nongnu: installation-os-nonfree: Add prefilled channels.scm to install image.

Remove requirement to define 'nonguix channel on build system.

    * nongnu/system/install.scm (installation-os-nonfree): Add channels.scm to skeletons
%channels (%channels, %channels-file)
(inferior-channel, linux, linux-firmware ): Add variables.

nongnu/system/install.scm

@@ -20,13 +20,73 @@
 (define-module (nongnu system install)
   #:use-module (gnu system)
   #:use-module (gnu system install)
-  #:use-module (nongnu packages linux)
+  #:use-module (guix channels)
+  #:use-module (guix ci)
+  #:use-module (guix gexp)
+  #:use-module (guix inferior)
+  #:use-module (ice-9 pretty-print)
   #:export (installation-os-nonfree))
 
+; List of guix channels. Used in both inferior-channel and the
+; "/etc/skel/.config/guix/channels.scm" definitions.
+; %default-guix-channel is configured to pull package definitions from
+; the Guix substitute server, to save compiling during a guix pull.
+(define %channels
+ '(list (channel
+          (name 'nonguix)
+          (url "https://gitlab.com/nonguix/nonguix")
+          (introduction
+          (make-channel-introduction
+           "897c1a470da759236cc11798f4e0a5f7d4d59fbc"
+            (openpgp-fingerprint
+             "2A39 3FFF 68F4 EF7A 3D29  12AF 6F51 20A0 22FB B2D5"))))
+    (channel-with-substitutes-available
+     %default-guix-channel
+     "https://ci.guix.gnu.org")))
+
+; Create the plain-file definition of "channels.scm" to add to the install.
+(define %channels-file
+  (let ((port (open-output-string)))
+    (pretty-print '(use-modules
+                     (guix ci)) ; for channel-with-substitutes-availabe
+                  port)
+    (pretty-print %channels
+                  port)
+    (plain-file "channels.scm"
+      (get-output-string port))))
+
+; inferior-for-channels allows for looking up packages WITHOUT a channel
+; definition in place. Requires the 'guix channel as well so reuse of the
+; %channels definition is done with eval.
+(define inferior-channel
+  (inferior-for-channels
+    (eval %channels
+          (current-dynamic-state))))
+
+(define linux ; latest linux package from inferior-channel
+  (car (lookup-inferior-packages inferior-channel
+                                 "linux")))
+
+(define linux-firmware ; latest linux-firmware package from inferior-channel
+  (car (lookup-inferior-packages inferior-channel
+                                 "linux-firmware")))
+
+; Currently the best way to add the "channels.scm" file to the install is via
+; the skeletons record type.
+; The following service definition for the global channel file is also viable:
+;   (service special-files-service-type
+;    `(("/etc/guix/channels.scm" ,%channel-file)))
+; However even when using (operating-system-services installation-os) without
+; modifying it, a "more than one target service of type 'account" error occurs.
 (define installation-os-nonfree
   (operating-system
     (inherit installation-os)
     (kernel linux)
-    (firmware (list linux-firmware))))
+    (firmware (list linux-firmware))
+    (skeletons
+      (cons ; add "channels.scm" to the "~/.config/guix" folder
+       `(".config" ,(file-union "guix"
+                                `(("guix/channels.scm" ,%channels-file))))
+        (operating-system-skeletons installation-os)))))
 
 installation-os-nonfree