system: install: Always use 'current-guix'.

Fixes <https://issues.guix.gnu.org/53210>.
Reported by Mathieu Othacehe <othacehe@gnu.org>.

* gnu/system/install.scm (%installation-services): Set 'guix' to
use (current-guix) in 'guix-configuration'.
* gnu/system/examples/vm-image.tmpl: Likewise.
* gnu/tests/install.scm (operating-system-with-current-guix): Remove.
(run-install, installation-os-for-gui-tests): Remove its uses.
* Makefile.am (release): Remove intermediate use of
'update-guix-package.scm' and subsequent 'git commit' invocation.

Makefile.am

@@ -977,14 +977,9 @@ release: dist-with-updated-version all
 	  mv "guix-binary.$$system.tar.xz"					\
 	      "$(releasedir)/guix-binary-$(PACKAGE_VERSION).$$system.tar.xz" ;	\
 	done
-# Bump the Guix package version and build it (again).
-	GUIX_ALLOW_ME_TO_USE_PRIVATE_COMMIT=yes \
-	$(top_builddir)/pre-inst-env "$(GUILE)"	\
-		$(top_srcdir)/build-aux/update-guix-package.scm	\
-		"`git rev-parse HEAD`"
-	git add $(top_srcdir)/gnu/packages/package-management.scm
-	git commit -m "gnu: guix: Update to `git rev-parse HEAD | cut -c1-7`."
-	$(top_builddir)/pre-inst-env guix build guix			\
+# Build 'current-guix' to speed things up for the next step.
+	$(top_builddir)/pre-inst-env guix build				\
+	      -e '((@ (gnu packages package-management) current-guix))'	\
 	      $(call system_flags,$(GUIX_SYSTEM_SUPPORTED_SYSTEMS))	\
 	      -v1 --no-grafts --fallback
 # Generate the ISO installation images.

gnu/system/examples/vm-image.tmpl

@@ -123,7 +123,14 @@ root ALL=(ALL) ALL
                      (login-service-type config =>
                                          (login-configuration
                                           (inherit config)
-                                          (motd vm-image-motd)))))))
+                                          (motd vm-image-motd)))
+
+                     ;; Install and run the current Guix rather than an older
+                     ;; snapshot.
+                     (guix-service-type config =>
+                                        (guix-configuration
+                                         (inherit config)
+                                         (guix (current-guix))))))))
 
   ;; Allow resolution of '.local' host names with mDNS.
   (name-service-switch %mdns-host-lookup-nss))

gnu/system/install.scm

@@ -357,11 +357,17 @@ Access documentation at any time by pressing Alt-F2.\x1b[0m
            ;; network.  It can be faster than fetching from remote servers.
            (service avahi-service-type)
 
-           ;; The build daemon.  Register the default substitute server key(s)
-           ;; as trusted to allow the installation process to use substitutes by
-           ;; default.
+           ;; The build daemon.
            (service guix-service-type
-                    (guix-configuration (authorize-key? #t)))
+                    (guix-configuration
+                     ;; Register the default substitute server key(s) as
+                     ;; trusted to allow the installation process to use
+                     ;; substitutes by default.
+                     (authorize-key? #t)
+
+                     ;; Install and run the current Guix rather than an older
+                     ;; snapshot.
+                     (guix (current-guix))))
 
            ;; Start udev so that useful device nodes are available.
            ;; Use device-mapper rules for cryptsetup & co; enable the CRDA for

gnu/tests/install.scm

@@ -152,15 +152,6 @@
                                                   (guix combinators)))))
                     %base-services))))
 
-(define (operating-system-with-current-guix os)
-  "Return a variant of OS that uses the current Guix."
-  (operating-system
-    (inherit os)
-    (services (modify-services (operating-system-user-services os)
-                (guix-service-type config =>
-                                   (guix-configuration
-                                    (inherit config)
-                                    (guix (current-guix))))))))
 
 
 (define MiB (expt 2 20))
@@ -232,8 +223,7 @@ reboot\n")
                              ;; Since the image has no network access, use the
                              ;; current Guix so the store items we need are in
                              ;; the image and add packages provided.
-                             (inherit (operating-system-with-current-guix
-                                       installation-os))
+                             (inherit installation-os)
                              (kernel-arguments '("console=ttyS0")))
                            #:imported-modules '((gnu services herd)
                                                 (gnu installer tests)
@@ -1865,8 +1855,7 @@ build (current-guix) and then store a couple of full system images.")
    (operating-system
      (inherit (operating-system-with-console-syslog
                (operating-system-add-packages
-                (operating-system-with-current-guix
-                 installation-os)
+                installation-os
                 %extra-packages)))
      (kernel-arguments '("console=ttyS0")))
    #:imported-modules '((gnu services herd)