gnu: glibc: Look for locale data in versioned sub-directories.

Suggested by Mark H Weaver <mhw@netris.org>.

* gnu/packages/patches/glibc-versioned-locpath.patch: New file.
* gnu-system.am (dist_patch_DATA): Add it.
* gnu/packages/base.scm (glibc)[source]: Use it.
  [arguments]: Add explicit version sub-directory to
  libc_cv_localedir.
  [native-search-paths]: Use 'GUIX_LOCPATH' instead of 'LOCPATH'.
  (glibc-locales, glibc-utf8-locales): Write to a VERSION
  sub-directory.

doc/guix.texi

@@ -933,24 +933,24 @@ daemons on the same machine.
 @node Application Setup
 @section Application Setup
 
-When using Guix on top of GNU/Linux distribution other than GuixSD, a
+When using Guix on top of GNU/Linux distribution other than GuixSD---a
-few additional steps are needed to get everything in place.  Here are
+so-called @dfn{foreign distro}---a few additional steps are needed to
-some of them.
+get everything in place.  Here are some of them.
 
 @subsection Locales
 
 @anchor{locales-and-locpath}
 @cindex locales, when not on GuixSD
 @vindex LOCPATH
+@vindex GUIX_LOCPATH
 Packages installed @i{via} Guix will not use the host system's locale
 data.  Instead, you must first install one of the locale packages
-available with Guix and then define the @code{LOCPATH} environment
+available with Guix and then define the @code{GUIX_LOCPATH} environment
-variable (@pxref{Locale Names, @code{LOCPATH},, libc, The GNU C Library
+variable:
-Reference Manual}):
 
 @example
 $ guix package -i glibc-locales
-$ export LOCPATH=$HOME/.guix-profile/lib/locale
+$ export GUIX_LOCPATH=$HOME/.guix-profile/lib/locale
 @end example
 
 Note that the @code{glibc-locales} package contains data for all the
@@ -958,6 +958,28 @@ locales supported by the GNU@tie{}libc and weighs in at around
 110@tie{}MiB.  Alternately, the @code{glibc-utf8-locales} is smaller but
 limited to a few UTF-8 locales.
 
+The @code{GUIX_LOCPATH} variable plays a role similar to @code{LOCPATH}
+(@pxref{Locale Names, @code{LOCPATH},, libc, The GNU C Library Reference
+Manual}).  There are two important differences though:
+
+@enumerate
+@item
+@code{GUIX_LOCPATH} is honored only by Guix's libc, and not by the libc
+provided by foreign distros.  Thus, using @code{GUIX_LOCPATH} allows you
+to make sure the the foreign distro's programs will not end up loading
+incompatible locale data.
+
+@item
+libc suffixes each entry of @code{GUIX_LOCPATH} with @code{/X.Y}, where
+@code{X.Y} is the libc version---e.g., @code{2.22}.  This means that,
+should your Guix profile contain a mixture of programs linked against
+different libc version, each libc version will only try to load locale
+data in the right format.
+@end enumerate
+
+This is important because the locale data format used by different libc
+versions may be incompatible.
+
 @subsection X11 Fonts
 
 The majority of graphical applications use Fontconfig to locate and

gnu-system.am

@@ -472,6 +472,7 @@ dist_patch_DATA =						\
   gnu/packages/patches/glibc-locales.patch			\
   gnu/packages/patches/glibc-locale-incompatibility.patch	\
   gnu/packages/patches/glibc-o-largefile.patch			\
+  gnu/packages/patches/glibc-versioned-locpath.patch		\
   gnu/packages/patches/gmp-arm-asm-nothumb.patch		\
   gnu/packages/patches/gnucash-price-quotes-perl.patch		\
   gnu/packages/patches/gnutls-doc-fix.patch			\

gnu/packages/base.scm

@@ -484,6 +484,7 @@ store.")
             (patches (map search-patch
                           '("glibc-ldd-x86_64.patch"
                             "glibc-locale-incompatibility.patch"
+                            "glibc-versioned-locpath.patch"
                             "glibc-o-largefile.patch")))))
    (build-system gnu-build-system)
 
@@ -614,7 +615,9 @@ store.")
 
    (native-search-paths
     ;; Search path for packages that provide locale data.  This is useful
-    ;; primarily in build environments.
+    ;; primarily in build environments.  Use 'GUIX_LOCPATH' rather than
+    ;; 'LOCPATH' to avoid interference with the host system's libc on foreign
+    ;; distros.
     (list (search-path-specification
            (variable "GUIX_LOCPATH")
            (files '("lib/locale")))))
@@ -657,7 +660,7 @@ the 'share/locale' sub-directory of this package.")
             (alist-delete 'install ,phases)))
          ((#:configure-flags flags)
           `(append ,flags
-                   ;; Use $(libdir)/locale as is the case by default.
+                   ;; Use $(libdir)/locale/X.Y as is the case by default.
                    (list (string-append "libc_cv_localedir="
                                         (assoc-ref %outputs "out")
                                         "/lib/locale/"

gnu/packages/patches/glibc-versioned-locpath.patch

@@ -0,0 +1,240 @@
+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.
+
+--- a/locale/newlocale.c
++++ b/locale/newlocale.c
+@@ -30,6 +30,7 @@
+ /* 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							      \
+@@ -48,7 +49,6 @@ __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;
+ 
+@@ -102,17 +102,8 @@ __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 ead030d..0c0e314 100644
+--- a/locale/setlocale.c
++++ b/locale/setlocale.c
+@@ -215,12 +215,65 @@ setdata (int category, struct __locale_data *data)
+     }
+ }
+ 
++/* Return in *LOCALE_PATH and *LOCALE_PATH_LEN the locale data search path as
++   a colon-separated 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_create_sep (guix_locpath_var, ':',
++			     locale_path, locale_path_len) != 0
++	  || __argz_suffix_entries (locale_path, locale_path_len,
++				    "/" VERSION) != 0)
++	goto bail_out;
++    }
++
++  if (locpath_var != NULL && locpath_var[0] != '\0')
++    {
++      char *reg_locale_path = NULL;
++      size_t reg_locale_path_len = 0;
++
++      if (__argz_create_sep (locpath_var, ':',
++			     &reg_locale_path, &reg_locale_path_len) != 0)
++	goto bail_out;
++
++      if (__argz_append (locale_path, locale_path_len,
++			 reg_locale_path, reg_locale_path_len) != 0)
++	goto bail_out;
++
++      free (reg_locale_path);
++    }
++
++  if (*locale_path != NULL)
++    {
++      /* Append the system default locale directory.  */
++      if (__argz_add_sep (locale_path, locale_path_len,
++			  _nl_default_locale_path, ':') != 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.  */
+@@ -251,17 +304,10 @@ 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 8424a61..f925503 100644
+--- a/string/Makefile
++++ b/string/Makefile
+@@ -38,7 +38,7 @@ routines	:= strcat strchr strcmp strcoll strcpy strcspn		\
+ 		   swab strfry memfrob memmem rawmemchr strchrnul	\
+ 		   $(addprefix argz-,append count create ctsep next	\
+ 				     delete extract insert stringify	\
+-				     addsep replace)			\
++				     addsep replace suffix)		\
+ 		   envz basename					\
+ 		   strcoll_l strxfrm_l string-inlines memrchr		\
+ 		   xpg-strerror strerror_l
+diff --git a/string/argz-suffix.c b/string/argz-suffix.c
+new file mode 100644
+index 0000000..505b0f2
+--- /dev/null
++++ b/string/argz-suffix.c
+@@ -0,0 +1,56 @@
++/* 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;
++  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 bb62a31..d276a35 100644
+--- a/string/argz.h
++++ b/string/argz.h
+@@ -134,6 +134,16 @@ 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);
++
+ 
+ /* 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