installer: Set the system's 'keyboard-layout' field.

* gnu/installer/newt/keymap.scm (keyboard-layout->configuration): New
procedure.
* gnu/installer.scm (compute-keymap-step): Return RESULT.
(installer-steps) <'keymap>: Add 'configuration-formatter' field.
(installer-program): Use (gnu installer newt keymap).
* gnu/installer/parted.scm (bootloader-configuration): Set
'keyboard-layout'.

gnu/installer.scm

@@ -1,5 +1,6 @@
 ;;; GNU Guix --- Functional package management for GNU
 ;;; Copyright © 2018 Mathieu Othacehe <m.othacehe@gmail.com>
+;;; Copyright © 2019 Ludovic Courtès <ludo@gnu.org>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -156,7 +157,8 @@ selected keymap."
                (lambda (models layouts)
                  ((installer-keymap-page current-installer)
                   layouts)))))
-        (#$apply-keymap result))))
+        (#$apply-keymap result)
+        result)))
 
 (define (installer-steps)
   (let ((locale-step (compute-locale-step
@@ -208,7 +210,8 @@ selected keymap."
           (id 'keymap)
           (description (G_ "Keyboard mapping selection"))
           (compute (lambda _
-                     (#$keymap-step current-installer))))
+                     (#$keymap-step current-installer)))
+          (configuration-formatter keyboard-layout->configuration))
 
          ;; Run a partitioning tool allowing the user to modify
          ;; partition tables, partitions and their mount points.
@@ -313,6 +316,8 @@ selected keymap."
                          (gnu installer timezone)
                          (gnu installer user)
                          (gnu installer newt)
+                         ((gnu installer newt keymap)
+                          #:select (keyboard-layout->configuration))
                          (guix i18n)
                          (guix build utils)
                          (ice-9 match))

gnu/installer/newt/keymap.scm

@@ -1,5 +1,6 @@
 ;;; GNU Guix --- Functional package management for GNU
 ;;; Copyright © 2018 Mathieu Othacehe <m.othacehe@gmail.com>
+;;; Copyright © 2019 Ludovic Courtès <ludo@gnu.org>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -27,7 +28,9 @@
   #:use-module (srfi srfi-26)
   #:use-module (srfi srfi-34)
   #:use-module (srfi srfi-35)
-  #:export (run-keymap-page))
+  #:use-module (ice-9 match)
+  #:export (run-keymap-page
+            keyboard-layout->configuration))
 
 (define (run-layout-page layouts layout->text)
   (let ((title (G_ "Layout")))
@@ -120,3 +123,11 @@ names of the selected keyboard layout and variant."
       (list layout (or variant ""))))
   (format-result
    (run-installer-steps #:steps keymap-steps)))
+
+(define (keyboard-layout->configuration keymap)
+  "Return the operating system configuration snippet to install KEYMAP."
+  (match keymap
+    ((name "")
+     `((keyboard-layout (keyboard-layout ,name))))
+    ((name variant)
+     `((keyboard-layout (keyboard-layout ,name ,variant))))))

gnu/installer/parted.scm

@@ -1258,7 +1258,11 @@ from (gnu system mapped-devices) and return it."
              `((bootloader grub-efi-bootloader)
                (target ,(default-esp-mount-point)))
              `((bootloader grub-bootloader)
-               (target ,root-partition-disk)))))))
+               (target ,root-partition-disk)))
+
+       ;; XXX: Assume we defined the 'keyboard-layout' field of
+       ;; <operating-system> right above.
+       (keyboard-layout keyboard-layout)))))
 
 (define (user-partitions->configuration user-partitions)
   "Return the configuration field for USER-PARTITIONS."