Add 'guix describe'.

* guix/scripts/describe.scm: New file.
* Makefile.am (MODULES): Add it.
(SH_TESTS): Add tests/guix-describe.sh.
* po/guix/POTFILES.in: Add it.
* guix/scripts/pull.scm (display-profile-content): Export.
* guix/describe.scm (current-profile, current-profile-entries): Export.
* tests/guix-describe.sh: New file.
* doc/guix.texi (Features): Mention 'guix pull' and provenance tracking.
(Invoking guix pull): Link to 'guix describe'.
(Channels): Likewise.
(Invoking guix describe): New node.

3 files changed, 165 insertions, 2 deletions

diff --git a/guix/describe.scm b/guix/describe.scm
index 3122a762fe..670db63ce7 100644
--- a/guix/describe.scm
+++ b/guix/describe.scm
@@ -21,7 +21,9 @@
   #:use-module (guix profiles)
   #:use-module (srfi srfi-1)
   #:use-module (ice-9 match)
-  #:export (package-path-entries))
+  #:export (current-profile
+            current-profile-entries
+            package-path-entries))
 
 ;;; Commentary:
 ;;;
diff --git a/guix/scripts/describe.scm b/guix/scripts/describe.scm
new file mode 100644
index 0000000000..46feea2940
--- /dev/null
+++ b/guix/scripts/describe.scm
@@ -0,0 +1,160 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2018 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/>.
+
+(define-module (guix scripts describe)
+  #:use-module ((guix ui) #:hide (display-profile-content))
+  #:use-module (guix scripts)
+  #:use-module (guix describe)
+  #:use-module (guix profiles)
+  #:use-module ((guix scripts pull) #:select (display-profile-content))
+  #:use-module (git)
+  #:use-module (srfi srfi-1)
+  #:use-module (srfi srfi-37)
+  #:use-module (ice-9 match)
+  #:autoload   (ice-9 pretty-print) (pretty-print)
+  #:export (guix-describe))
+
+
+;;;
+;;; Command-line options.
+;;;
+
+(define %options
+  ;; Specifications of the command-line options.
+  (list (option '(#\f "format") #t #f
+                (lambda (opt name arg result)
+                  (unless (member arg '("human" "channels"))
+                    (leave (G_ "~a: unsupported output format~%") arg))
+                  (alist-cons 'format 'channels result)))
+        (option '(#\h "help") #f #f
+                (lambda args
+                  (show-help)
+                  (exit 0)))
+        (option '(#\V "version") #f #f
+                (lambda args
+                  (show-version-and-exit "guix describe")))))
+
+(define %default-options
+  ;; Alist of default option values.
+  '((format . human)))
+
+(define (show-help)
+  (display (G_ "Usage: guix describe [OPTION]...
+Display information about the channels currently in use.\n"))
+  (display (G_ "
+  -f, --format=FORMAT    display information in the given FORMAT"))
+  (newline)
+  (display (G_ "
+  -h, --help             display this help and exit"))
+  (display (G_ "
+  -V, --version          display version information and exit"))
+  (newline)
+  (show-bug-report-information))
+
+(define (display-package-search-path fmt)
+  "Display GUIX_PACKAGE_PATH, if it is set, according to FMT."
+  (match (getenv "GUIX_PACKAGE_PATH")
+    (#f #t)
+    (string
+     (match fmt
+       ('human
+        (format #t "~%GUIX_PACKAGE_PATH=\"~a\"~%" string))
+       ('channels
+        (format #t (G_ "~%;; warning: GUIX_PACKAGE_PATH=\"~a\"~%")
+                string))))))
+
+(define (display-checkout-info fmt)
+  "Display information about the current checkout according to FMT, a symbol
+denoting the requested format.  Exit if the current directory does not lie
+within a Git checkout."
+  (let* ((program    (car (command-line)))
+         (directory  (catch 'git-error
+                       (lambda ()
+                         (repository-discover (dirname program)))
+                       (lambda (key err)
+                         (leave (G_ "failed to determine origin~%")))))
+         (repository (repository-open directory))
+         (head       (repository-head repository))
+         (commit     (oid->string (reference-target head))))
+    (match fmt
+      ('human
+       (format #t (G_ "Git checkout:~%"))
+       (format #t (G_ "  repository: ~a~%") (dirname directory))
+       (format #t (G_ "  branch: ~a~%") (reference-shorthand head))
+       (format #t (G_ "  commit: ~a~%") commit))
+      ('channels
+       (pretty-print `(list (channel
+                             (name 'guix)
+                             (url ,(dirname directory))
+                             (commit ,commit))))))
+    (display-package-search-path fmt)))
+
+(define (display-profile-info profile fmt)
+  "Display information about PROFILE, a profile as created by (guix channels),
+in the format specified by FMT."
+  (define number
+    (match (profile-generations profile)
+      ((_ ... last) last)))
+
+  (match fmt
+    ('human
+     (display-profile-content profile number))
+    ('channels
+     (pretty-print
+      `(list ,@(map (lambda (entry)
+                      (match (assq 'source (manifest-entry-properties entry))
+                        (('source ('repository ('version 0)
+                                               ('url url)
+                                               ('branch branch)
+                                               ('commit commit)
+                                               _ ...))
+                         `(channel (name ',(string->symbol
+                                            (manifest-entry-name entry)))
+                                   (url ,url)
+                                   (commit ,commit)))
+
+                        ;; Pre-0.15.0 Guix does not provide that information,
+                        ;; so there's not much we can do in that case.
+                        (_ '???)))
+
+                    ;; Show most recently installed packages last.
+                    (reverse
+                     (manifest-entries
+                      (profile-manifest (generation-file-name profile
+                                                              number)))))))))
+  (display-package-search-path fmt))
+
+
+;;;
+;;; Entry point.
+;;;
+
+(define (guix-describe . args)
+  (let* ((opts   (args-fold* args %options
+                             (lambda (opt name arg result)
+                               (leave (G_ "~A: unrecognized option~%")
+                                      name))
+                             cons
+                             %default-options))
+         (format (assq-ref opts 'format)))
+    (with-error-handling
+      (match (current-profile)
+        (#f
+         (display-checkout-info format))
+        (profile
+         (display-profile-info profile format))))))
diff --git a/guix/scripts/pull.scm b/guix/scripts/pull.scm
index ebc5dc9b13..976e054a84 100644
--- a/guix/scripts/pull.scm
+++ b/guix/scripts/pull.scm
@@ -48,7 +48,8 @@
   #:use-module (srfi srfi-37)
   #:use-module (ice-9 match)
   #:use-module (ice-9 vlist)
-  #:export (guix-pull))
+  #:export (display-profile-content
+            guix-pull))
 
 
 ;;;