--- a/ChangeLog	Sat Feb 02 14:39:59 2019 -0800
+++ b/ChangeLog	Sun Feb 03 21:44:16 2019 +0100
@@ -1,3 +1,10 @@
+2019-02-03  Bruno Haible  <bruno@clisp.org>
+
+	Add script for determining the set of symbols to export from a library.
+	* build-aux/declared.sh: New file, from GNU libunistring.
+	* doc/lib-symbol-visibility.texi (Exported Symbols of Shared Libraries):
+	Mention it.
+
 2019-02-02  Paul Eggert  <eggert@cs.ucla.edu>
 
 	vla: add commentary about VLA_ELEMS

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/build-aux/declared.sh	Sun Feb 03 21:44:16 2019 +0100
@@ -0,0 +1,137 @@
+#! /bin/sh
+#
+# Copyright (C) 2006-2019 Free Software Foundation, Inc.
+#
+# This program 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.
+#
+# This program 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 this program.  If not, see <https://www.gnu.org/licenses/>.
+#
+
+# This script determines the declared global symbols in a C header file.
+# Assumptions:
+# - The header files are in C, with only C89 comments.
+# - No use of macros with parameters.
+# - All global declarations are marked with 'extern'.
+# - All declarations end in ';' on the same line.
+# - Not more than one symbol is declared in a declaration.
+
+# This script requires GNU sed.
+
+# func_usage
+# outputs to stdout the --help usage message.
+func_usage ()
+{
+  echo "\
+Usage: declared.sh [OPTION]... < SOURCE.h
+
+Extracts the declared global symbols of a C header file.
+
+Options:
+      --help           print this help and exit
+      --version        print version information and exit
+
+Report bugs to <bruno@clisp.org>."
+}
+
+# func_version
+# outputs to stdout the --version message.
+func_version ()
+{
+  echo "declared.sh (GNU libunistring)"
+  echo "Copyright (C) 2006-2018 Free Software Foundation, Inc.
+License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>
+This is free software: you are free to change and redistribute it.
+There is NO WARRANTY, to the extent permitted by law."
+  echo "Written by" "Bruno Haible"
+}
+
+# func_fatal_error message
+# outputs to stderr a fatal error message, and terminates the program.
+func_fatal_error ()
+{
+  echo "declared.sh: *** $1" 1>&2
+  echo "declared.sh: *** Stop." 1>&2
+  exit 1
+}
+
+# Command-line option processing.
+while test $# -gt 0; do
+  case "$1" in
+    --help | --hel | --he | --h )
+      func_usage
+      exit 0 ;;
+   --version | --versio | --versi | --vers | --ver | --ve | --v )
+      func_version
+      exit 0 ;;
+    -- )      # Stop option prcessing
+      shift; break ;;
+    -* )
+      func_fatal_error "unrecognized option: $option"
+      ;;
+    * )
+      break ;;
+  esac
+done
+
+if test $# -gt 0; then
+  func_fatal_error "too many arguments"
+fi
+
+# A sed expression that removes ANSI C and ISO C99 comments.
+sed_remove_comments="
+/[/][/*]/{
+  ta
+  :a
+  s,^\\(\\([^\"'/]\\|\"\\([^\\\"]\\|[\\].\\)*\"\\|'\\([^\\']\\|[\\].\\)*'\\|[/][^\"'/*]\\|[/]\"\\([^\\\"]\\|[\\].\\)*\"\\|[/]'\\([^\\']\\|[\\].\\)*'\\)*\\)//.*,\\1,
+  te
+  s,^\\(\\([^\"'/]\\|\"\\([^\\\"]\\|[\\].\\)*\"\\|'\\([^\\']\\|[\\].\\)*'\\|[/][^\"'/*]\\|[/]\"\\([^\\\"]\\|[\\].\\)*\"\\|[/]'\\([^\\']\\|[\\].\\)*'\\)*\\)/[*]\\([^*]\\|[*][^/*]\\)*[*][*]*/,\\1 ,
+  ta
+  /^\\([^\"'/]\\|\"\\([^\\\"]\\|[\\].\\)*\"\\|'\\([^\\']\\|[\\].\\)*'\\|[/][^\"'/*]\\|[/]\"\\([^\\\"]\\|[\\].\\)*\"\\|[/]'\\([^\\']\\|[\\].\\)*'\\)*[/][*]/{
+    s,^\\(\\([^\"'/]\\|\"\\([^\\\"]\\|[\\].\\)*\"\\|'\\([^\\']\\|[\\].\\)*'\\|[/][^\"'/*]\\|[/]\"\\([^\\\"]\\|[\\].\\)*\"\\|[/]'\\([^\\']\\|[\\].\\)*'\\)*\\)/[*].*,\\1 ,
+    tu
+    :u
+    n
+    s,^\\([^*]\\|[*][^/*]\\)*[*][*]*/,,
+    tv
+    s,^.*\$,,
+    bu
+    :v
+  }
+  :e
+}"
+
+# Check that 'sed' supports the kind of regular expressions used in
+# sed_remove_comments. The use of \| meaning alternation of basic regular
+# expressions is a GNU extension.
+sed_test='s,^\(\(a\|X\)*\)//.*,\1,'
+sed_result=`echo 'aaa//bcd' | sed -e "$sed_test"`
+test "$sed_result" = 'aaa' \
+  || func_fatal_error "The 'sed' program is not GNU sed. Try installing GNU sed."
+
+# A sed expression that joins 'extern' declarations that are broken over
+# several lines.
+sed_join_multiline_externs='
+/^extern [^;]*$/{
+  :a
+  N
+  s/\n/ /g
+  /^extern [^;]*$/{
+    ba
+  }
+}'
+
+# A sed expression that extracts the identifier of each 'extern' declaration.
+sed_extract_extern_declared='s/^extern [^()]* \([A-Za-z_][A-Za-z0-9_]*\) *[;(].*$/\1/p'
+
+sed -e "$sed_remove_comments" \
+  | sed -e "$sed_join_multiline_externs" \
+  | sed -n -e "$sed_extract_extern_declared"

--- a/doc/lib-symbol-visibility.texi	Sat Feb 02 14:39:59 2019 -0800
+++ b/doc/lib-symbol-visibility.texi	Sun Feb 03 21:44:16 2019 +0100
@@ -85,6 +85,8 @@
 @end itemize
 
 GNU libtool's @option{-export-symbols} option implements the first approach.
+The script @code{declared.sh} from Gnulib can help to produce the list of
+symbols.
 
 This gnulib module implements the third approach.  For this it relies on
 GNU GCC 4.0 or newer, namely on its @samp{-fvisibility=hidden} command-line