style: Add '--whole-file' option.

* guix/scripts/style.scm (format-whole-file): New procedure.
(%options, show-help): Add '--whole-file'.
(guix-style): Honor it.
* tests/guix-style.sh: New file.
* Makefile.am (SH_TESTS): Add it.
* doc/guix.texi (Invoking guix style): Document it.

tests/guix-style.sh

@@ -0,0 +1,80 @@
+# GNU Guix --- Functional package management for GNU
+# Copyright © 2022 Ludovic Courtès <ludo@gnu.org>
+#
+# This file is part of GNU Guix.
+#
+# GNU Guix is free software; you can redistribute it and/or modify it
+# under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or (at
+# your option) any later version.
+#
+# GNU Guix is distributed in the hope that it will be useful, but
+# WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.
+
+#
+# Test 'guix style'.
+#
+
+set -e
+
+guix style --version
+
+tmpdir="guix-style-$$"
+trap 'rm -r "$tmpdir"' EXIT
+
+tmpfile="$tmpdir/os.scm"
+mkdir "$tmpdir"
+cat > "$tmpfile" <<EOF
+;;; This is a header with three semicolons.
+;;;
+
+(define-module (foo bar)
+  #:use-module (guix)
+  #:use-module (gnu))
+
+;; One blank line and a page break.
+
+
+;; And now, the OS.
+(operating-system
+  (host-name "komputilo")
+  (locale "eo_EO.UTF-8")
+
+  ;; User accounts.
+  (users (cons (user-account
+                 (name "alice")
+                 (comment "Bob's sister")
+                 (group "users")
+
+                 ;; Groups fit on one line.
+                 (supplementary-groups '("wheel" "audio" "video")))
+               %base-user-accounts))
+
+  ;; The services.
+  (services
+   (cons (service mcron-service-type) %base-services)))
+EOF
+
+cp "$tmpfile" "$tmpfile.bak"
+
+initial_hash="$(guix hash "$tmpfile")"
+
+guix style -f "$tmpfile"
+if ! test "$initial_hash" = "$(guix hash "$tmpfile")"
+then
+    cat "$tmpfile"
+    diff -u "$tmpfile.bak" "$tmpfile"
+    false
+fi
+
+# Introduce random changes and try again.
+sed -i "$tmpfile" -e's/ +/ /g'
+! test "$initial_hash" = "$(guix hash "$tmpfile")"
+
+guix style -f "$tmpfile"
+test "$initial_hash" = "$(guix hash "$tmpfile")"