guix-install.sh: Prompt for configuring substitutes discovery.

Also ensure prompt_yes_no always print the message with a trailing space,
which is more pleasing to the eye.

* etc/guix-daemon.conf.in <--discover=no>: New guix-daemon option.
* etc/guix-daemon.service.in: Likewise.
* etc/init.d/guix-daemon.in: Likewise.
* etc/openrc/guix-daemon.in: Likewise.
* etc/guix-install.sh (configure_substitute_discovery): New procedure.
(sys_enable_guix_daemon): Ask the user whether automatic substitute discovery
should be enabled.  Set the '--discover' argument accordingly.
(prompt_yes_no): Add a trailing space to the message.
(sys_authorize_build_farms): Remove trailing space from the message argument.
* NEWS (Distribution): Add news.

NEWS

@@ -14,8 +14,9 @@ Please send Guix bug reports to bug-guix@gnu.org.
 
 * Changes in 1.4.0 (since 1.3.0)
 ** Package management
-   * New 'deb' format for the 'guix pack' command
+*** New 'deb' format for the 'guix pack' command
-
+** Distribution
+*** The installation script can now enable local substitute servers discovery
 * Changes in 1.3.0 (since 1.2.0)
 ** Package management
 *** POWER9 (powerpc64le-linux) is now supported as a technology preview

etc/guix-daemon.conf.in

@@ -7,4 +7,4 @@ start on runlevel [2345]
 
 stop on runlevel [016]
 
-exec @localstatedir@/guix/profiles/per-user/root/current-guix/bin/guix-daemon --build-users-group=guixbuild
+exec @localstatedir@/guix/profiles/per-user/root/current-guix/bin/guix-daemon --build-users-group=guixbuild --discover=no

etc/guix-daemon.service.in

@@ -6,7 +6,8 @@
 Description=Build daemon for GNU Guix
 
 [Service]
-ExecStart=@localstatedir@/guix/profiles/per-user/root/current-guix/bin/guix-daemon --build-users-group=guixbuild
+ExecStart=@localstatedir@/guix/profiles/per-user/root/current-guix/bin/guix-daemon \
+    --build-users-group=guixbuild --discover=no
 Environment='GUIX_LOCPATH=@localstatedir@/guix/profiles/per-user/root/guix-profile/lib/locale' LC_ALL=en_US.utf8
 RemainAfterExit=yes
 StandardOutput=syslog

etc/guix-install.sh

@@ -249,6 +249,16 @@ chk_sys_nscd()
     fi
 }
 
+# Configure substitute discovery according to user's preferences.
+# $1 is the installed service file to edit.
+configure_substitute_discovery() {
+    if grep -q -- '--discover=no' "$1" && \
+            prompt_yes_no "Would you like the Guix daemon to automatically \
+discover substitute servers on the local network? (yes/no)"; then
+        sed -i 's/--discover=no/--discover=yes/' "$1"
+    fi
+}
+
 # ------------------------------------------------------------------------------
 #+MAIN
 
@@ -397,6 +407,7 @@ sys_enable_guix_daemon()
             { initctl reload-configuration;
               cp "~root/.config/guix/current/lib/upstart/system/guix-daemon.conf" \
                  /etc/init/ &&
+                  configure_substitute_discovery /etc/init/guix-daemon.conf &&
                   start guix-daemon; } &&
                 _msg "${PAS}enabled Guix daemon via upstart"
             ;;
@@ -426,6 +437,9 @@ sys_enable_guix_daemon()
                        -e 's/^Environment=\(.*\)$/Environment=\1 LC_ALL=en_US.UTF-8';
               fi;
 
+              configure_substitute_discovery \
+                  /etc/systemd/system/guix-daemon.service
+
               systemctl daemon-reload &&
                   systemctl enable guix-daemon &&
                   systemctl start  guix-daemon; } &&
@@ -437,6 +451,8 @@ sys_enable_guix_daemon()
                  /etc/init.d/guix-daemon;
               chmod 775 /etc/init.d/guix-daemon;
 
+              configure_substitute_discovery /etc/init.d/guix-daemon
+
               update-rc.d guix-daemon defaults &&
                   update-rc.d guix-daemon enable &&
                   service guix-daemon start; } &&
@@ -448,6 +464,8 @@ sys_enable_guix_daemon()
                  /etc/init.d/guix-daemon;
               chmod 775 /etc/init.d/guix-daemon;
 
+              configure_substitute_discovery /etc/init.d/guix-daemon
+
               rc-update add guix-daemon default &&
                   rc-service guix-daemon start; } &&
                 _msg "${PAS}enabled Guix daemon via OpenRC"

etc/init.d/guix-daemon.in

@@ -36,7 +36,7 @@ start)
       -E LC_ALL=en_US.utf8 \
       -p "/var/run/guix-daemon.pid" \
       @localstatedir@/guix/profiles/per-user/root/current-guix/bin/guix-daemon \
-      --build-users-group=guixbuild
+      --build-users-group=guixbuild --discover=no
   fi
   ;;
 stop)

etc/openrc/guix-daemon.in

@@ -20,7 +20,7 @@
 export GUIX_LOCPATH=@localstatedir@/guix/profiles/per-user/root/guix-profile/lib/locale
 export LC_ALL=en_US.utf8
 command="@localstatedir@/guix/profiles/per-user/root/current-guix/bin/guix-daemon"
-command_args="--build-users-group=guixbuild"
+command_args="--build-users-group=guixbuild --discover=no"
 command_background="yes"
 pidfile="/var/run/guix-daemon.pid"