Move initial channel generation into a separate module

modules/installer/cd-dvd/channel.nix

@@ -0,0 +1,38 @@
+# Provide an initial copy of the NixOS channel so that the user
+# doesn't need to run "nix-channel --update" first.
+
+{ config, pkgs, ... }:
+
+with pkgs.lib;
+
+let
+
+  # We need a copy of the Nix expressions for Nixpkgs and NixOS on the
+  # CD.  These are installed into the "nixos" channel of the root
+  # user, as expected by nixos-rebuild/nixos-install.
+  channelSources = pkgs.runCommand "nixos-${config.system.nixosVersion}"
+    { expr = builtins.readFile ../../../lib/channel-expr.nix; }
+    ''
+      mkdir -p $out/nixos
+      cp -prd ${cleanSource ../../..} $out/nixos/nixos
+      cp -prd ${cleanSource <nixpkgs>} $out/nixos/nixpkgs
+      chmod -R u+w $out/nixos/nixos
+      echo -n ${config.system.nixosVersion} > $out/nixos/nixos/.version
+      echo -n "" > $out/nixos/nixos/.version-suffix
+      echo "$expr" > $out/nixos/default.nix
+    '';
+
+in
+
+{
+  # Provide the NixOS/Nixpkgs sources in /etc/nixos.  This is required
+  # for nixos-install.
+  boot.postBootCommands =
+    ''
+      echo "unpacking the NixOS/Nixpkgs sources..."
+      mkdir -p /nix/var/nix/profiles/per-user/root
+      ${config.environment.nix}/bin/nix-env -p /nix/var/nix/profiles/per-user/root/channels -i ${channelSources} --quiet
+      mkdir -m 0700 -p /root/.nix-defexpr
+      ln -s /nix/var/nix/profiles/per-user/root/channels /root/.nix-defexpr/channels
+    '';
+}

modules/installer/cd-dvd/installation-cd-base.nix

@@ -5,31 +5,11 @@
 
 with pkgs.lib;
 
-let
-
-  # We need a copy of the Nix expressions for Nixpkgs and NixOS on the
-  # CD.  These are installed into the "nixos" channel of the root
-  # user, as expected by nixos-rebuild/nixos-install.
-  channelSources = pkgs.runCommand "nixos-${config.system.nixosVersion}"
-    { expr = builtins.readFile ../../../lib/channel-expr.nix; }
-    ''
-      mkdir -p $out/nixos
-      cp -prd ${cleanSource ../../..} $out/nixos/nixos
-      cp -prd ${cleanSource <nixpkgs>} $out/nixos/nixpkgs
-      chmod -R u+w $out/nixos/nixos
-      echo -n ${config.system.nixosVersion} > $out/nixos/nixos/.version
-      echo -n "" > $out/nixos/nixos/.version-suffix
-      echo "$expr" > $out/nixos/default.nix
-    '';
-
-  includeSources = true;
-
-in
-
 {
   require =
     [ ./memtest.nix
       ./iso-image.nix
+      ./channel.nix
 
       # Profiles of this basic installation CD.
       ../../profiles/all-hardware.nix
@@ -42,17 +22,6 @@ in
 
   isoImage.volumeID = "NIXOS_${config.system.nixosVersion}";
 
-  # Provide the NixOS/Nixpkgs sources in /etc/nixos.  This is required
-  # for nixos-install.
-  boot.postBootCommands = optionalString includeSources
-    ''
-      echo "unpacking the NixOS/Nixpkgs sources..."
-      mkdir -p /nix/var/nix/profiles/per-user/root
-      ${config.environment.nix}/bin/nix-env -p /nix/var/nix/profiles/per-user/root/channels -i ${channelSources} --quiet
-      mkdir -m 0700 -p /root/.nix-defexpr
-      ln -s /nix/var/nix/profiles/per-user/root/channels /root/.nix-defexpr/channels
-    '';
-
   # Make the installer more likely to succeed in low memory
   # environments.  The kernel's overcommit heustistics bite us
   # fairly often, preventing processes such as nix-worker or