build: Use "%D%" in Makefile fragments.

* doc/local.mk: Use "%D%" for the directory of the fragment relative to
the base 'Makefile.am'.
* emacs/local.mk: Likewise.
* gnu/local.mk: Likewise.
* nix/local.mk: Likewise.

Merge branch 'master' into gnome-updates

emacs: Add 'guix-package-from-file' command.

* emacs/guix-main.scm (register-package, packages-from-file): New procedures.
(%patterns-makers): Add 'from-file' search type.
* emacs/guix-messages.el (guix-messages): Add messages for it.
* emacs/guix-ui-package.el (guix-package-from-file): New command.
(guix-package-info-insert-location): Adjust for 'from-file' type.
* doc/emacs.texi (Emacs Commands): Document it.

emacs: main: Remove top-level package tables.

* emacs/guix-main.scm (%package-vhash, package-vhash, %package-table)
(package-table, name+version->key, key->name+version): Remove.
(package-by-address, packages-by-name+version): Adjust by using delayed
local package tables.

emacs: Simplify 'guix-guile-boolean'.

* emacs/guix-guile.el (guix-guile-boolean): Use straightforward way to
  define true/false value.

emacs: Add 'guix-version' command.

* emacs/guix-config.el.in (guix-config-name, guix-config-version): New
  constants.
* emacs/guix-about.el (guix-version): New command.  New file.
* emacs/local.mk (ELFILES): Add it.

Merge branch 'master' into gnome-updates

emacs: main: Use (guix combinators).

Reported by rsiddharth on #guix.
This is a followup to commit 958dd3ce68733bcd5c1231424c7e4ad39e67594a.

* emacs/guix-main.scm: Use (guix combinators) module as 'memoize' moved there.

emacs: Add "edit" command to a list of licenses.

* emacs/guix-ui-license.el (guix-license-list-edit): New command.
(guix-license-list-mode-map): Bind it to "e" key.

emacs: Add license definition button to License Info buffer.

* emacs/guix-ui-license.el (guix-license-insert-file): New procedure.
(guix-license-info-format): Use it.

emacs: Add 'guix-find-license-definition' command.

* emacs/guix-license.el (guix-license-file): New procedure.
(guix-find-license-definition): New command.
* doc/emacs.texi (Emacs Licenses): Document it.

build: Move 'Makefile' fragments to subdirectories.

This follows a convention used by some other GNU packages like Autoconf,
Bison, Coreutils, and Gnulib.

* doc.am: Rename to ...
* doc/local.mk: ... this.
* emacs.am: Rename to ...
* emacs/local.mk: ... this.
* gnu-system.am: Rename to ...
* gnu/local.mk: ... this.
* daemon.am: Rename to ...
* nix/local.mk: ... this.
* Makefile.am: Adapt to them.
* doc/guix.texi (Porting to a New Platform): Adapt documentation.
* guix/config.scm.in (%state-directory, %config-directory): Adapt comments.
* emacs/guix-config.el.in (guix-config-state-directory): Likewise.

emacs: Display license info on button press in Package Info buffer.

* emacs/guix-ui-package.el (guix-package-license): Adjust button action
  to display license info instead of browsing license URL.

emacs: Add location "Packages" button to Package Info buffer.

* emacs/guix-ui-package.el (guix-package-info-insert-location): New
procedure.
(guix-package-info-format): Use it.
(guix-output-info-format): Likewise.

emacs: Add interface for package locations.

* emacs/guix-main.scm (%package-location-param-alist): New variable.
(package-location->sexp, package-location-entries): New procedures.
* emacs/guix-ui-location.el: New file.
* emacs.am (ELFILES): Add it.
* doc/emacs.texi (Emacs Package Locations): Document 'guix-locations'.
* NEWS: Mention it.

emacs: Make 'guix-find-location' interactive.

* emacs/guix-location.el (guix-find-location): Make interactive.  Adjust
  to handle "reduced" locations (without line and column numbers).

emacs: Display message if license not found.

* emacs/guix-ui-license.el (guix-license-message): New procedure.
(guix-license-info-message-function): Use it.
(guix-license-list-message-function): Likewise.

emacs: Separate package license code.

Move list/info interface code from "guix-license.el" to
"guix-ui-license.el".

* emacs/guix-license.el (guix-license-get-entries, guix-license-get-display)
(guix-license-insert-packages-button, guix-license-insert-comment)
(guix-licenses): Move to...
* emacs/guix-ui-license.el: ... here.  New file.
* emacs.am (ELFILES): Add it.

emacs: Separate package location code.

* emacs/guix-base.el (guix-directory, guix-read-directory)
(guix-set-directory): Move to "guix-backend.el".
(guix-find-location, guix-package-location, guix-edit): Move to...
* emacs/guix-location.el: ... here.  New file.
* emacs/guix-ui-package.el: Use it.
* emacs.am (ELFILES): Add it.

emacs: Add 'guix-packages-by-location' command.

* emacs/guix-main.scm (packages-by-location-file, package-location-files):
New procedures.
(%patterns-makers): Add 'location' search type.
* emacs/guix-messages.el (guix-message-packages-by-location): New procedure.
(guix-messages): Use it.
* emacs/guix-read.el (guix-package-locations)
(guix-read-package-location): New procedures.
* emacs/guix-ui-package.el (guix-packages-by-location): New command.
* doc/emacs.texi (Emacs Commands): Document it.

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