build: Check for the availability of binaries upon "distcheck".

* build-aux/check-available-binaries.scm: New file.
* Makefile.am (EXTRA_DIST): Add it.
  (distcheck-hook, assert-binaries-available): New target.

Makefile.am

@@ -129,6 +129,7 @@ EXTRA_DIST =					\
   TODO						\
   .dir-locals.el				\
   build-aux/hydra/gnu-system.scm		\
+  build-aux/check-available-binaries.scm	\
   build-aux/download.scm			\
   build-aux/list-packages.scm			\
   build-aux/sync-synopses.scm			\
@@ -211,6 +212,7 @@ AM_DISTCHECK_CONFIGURE_FLAGS =			\
   --enable-daemon
 
 dist-hook: sync-synopses gen-ChangeLog assert-no-store-file-names
+distcheck-hook: assert-binaries-available
 
 sync-synopses:
 	-$(top_builddir)/pre-inst-env $(GUILE)		\
@@ -233,4 +235,10 @@ assert-no-store-file-names:
 	  exit 1 ;								\
 	fi
 
-.PHONY: sync-synopses gen-ChangeLog assert-no-store-file-names
+# Make sure hydra.gnu.org has the important binaries.
+assert-binaries-available:
+	$(top_builddir)/pre-inst-env "$(GUILE)"				\
+	  "$(top_srcdir)/build-aux/check-available-binaries.scm"
+
+.PHONY: sync-synopses gen-ChangeLog
+.PHONY: assert-no-store-file-names assert-binaries-available

build-aux/check-available-binaries.scm

@@ -0,0 +1,52 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2013 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/>.
+
+;;;
+;;; Check whether important binaries are available at hydra.gnu.org.
+;;;
+
+(use-modules (guix store)
+             (guix packages)
+             (guix derivations)
+             (gnu packages emacs)
+             (gnu packages make-bootstrap)
+             (srfi srfi-1)
+             (srfi srfi-26))
+
+(let* ((store  (open-connection))
+       (native (map (cut package-derivation store <>)
+                    (list %bootstrap-tarballs emacs)))
+       (cross  (map (cut package-cross-derivation store
+                         %bootstrap-tarballs <>)
+                    '("mips64el-linux-gnuabi64")))
+       (total  (append native cross)))
+  (define (warn proc)
+    (lambda (drv)
+      (or (proc drv)
+          (begin
+            (format (current-error-port) "~a is not substitutable~%"
+                    drv)
+            #f))))
+
+  (let ((result (every (compose (warn (cut has-substitutes? store <>))
+                                derivation-path->output-path)
+                       total)))
+    (when result
+      (format (current-error-port) "~a packages found substitutable~%"
+              (length total)))
+    (exit result)))