user and group should be created.
 
+@item @code{allow-login?} (default: @code{#f})
+Whether or not to allow login into the created account.
+
+@item @code{home-directory} (default: @code{"/var/empty"})
+The home directory of the user.  It is strongly advised to change this
+if you set @code{allow-login?} to @code{#t}.
+
 @item @code{uid} (default: @code{#f})
 Explicitly specify the UID of the @code{postgres} daemon account.
 You normally do not need to specify this, in which case a free UID will

gnu/services/databases.scm

@@ -29,6 +29,7 @@
   #:use-module (gnu services)
   #:use-module (gnu services shepherd)
   #:use-module (gnu system shadow)
+  #:autoload   (gnu system accounts) (default-shell)
   #:use-module (gnu packages admin)
   #:use-module (gnu packages base)
   #:use-module (gnu packages databases)
@@ -51,13 +52,18 @@
 
             postgresql-configuration
             postgresql-configuration?
-            postgresql-configuration-postgresql
-            postgresql-configuration-port
-            postgresql-configuration-locale
-            postgresql-configuration-file
-            postgresql-configuration-log-directory
+            postgresql-configuration-allow-login?
+            postgresql-configuration-create-account?
             postgresql-configuration-data-directory
             postgresql-configuration-extension-packages
+            postgresql-configuration-file
+            postgresql-configuration-gid
+            postgresql-configuration-home-directory
+            postgresql-configuration-locale
+            postgresql-configuration-log-directory
+            postgresql-configuration-port
+            postgresql-configuration-postgresql
+            postgresql-configuration-uid
 
             postgresql-service
             postgresql-service-type
@@ -164,6 +170,8 @@ host	all	all	::1/128 	md5"))
              port)))
       #:local-build? #t))))
 
+(define %default-home-directory "/var/empty")
+
 (define-record-type* <postgresql-configuration>
   postgresql-configuration make-postgresql-configuration
   postgresql-configuration?
@@ -186,6 +194,10 @@ host	all	all	::1/128 	md5"))
                       (default '()))
   (create-account?    postgresql-configuration-create-account?
                       (default #t))
+  (home-directory     postgresql-configuration-home-directory
+                      (default %default-home-directory))
+  (allow-login?       postgresql-configuration-allow-login?
+                      (default #f))
   (uid                postgresql-configuration-uid
                       (default #f))
   (gid                postgresql-configuration-gid
@@ -193,7 +205,7 @@ host	all	all	::1/128 	md5"))
 
 (define (create-postgresql-account config)
   (match-record config <postgresql-configuration>
-    (create-account? uid gid)
+                (create-account? allow-login? home-directory uid gid)
     (if (not create-account?) '()
         (list (user-group
                (name "postgres")
@@ -205,8 +217,12 @@ host	all	all	::1/128 	md5"))
                (system? #t)
                (uid uid)
                (comment "PostgreSQL server user")
-               (home-directory "/var/empty")
-               (shell (file-append shadow "/sbin/nologin")))))))
+               (create-home-directory?
+                (not (string=? home-directory %default-home-directory)))
+               (home-directory home-directory)
+               (shell (if allow-login?
+                          (default-shell)
+                          (file-append shadow "/sbin/nologin"))))))))
 
 (define (final-postgresql postgresql extension-packages)
   (if (null? extension-packages)