[bug#29409] [PATCH v2 3/4] scripts: system: Add --expression option.

[m.othacehe@gmail.com]

From: Mathieu Othacehe <m.othacehe@gmail.com>

* guix/scripts/system.scm (show-help): Add expression option.
(%options): Ditto.
(process-action): Read operating-system from expression or file.
* Makefile.am (release): Use expression instead of file to produce
disk-images.
* doc/guix.texi (Building the Installation Image): Adapt disk-image command to
  use an expression.
(Invoking guix system): Introduce the expression option.
---
 Makefile.am             |  2 +-
 doc/guix.texi           | 10 +++++++++-
 guix/scripts/system.scm | 24 +++++++++++++++++++-----
 3 files changed, 29 insertions(+), 7 deletions(-)

diff --git a/Makefile.am b/Makefile.am
index 85b9ab3..dff1e5e 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -648,7 +648,7 @@ release: dist
 	    guix system disk-image							\
 	    --file-system-type=iso9660							\
             --system=$$system								\
-	    gnu/system/install.scm` ;							\
+	    -e "(@ (gnu system install) installation-os)"` ;							\
 	  if [ ! -f "$$image" ] ; then							\
 	    echo "failed to produced GuixSD installation image for $$system" >&2 ;	\
 	    exit 1 ;									\
diff --git a/doc/guix.texi b/doc/guix.texi
index 92ac45b..9bdfdf7 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -8356,7 +8356,7 @@ The installation image described above was built using the @command{guix
 system} command, specifically:
 
 @example
-guix system disk-image gnu/system/install.scm
+guix system disk-image -e "(@@ (gnu system install) installation-os)"
 @end example
 
 Have a look at @file{gnu/system/install.scm} in the source tree,
@@ -18744,6 +18744,14 @@ Build Options}).  In addition, @var{options} can contain one of the
 following:
 
 @table @option
+@item --expression=@var{expr}
+@itemx -e @var{expr}
+Consider the operating-system @var{expr} evaluates to.
+This is an alternative to specifying a file which evaluates to an
+operating-system.
+This is used to generate the GuixSD installer @pxref{Building the
+Installation Image}).
+
 @item --system=@var{system}
 @itemx -s @var{system}
 Attempt to build for @var{system} instead of the host system type.
diff --git a/guix/scripts/system.scm b/guix/scripts/system.scm
index cbf7e6c..f710db9 100644
--- a/guix/scripts/system.scm
+++ b/guix/scripts/system.scm
@@ -858,6 +858,9 @@ Some ACTIONS support additional ARGS.\n"))
   (display (G_ "
   -d, --derivation       return the derivation of the given system"))
   (display (G_ "
+  -e, --expression=EXPR  consider the operating-system EXPR evaluates to
+                         instead of reading FILE, when applicable"))
+  (display (G_ "
       --on-error=STRATEGY
                          apply STRATEGY when an error occurs while reading FILE"))
   (display (G_ "
@@ -895,6 +898,9 @@ Some ACTIONS support additional ARGS.\n"))
          (option '(#\V "version") #f #f
                  (lambda args
                    (show-version-and-exit "guix system")))
+         (option '(#\e "expression") #t #f
+                 (lambda (opt name arg result)
+                   (alist-cons 'expression arg result)))
          (option '(#\d "derivation") #f #f
                  (lambda (opt name arg result)
                    (alist-cons 'derivations-only? #t result)))
@@ -964,11 +970,19 @@ resulting from command-line parsing."
   (let* ((file        (match args
                         (() #f)
                         ((x . _) x)))
+         (expr        (assoc-ref opts 'expression))
          (system      (assoc-ref opts 'system))
-         (os          (if file
-                          (load* file %user-module
-                                 #:on-error (assoc-ref opts 'on-error))
-                          (leave (G_ "no configuration file specified~%"))))
+         (os          (cond
+                       ((and expr file)
+                        (leave
+                         (G_ "both file and expression cannot be specified~%")))
+                       (expr
+                        (read/eval expr))
+                       (file
+                        (load* file %user-module
+                                    #:on-error (assoc-ref opts 'on-error)))
+                       (else
+                        (leave (G_ "no configuration specified~%")))))
 
          (dry?        (assoc-ref opts 'dry-run?))
          (bootloader? (assoc-ref opts 'install-bootloader?))
@@ -1093,7 +1107,7 @@ argument list and OPTS is the option alist."
 
       (case action
         ((build container vm vm-image disk-image reconfigure)
-         (unless (= count 1)
+         (unless (or (= count 1) (= count 0))
            (fail)))
         ((init)
          (unless (= count 2)
-- 
2.7.4