doc: Use @deftp for 'build-machine'.

* doc/guix.texi (Daemon Offload Setup): Use @deftp for 'build-machine'.

daemon: Add '--substitute-urls' option.

* nix/nix-daemon/guix-daemon.cc (GUIX_OPT_SUBSTITUTE_URLS): New macro.
  (GUIX_OPT_NO_BUILD_HOOK, GUIX_OPT_GC_KEEP_OUTPUTS,
  GUIX_OPT_GC_KEEP_DERIVATIONS): Renumber.
  (options): Add '--substitute-urls'.
  (parse_opt): Honor it.
  (main): Add 'settings.set' call for the default "substitute-urls"
  value.
* guix/scripts/substitute-binary.scm (daemon-options,
  find-daemon-option): New procedures.
  (%cache-url): Define based on the "substitute-urls" daemon option.
* doc/guix.texi (Invoking guix-daemon): Document '--substitute-urls'.
  (Substitutes): Mention it.

monads: Add 'mbegin'.

* guix/monads.scm (mbegin): New macro.
* tests/monads.scm ("mbegin"): New test.
* doc/guix.texi (The Store Monad): Document it.

doc: Document 'glib-or-gtk-build-system'.

* doc/guix.texi (Build System): Document 'glib-or-gtk-build-system'.

Co-authored-by: Ludovic Courtès <ludo@gnu.org>

services: Add '%facebook-host-aliases'.

* gnu/services/networking.scm (%facebook-host-aliases): New variable.
* doc/guix.texi (Networking Services): Document it.

doc: Mention optional dependency on Guile-JSON.

* README (Requirements): Add Guile-JSON.
* doc/guix.texi (Requirements): Likewise.

emacs: Add support for deleting generations.

* doc/emacs.texi (emacs List buffer): Mention new key bindings.
* emacs/guix-base.el (guix-delete-generations): New procedure.
* emacs/guix-info.el (guix-generation-info-insert-number): Use it.
* emacs/guix-list.el (guix-generation-list-mark-delete,
  guix-generation-list-execute): New procedures.
* emacs/guix-main.scm (delete-generations*): New procedure.

build-system: Introduce "bags" as an intermediate representation.

* guix/build-system.scm (<build-system>)[build, cross-build]: Remove.
  [lower]: New field.
  (<bag>): New record type.
  (make-bag): New procedure.
* guix/packages.scm (bag-transitive-inputs, bag-transitive-build-inputs,
  bag-transitive-host-inputs, bag-transitive-target-inputs,
  package->bag): New procedures.
  (package-derivation): Use it; use the bag, apply its build procedure,
  etc.
  (package-cross-derivation): Likewise.
* gnu/packages/bootstrap.scm (raw-build, make-raw-bag): New procedure.
  (%bootstrap-guile): Use them.
* guix/build-system/trivial.scm (lower): New procedure.
  (trivial-build, trivial-cross-build): Remove 'source' parameter.  Pass
  INPUTS as is.
  (trivial-build-system): Adjust accordingly.
* guix/build-system/gnu.scm (%store, inputs-search-paths,
  standard-search-paths, expand-inputs, standard-inputs): Remove.
  (gnu-lower): New procedure.
  (gnu-build): Remove 'source' and #:implicit-inputs? parameters.
  Remove 'implicit-inputs' and 'implicit-search-paths' variables.  Get
  the source from INPUT-DRVS.
  (gnu-cross-build): Likewise.
  (standard-cross-packages): Remove call to 'standard-packages'.
  (standard-cross-inputs, standard-cross-search-paths): Remove.
  (gnu-build-system): Remove 'build' and 'cross-build'; add 'lower'.
* guix/build-system/cmake.scm (lower): New procedure.
  (cmake-build): Remove 'source' and #:cmake parameters.  Use INPUTS and
  SEARCH-PATHS as is.  Get the source from INPUTS.
* guix/build-system/perl.scm: Likewise.
* guix/build-system/python.scm: Likewise.
* guix/build-system/ruby.scm: Likewise.
* gnu/packages/cross-base.scm (cross-gcc): Change "cross-linux-headers"
  to "linux-headers".
  (cross-libc)[xlinux-headers]: Pass #:implicit-cross-inputs? #f.
  Likewise.  In 'propagated-inputs', change "cross-linux-headers" to
  "linux-headers".
* guix/git-download.scm (git-fetch): Use 'standard-packages' instead of
  'standard-inputs'.
* tests/builders.scm ("gnu-build-system"): Remove use of
  'build-system-builder'.
  ("gnu-build"): Remove 'source' and #:implicit-inputs? arguments to
  'gnu-build'.
* tests/packages.scm ("search paths"): Adjust to new build system API.
  ("package-cross-derivation, no cross builder"): Likewise.
* doc/guix.texi (Build Systems): Add paragraph on bags.

build-system/cmake: Add #:build-type parameter, default to "RelWithDebInfo".

* guix/build-system/cmake.scm (cmake-build): Add #:build-type.  Pass it
  in BUILDER.
* guix/build/cmake-build-system.scm (configure): Add #:build-type
  parameter and honor it.
* doc/guix.texi (Build Systems): Document #:configure-flags and
  #:build-type for CMake.

ui: Recognize the same size units as Coreutils.

* guix/ui.scm (size->number): Add a bunch of large units.  Recognize
  one-letter unit names.  Change "KB" to "kB".
* tests/ui.scm ("size->number, 1T"): New test.
* doc/guix.texi (Invoking guix gc): Add cross-reference to "Block size"
  in the Coreutils manual.
  (Invoking guix system): Likewise.

build: Add ruby build system.

* guix/build-system/ruby.scm: New file.
* guix/build/ruby-build-system: New file.
* Makefile.am (MODULES): Add new files.
* doc/guix.texi (Build Systems): Document ruby-build-system.

doc: Use 'define-public' in example package recipe.

* doc/guix.texi (Defining Packages): Use 'define-public' instead of
  'define'.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>

emacs: Add support for displaying outputs.

Suggested by Taylan Ulrich Bayirli/Kammer and Ludovic Courtès.

* emacs/guix-base.el (guix-param-titles): Add output titles.
  (guix-messages): Add output messages.
  (guix-get-package-id-and-output-by-output-id): New procedure.
  (guix-define-buffer-type): Add ':buffer-name' key.
* emacs/guix-info.el: Add "output-info" buffer type.
  (guix-info-insert-methods): Add output methods.
  (guix-info-displayed-params): Add output params.
  (guix-output-info-insert-version, guix-output-info-insert-output): New
  procedures.
* emacs/guix-list.el: Add "output-list" buffer type.
  (guix-list-column-format): Add output formats.
  (guix-list-column-value-methods): Add output methods.
  (guix-package-list-type): New variable.
  (guix-generation-list-show-packages): Use it.
  (guix-package-list-marking-check): Use 'guix-output-list-mode'.
  (guix-list-mark-package-upgrades): New procedure.
  (guix-package-list-mark-upgrades): Use it.
  (guix-list-execute-package-actions): New procedure.
  (guix-package-list-execute): Use it.
  (guix-list-describe-maybe): New procedure.
  (guix-list-describe): Use it.
  (guix-output-list-mark-install, guix-output-list-mark-delete,
  guix-output-list-mark-upgrade, guix-output-list-mark-upgrades,
  guix-output-list-execute, guix-output-list-make-action,
  guix-output-list-describe): New procedures.
  (guix-output-list-describe-type): New variable.
* emacs/guix.el (guix-get-show-packages): Use 'guix-package-list-type'.
* doc/emacs.texi (emacs Commands): Mention 'guix-package-list-type'.
  (emacs List buffer): Adjust accordingly.
  (emacs Info buffer): Likewise.
  (emacs Buffer Names): New node.
  (emacs Keymaps): Add keymaps for output buffers.

Introduce the 'GUIX_PACKAGE_PATH' environment variable.

* gnu/packages.scm (%package-module-path): Honor $GUIX_PACKAGE_PATH.
* test-env.in: Unset 'GUIX_PACKAGE_PATH'.
* tests/guix-package.sh: Test it.
* doc/guix.texi (Package Modules): Document it.

guix build: Add -L/--load-path as a common option.

* guix/scripts/build.scm (show-build-options-help): Document -L.
  (%standard-build-options): Add -L/--load-path.
* tests/guix-package.sh: Test it.

services: Add 'bitlbee-service'.

* gnu/services/networking.scm (bitlbee-service): New procedure.
* doc/guix.texi (Networking Services): Document it.

linux-initrd: Adjust VM code and doc to new 'base-initrd' signature.

This fixes regressions introduced in de1c158 ("system: Add support for
boot-time mapped devices.").

* doc/guix.texi (Initial RAM Disk): Adjust example with custom use of
  'base-initrd'.  Document #:mapped-devices parameter of 'base-initrd'.
* gnu/system/vm.scm (system-disk-image, system-qemu-image,
  virtualized-operating-system): Adjust call to 'base-initrd' to new
  signature.

doc: Remove a couple of limitations.

* doc/guix.texi (System Installation): Remove encrypted disks and swap
  from the limitations.

doc: Document mapped devices.

* doc/guix.texi (Mapped Devices): New subsection.

services: Add 'dhcp-client-service'.

* gnu/services/networking.scm (dhcp-client-service): New procedure.
* doc/guix.texi (Networking Services): Document it.