Add (guix bzr-download).

* guix/bzr-download.scm, guix/build/bzr.scm,
etc/snippets/scheme-mode/guix-bzr-reference: New files.
* Makefile.am (MODULES): Add them.
* etc/snippets/scheme-mode/guix-origin: Add "bzr-fetch" to the origin choices.

Makefile.am

@@ -78,6 +78,7 @@ MODULES =					\
   guix/modules.scm				\
   guix/download.scm				\
   guix/discovery.scm				\
+  guix/bzr-download.scm            		\
   guix/git-download.scm				\
   guix/hg-download.scm				\
   guix/swh.scm					\
@@ -160,6 +161,7 @@ MODULES =					\
   guix/build/font-build-system.scm		\
   guix/build/go-build-system.scm		\
   guix/build/asdf-build-system.scm		\
+  guix/build/bzr.scm				\
   guix/build/git.scm				\
   guix/build/hg.scm				\
   guix/build/glib-or-gtk-build-system.scm	\

etc/snippets/scheme-mode/guix-bzr-reference

@@ -0,0 +1,7 @@
+# -*- mode: snippet -*-
+# name: guix-bzr-reference
+# key: bzr-reference...
+# --
+(bzr-reference
+  (url "$1")
+  (revision ${2:ref}))

etc/snippets/scheme-mode/guix-origin

@@ -9,15 +9,17 @@
                                  "cvs-fetch"
                                  "git-fetch"
                                  "hg-fetch"
-                                 "svn-fetch")})
+                                 "svn-fetch"
+                                 "bzr-fetch")})
  (uri ${1:$(cond ((equal yas-text "git-fetch") "git-reference...")
                  ((equal yas-text "svn-fetch") "svn-reference...")
                  ((equal yas-text "hg-fetch")  "hg-reference...")
                  ((equal yas-text "cvs-fetch") "cvs-reference...")
+                 ((equal yas-text "bzr-fetch") "bzr-reference...")
                  (t "(string-append \\"https://\\" version \\".tar.gz\\")"))}$0)
  ${1:$(cond ((equal yas-text "git-fetch")
              "(file-name (git-file-name name version))")
-            ((member yas-text '("svn-fetch" "hg-fetch" "cvs-fetch"))
+            ((member yas-text '("svn-fetch" "hg-fetch" "cvs-fetch" "bzr-fetch"))
              "(file-name (string-append name \\"-\\" version \\"-checkout\\"))")
             (t ""))}
  (sha256

guix/build/bzr.scm

@@ -0,0 +1,44 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2018 Maxim Cournoyer <maxim.cournoyer@gmail.com>
+;;;
+;;; 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 build bzr)
+  #:use-module (guix build utils)
+  #:export (bzr-fetch))
+
+;;; Commentary:
+;;;
+;;; This is the build-side support code of (guix bzr-download).  It allows a
+;;; Bazaar repository to be branched at a specific revision.
+;;;
+;;; Code:
+
+(define* (bzr-fetch url revision directory
+                    #:key (bzr-command "bzr"))
+  "Fetch REVISION from URL into DIRECTORY.  REVISION must be a valid Bazaar
+revision identifier.  Return #t on success, else throw an exception."
+  ;; Do not attempt to write .bzr.log to $HOME, which doesn't exist.
+  (setenv "BZR_LOG" "/dev/null")
+  ;; Disable SSL certificate verification; we rely on the hash instead.
+  (invoke bzr-command "-Ossl.cert_reqs=none" "checkout"
+          "--lightweight" "-r" revision url directory)
+  (with-directory-excursion directory
+    (begin
+      (delete-file-recursively ".bzr")
+      #t)))
+
+;;; bzr.scm ends here

guix/bzr-download.scm

@@ -0,0 +1,85 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2017 Maxim Cournoyer <maxim.cournoyer@gmail.com>
+;;;
+;;; 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 bzr-download)
+  #:use-module (guix gexp)
+  #:use-module (guix modules)   ;for 'source-module-closure'
+  #:use-module (guix monads)
+  #:use-module (guix packages)
+  #:use-module (guix records)
+  #:use-module (guix store)
+
+  #:export (bzr-reference
+            bzr-reference?
+            bzr-reference-url
+            bzr-reference-revision
+
+            bzr-fetch))
+
+;;; Commentary:
+;;;
+;;; An <origin> method that fetches a specific revision from a Bazaar
+;;; repository.  The repository URL and revision identifier are specified with
+;;; a <bzr-reference> object.
+;;;
+;;; Code:
+
+(define-record-type* <bzr-reference>
+  bzr-reference make-bzr-reference
+  bzr-reference?
+  (url bzr-reference-url)
+  (revision bzr-reference-revision))
+
+(define (bzr-package)
+  "Return the default Bazaar package."
+  (let ((distro (resolve-interface '(gnu packages version-control))))
+    (module-ref distro 'bazaar)))
+
+(define* (bzr-fetch ref hash-algo hash
+                       #:optional name
+                       #:key (system (%current-system)) (guile (default-guile))
+                       (bzr (bzr-package)))
+  "Return a fixed-output derivation that fetches REF, a <bzr-reference>
+object.  The output is expected to have recursive hash HASH of type
+HASH-ALGO (a symbol).  Use NAME as the file name, or a generic name if #f."
+  (define build
+    (with-imported-modules (source-module-closure
+                            '((guix build bzr)))
+      #~(begin
+          (use-modules (guix build bzr))
+          (bzr-fetch
+           (getenv "bzr url") (getenv "bzr reference") #$output
+           #:bzr-command (string-append #+bzr "/bin/bzr")))))
+
+  (mlet %store-monad ((guile (package->derivation guile system)))
+    (gexp->derivation (or name "bzr-branch") build
+                      ;; Use environment variables and a fixed script name so
+                      ;; there's only one script in store for all the
+                      ;; downloads.
+                      #:script-name "bzr-download"
+                      #:env-vars
+                      `(("bzr url" . ,(bzr-reference-url ref))
+                        ("bzr reference" . ,(bzr-reference-revision ref)))
+                      #:system system
+                      #:local-build? #t  ;don't offload repo branching
+                      #:hash-algo hash-algo
+                      #:hash hash
+                      #:recursive? #t
+                      #:guile-for-build guile)))
+
+;;; bzr-download.scm ends here