Rewrite switch-to-configuration in Perl

This will make it more efficient to do systemd dependency graph
processing (if necessary).

modules/system/activation/switch-to-configuration.pl

@@ -0,0 +1,57 @@
+#! @perl@
+
+use strict;
+use warnings;
+use File::Slurp;
+
+my $action = shift @ARGV;
+
+if (!defined $action || ($action ne "switch" && $action ne "boot" && $action ne "test")) {
+    print STDERR <<EOF;
+Usage: $0 [switch|boot|test]
+
+switch: make the configuration the boot default and activate now
+boot:   make the configuration the boot default
+test:   activate the configuration, but don\'t make it the boot default
+EOF
+    exit 1;
+}
+
+die "This is not a NixOS installation (/etc/NIXOS is missing)!\n" unless -f "/etc/NIXOS";
+
+# Install or update the bootloader.
+#system("@installBootLoader@ @out@") == 0 or exit 1 if $action eq "switch" || $action eq "boot";
+exit 0 if $action eq "boot";
+
+# Check if we can activate the new configuration.
+my $oldVersion = read_file("/run/current-system/init-interface-version", err_mode => 'quiet') // "";
+my $newVersion = read_file("@out@/init-interface-version");
+
+if ($newVersion ne $oldVersion) {
+    print STDERR <<EOF;
+Warning: the new NixOS configuration has an ‘init’ that is
+incompatible with the current configuration.  The new configuration
+won\'t take effect until you reboot the system.
+EOF
+    exit 100;
+}
+
+# Ignore SIGHUP so that we're not killed if we're running on (say)
+# virtual console 1 and we restart the "tty1" unit.
+$SIG{PIPE} = "IGNORE";
+
+# Activate the new configuration (i.e., update /etc, make accounts,
+# and so on).
+my $res = 0;
+print STDERR "activating the configuration...\n";
+system("@out@/activate", "@out@") == 0 or $res = 2;
+
+# FIXME: Re-exec systemd if necessary.
+
+# Make systemd reload its units.
+system("@systemd@/bin/systemctl", "daemon-reload") == 0 or $res = 3;
+
+# Signal dbus to reload its configuration.
+system("@systemd@/bin/systemctl", "reload", "dbus.service");
+
+exit $res;

modules/system/activation/switch-to-configuration.sh

@@ -1,59 +0,0 @@
-#! @shell@
-
-set -e
-export PATH=/empty
-for i in @path@; do PATH=$PATH:$i/bin:$i/sbin; done
-action="$1"
-
-if ! test -e /etc/NIXOS; then
-    echo "This is not a NixOS installation (/etc/NIXOS) is missing!"
-    exit 1
-fi
-
-if test -z "$action"; then
-    cat <<EOF
-Usage: $0 [switch|boot|test]
-
-switch: make the configuration the boot default and activate now
-boot:   make the configuration the boot default
-test:   activate the configuration, but don't make it the boot default
-EOF
-    exit 1
-fi
-
-# Install or update the bootloader.
-if [ "$action" = "switch" -o "$action" = "boot" ]; then
-    @installBootLoader@ @out@
-fi
-
-# Activate the new configuration.
-if [ "$action" != switch -a "$action" != test ]; then exit 0; fi
-
-oldVersion="$(cat /run/current-system/init-interface-version 2> /dev/null || echo "")"
-newVersion="$(cat @out@/init-interface-version)"
-
-if [ "$oldVersion" != "$newVersion" ]; then
-        cat <<EOF
-Warning: the new NixOS configuration has an ‘init’ that is
-incompatible with the current configuration.  The new configuration
-won't take effect until you reboot the system.
-EOF
-        exit 100 # denotes "reboot required" to Charon
-fi
-
-# Ignore SIGHUP so that we're not killed if we're running on (say)
-# virtual console 1 and we restart the "tty1" job.
-trap "" SIGHUP
-
-# Activate the new configuration (i.e., update /etc, make accounts,
-# and so on).
-echo "activating the configuration..."
-@out@/activate @out@
-
-# FIXME: Re-exec systemd if necessary.
-
-# Make systemd reload its jobs.
-systemctl daemon-reload
-
-# Signal dbus to reload its configuration.
-systemctl reload dbus.service || true

modules/system/activation/top-level.nix

@@ -114,7 +114,7 @@ let
 
       ln -s ${config.system.build.etc}/etc $out/etc
       ln -s ${config.system.path} $out/sw
-      ln -s ${pkgs.systemd} $out/systemd
+      ln -s "$systemd" $out/systemd
       ln -s ${config.hardware.firmware} $out/firmware
 
       echo -n "$kernelParams" > $out/kernel-params
@@ -130,7 +130,7 @@ let
       done
 
       mkdir $out/bin
-      substituteAll ${./switch-to-configuration.sh} $out/bin/switch-to-configuration
+      substituteAll ${./switch-to-configuration.pl} $out/bin/switch-to-configuration
       chmod +x $out/bin/switch-to-configuration
 
       ${config.system.extraSystemBuilderCmds}
@@ -146,6 +146,9 @@ let
     name = "nixos-${config.system.nixosVersion}";
     preferLocalBuild = true;
     buildCommand = systemBuilder;
+
+    inherit (pkgs) systemd;
+
     inherit children;
     kernelParams =
       config.boot.kernelParams ++ config.boot.extraKernelParams;
@@ -164,17 +167,10 @@ let
     # to the activation script.
     noRestartIfChanged = attrValues (mapAttrs (n: v: if v.restartIfChanged then [] else ["[${v.name}]=1"]) config.jobs);
 
-    # Most of these are needed by grub-install.
-    path =
-      [ pkgs.coreutils
-        pkgs.gnused
-        pkgs.gnugrep
-        pkgs.findutils
-        pkgs.diffutils
-        pkgs.systemd
-      ];
-
     configurationName = config.boot.loader.grub.configurationName;
+
+    # Needed by switch-to-configuration.
+    perl = "${pkgs.perl}/bin/perl -I${pkgs.perlPackages.FileSlurp}/lib/perl5/site_perl";
   };