The format of locale data can be incompatible between libc versions, and
loading incompatible data can lead to 'setlocale' returning EINVAL at best
or triggering an assertion failure at worst.  See
https://lists.gnu.org/archive/html/guix-devel/2015-09/msg00717.html
for background information.

To address that, this patch changes libc to honor a new 'GUIX_LOCPATH'
variable, and to look for locale data in version-specific sub-directories of
that variable.  So, if GUIX_LOCPATH=/foo:/bar, locale data is searched for in
/foo/X.Y and /bar/X.Y, where X.Y is the libc version number.

That way, a single 'GUIX_LOCPATH' setting can work even if different libc
versions coexist on the system.

diff --git a/locale/Makefile b/locale/Makefile
index d7036b08..b5125166 100644
--- a/locale/Makefile
+++ b/locale/Makefile
@@ -94,7 +94,9 @@ localepath = "$(complocaledir):$(i18ndir)"
 # -Iprograms doesn't really belong here, but this gets it at the head
 # of the list instead of the tail, where CPPFLAGS-$(lib) gets added.
 # We need it before the standard -I's to see programs/config.h first.
+# Define 'LOCALEDIR' for use in 'compute_locale_search_path'.
 locale-CPPFLAGS = -DCOMPLOCALEDIR='"$(complocaledir)"' \
+		  -DLOCALEDIR='"$(libdir)/locale"'     \
 		  -DLOCALE_ALIAS_PATH='"$(localedir)"' \
 		  -Iprograms
 
diff --git a/locale/newlocale.c b/locale/newlocale.c
index 108d2428..6218e0fa 100644
--- a/locale/newlocale.c
+++ b/locale/newlocale.c
@@ -29,6 +29,7 @@
 /* Lock for protecting global data.  */
 __libc_rwlock_define (extern , __libc_setlocale_lock attribute_hidden)
 
+extern error_t compute_locale_search_path (char **, size_t *);
 
 /* Use this when we come along an error.  */
 #define ERROR_RETURN							      \
@@ -47,7 +48,6 @@ __newlocale (int category_mask, const char *locale, locale_t base)
   locale_t result_ptr;
   char *locale_path;
   size_t locale_path_len;
-  const char *locpath_var;
   int cnt;
   size_t names_len;
 
@@ -101,17 +101,8 @@ __newlocale (int category_mask, const char *locale, locale_t base)
   locale_path = NULL;
   locale_path_len = 0;
 
-  locpath_var = getenv ("LOCPATH");
-  if (locpath_var != NULL && locpath_var[0] != '\0')
-    {
-      if (__argz_create_sep (locpath_var, ':',
-			     &locale_path, &locale_path_len) != 0)
-	return NULL;
-
-      if (__argz_add_sep (&locale_path, &locale_path_len,
-			  _nl_default_locale_path, ':') != 0)
-	return NULL;
-    }
+  if (compute_locale_search_path (&locale_path, &locale_path_len) != 0)
+    return NULL;
 
   /* Get the names for the locales we are interested in.  We either
      allow a composite name or a single name.  */
diff --git a/locale/setlocale.c b/locale/setlocale.c
index 6a902faa..2d07a644 100644
--- a/locale/setlocale.c
+++ b/locale/setlocale.c
@@ -213,12 +213,60 @@ setdata (int category, struct __locale_data *data)
     }
 }
 
+/* Return in *LOCALE_PATH and *LOCALE_PATH_LEN the locale data search path as
+   an argz list.  Return ENOMEN on error, zero otherwise.  */
+error_t
+compute_locale_search_path (char **locale_path, size_t *locale_path_len)
+{
+  char* guix_locpath_var = getenv ("GUIX_LOCPATH");
+  char *locpath_var = getenv ("LOCPATH");
+
+  if (guix_locpath_var != NULL && guix_locpath_var[0] != '\0')
+    {
+      /* Entries in 'GUIX_LOCPATH' take precedence over 'LOCPATH'.  These
+	 entries are systematically prefixed with "/X.Y" where "X.Y" is the
+	 libc version.  */
+      if (__argz_add_sep (locale_path, locale_path_len,
+                          guix_locpath_var, ':') != 0
+	  || __argz_suffix_entries (locale_path, locale_path_len,
+				    "/" VERSION) != 0)
+	goto bail_out;
+    }
+
+  if (locpath_var != NULL && locpath_var[0] != '\0')
+    {
+      if (__argz_add_sep (locale_path, locale_path_len,
+			   locpath_var, ':') != 0)
+	goto bail_out;
+
+    }
+
+  /* Append the system default locale directory.  */
+  if (__argz_add_sep (locale_path, locale_path_len,
+   		       _nl_default_locale_path, ':') != 0)
+    goto bail_out;
+
+  /* Last, unconditionally append our own locale directory, which should
+     contain data for C.UTF-8.  */
+  if (__argz_add_sep (locale_path, locale_path_len,
+		       LOCALEDIR "/" VERSION, ':') != 0)
+    goto bail_out;
+
+  return 0;
+
+ bail_out:
+  free (*locale_path);
+  *locale_path = NULL;
+  *locale_path_len = 0;
+
+  return ENOMEM;
+}
+
 char *
 setlocale (int category, const char *locale)
 {
   char *locale_path;
   size_t locale_path_len;
-  const char *locpath_var;
   char *composite;
 
   /* Sanity check for CATEGORY argument.  */
@@ -249,17 +308,10 @@ setlocale (int category, const char *locale)
   locale_path = NULL;
   locale_path_len = 0;
 
-  locpath_var = getenv ("LOCPATH");
-  if (locpath_var != NULL && locpath_var[0] != '\0')
+  if (compute_locale_search_path (&locale_path, &locale_path_len) != 0)
     {
-      if (__argz_create_sep (locpath_var, ':',
-			     &locale_path, &locale_path_len) != 0
-	  || __argz_add_sep (&locale_path, &locale_path_len,
-			     _nl_default_locale_path, ':') != 0)
-	{
-	  __libc_rwlock_unlock (__libc_setlocale_lock);
-	  return NULL;
-	}
+      __libc_rwlock_unlock (__libc_setlocale_lock);
+      return NULL;
     }
 
   if (category == LC_ALL)
diff --git a/string/Makefile b/string/Makefile
index 8cdfd5b0..6b0d606d 100644
--- a/string/Makefile
+++ b/string/Makefile
@@ -51,6 +51,7 @@ routines := \
   argz-next \
   argz-replace \
   argz-stringify \
+  argz-suffix \
   basename \
   bcopy \
   bzero \
diff --git a/string/argz-suffix.c b/string/argz-suffix.c
new file mode 100644
index 00000000..505b0f24
--- /dev/null
+++ b/string/argz-suffix.c
@@ -0,0 +1,58 @@
+/* Copyright (C) 2015 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+   Contributed by Ludovic Courtès <ludo@gnu.org>.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library 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
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <argz.h>
+#include <errno.h>
+#include <stdlib.h>
+#include <string.h>
+
+
+error_t
+__argz_suffix_entries (char **argz, size_t *argz_len, const char *suffix)
+
+{
+  size_t suffix_len = strlen (suffix);
+  size_t count = __argz_count (*argz, *argz_len);
+  size_t new_argz_len = *argz_len + count * suffix_len;
+  if (new_argz_len == 0)
+    return 0;
+  char *new_argz = malloc (new_argz_len);
+
+  if (new_argz)
+    {
+      char *p = new_argz, *entry;
+
+      for (entry = *argz;
+	   entry != NULL;
+	   entry = argz_next (*argz, *argz_len, entry))
+	{
+	  p = stpcpy (p, entry);
+	  p = stpcpy (p, suffix);
+	  p++;
+	}
+
+      free (*argz);
+      *argz = new_argz;
+      *argz_len = new_argz_len;
+
+      return 0;
+    }
+  else
+    return ENOMEM;
+}
+weak_alias (__argz_suffix_entries, argz_suffix_entries)
diff --git a/string/argz.h b/string/argz.h
index cbc588a8..bc6e484c 100644
--- a/string/argz.h
+++ b/string/argz.h
@@ -108,6 +108,16 @@ extern error_t argz_replace (char **__restrict __argz,
 			     const char *__restrict __str,
 			     const char *__restrict __with,
 			     unsigned int *__restrict __replace_count);
+
+/* Suffix each entry of ARGZ & ARGZ_LEN with SUFFIX.  Return 0 on success,
+   and ENOMEN if memory cannot be allocated.  */
+extern error_t __argz_suffix_entries (char **__restrict __argz,
+				      size_t *__restrict __argz_len,
+				      const char *__restrict __suffix);
+extern error_t argz_suffix_entries (char **__restrict __argz,
+				    size_t *__restrict __argz_len,
+				    const char *__restrict __suffix);
+
 \f
 /* Returns the next entry in ARGZ & ARGZ_LEN after ENTRY, or NULL if there
    are no more.  If entry is NULL, then the first entry is returned.  This