guix system: Factorize 'copy-closure'.

* guix/scripts/system.scm (copy-closure): Rename to...
  (copy-item): ... this.
  (copy-closure): New procedure.
  (install): Use it, and remove redundant code.

guix system: init: Always use /var/guix as the target state directory.

Fixes <http://bugs.gnu.org/18049>.
Reported by Marek Benc <merkur32@gmail.com>.

* guix/scripts/system.scm (copy-closure): Pass #:state-directory to
  'register-path'.

guix system: reconfigure: Always use "/" as GRUB's target file system.

* guix/scripts/system.scm (perform-action) <reconfigure>: Wrap
  'install-grub' call in 'false-if-exception'.  Always use "/" as the
  target.

guix system: Fix return value for 'reconfigure'.

* guix/scripts/system.scm (perform-action) <reconfigure>: Add missing
  'return' expression.

guix system: Convert to monadic style.

* guix/scripts/system.scm (references*, topologically-sorted*,
  show-what-to-build*): New procedures.
  (copy-closure): Turn into a monadic procedure.
  (install): Likewise, and adjust parameter list.
  (switch-to-system): Likewise.
  (system-derivation-for-action, grub.cfg, maybe-build, perform-action):
  New procedures.
  (guix-system): Use them.

guix system: Add '--system' option.

* guix/scripts/system.scm (switch-to-system): Add #:system parameter;
  pass it to 'run-with-store'.
  (%options): Add '--system'.
  (guix-system): Pass the 'system' option to 'run-with-store',
  'package-derivation', and 'switch-to-system' calls.
* doc/guix.texi (Invoking guix system): Document '--system' and
  '--image-size'.

system: Install /var/guix/profiles/system-1-link on new systems.

* guix/build/install.scm (directives): Add /var/guix/profiles/system.
  (populate-root-file-system): Add 'system' parameter.  Create
  /var/guix/profiles/system-1-link.
* guix/scripts/system.scm (install): Pass OS-DIR to
  'populate-root-file-system'.
* guix/build/vm.scm (initialize-root-partition): Add #:system-directory
  parameter, and pass it to 'populate-root-file-system'.
  (initialize-hard-disk): Add #:system-directory parameter, and pass it
  to 'initialize-root-partition'.
* gnu/system/vm.scm (qemu-image): Add #:os-derivation parameter and pass
  it to 'initialize-hard-disk'.
  (system-disk-image, system-qemu-image,
  system-qemu-image/shared-store): Pass #:os-derivation to 'qemu-image.

guix system: Add 'reconfigure' action.

* guix/scripts/system.scm (%system-profile): New variable.
  (switch-to-system, previous-grub-entries): New procedures.
  (unless-file-not-found): New macro.
  (show-help): Add 'reconfigure'.
  (guix-system): Handle it.
* gnu/system.scm: Export 'operating-system-activation-script'.
* doc/guix.texi (Invoking guix system): Document it.

guix {system,offload}: Improve reporting of syntax errors.

* guix/scripts/system.scm (read-operating-system) <catch handler>: Add
  case for 'syntax-error'.  Correct message for default case.
* guix/scripts/offload.scm (build-machines) <catch handler>: Add case
  for 'syntax-error'.
* tests/guix-system.sh: New file.
* Makefile.am (SH_TESTS): Add it.

guix system: Gracefully handle 'install-grub' errors.

* guix/scripts/system.scm (install): Wrap 'install-grub' call in
  'false-if-exception'.  This is a followup to 641f9a2a.

Merge branch 'core-updates'

guix system: 'init' makes sure the target store directory exists.

* guix/scripts/system.scm (install): Before calling 'copy-closure', make
  sure directory (%store-prefix) under TARGET exists.

Merge branch 'master' into core-updates

guix system: Add 'disk-image' action.

* guix/scripts/system.scm (show-help): Add 'disk-image'.
  (guix-system)[parse-options]: Support 'disk-image' action.
  [option-arguments]: Likewise.
  Handle the 'disk-image' action.
* doc/guix.texi (Invoking guix system): Document 'disk-image'.

guix system: Check whether we are installing to /.

* guix/scripts/system.scm (install): Check whether TARGET is / and warn.

guix system: Factorize out closure copy.

* guix/scripts/system.scm (copy-closure): New procedure.
  (install): Use it.

guix system: 'guix system init' installs GRUB by default.

* guix/scripts/system.scm (install): Add #:grub?, #:grub.cfg, and
  #:device parameters; honor them.
  (show-help): Document '--no-grub'.
  (%options): Add '--no-grub'.
  (%default-options): Add 'install-grub?'.
  (guix-system): Honor 'install-grub?' option from OPTS.  Adjust
  'install' call accordingly.
* doc/guix.texi (Invoking guix system): Document '--no-grub'.

guix system: Add 'init' sub-command.

* guix/scripts/system.scm (install): New procedure.
  (guix-system)[parse-option]: Remove check for extraneous arguments.
  [match-pair, option-arguments]: New procedures.
  Use 'option-arguments'.  Honor 'init'.
  (show-help): Document 'init'.
* doc/guix.texi (Invoking guix system): Document 'init'.

guix system: Add 'build' action.

* guix/scripts/system.scm (show-help): Document 'build' action.
  (guix-system): Honor 'build' action.
* doc/guix.texi (Invoking guix system): Add 'build' action.

guix system: Add 'vm-image' action and '--image-size' option.

* guix/scripts/system.scm (%options): Add --image-size.
  (%default-options): Add 'image-size'.
  (guix-system)[parse-options]: Handle the 'vm-image' action.
  Honor them.
  (show-help): Update accordingly.
* doc/guix.texi (Invoking guix system): Add 'vm-image'.