+
+# gl_CHECK_NEXT_HEADERS(HEADER1 HEADER2 ...)
+# ------------------------------------------
+# For each arg foo.h, if #include_next works, define NEXT_FOO_H to be
+# '<foo.h>'; otherwise define it to be
+# '"///usr/include/foo.h"', or whatever other absolute file name is suitable.
+# Also, if #include_next works as first preprocessing directive in a file,
+# define NEXT_AS_FIRST_DIRECTIVE_FOO_H to be '<foo.h>'; otherwise define it to
+# be
+# '"///usr/include/foo.h"', or whatever other absolute file name is suitable.
+# That way, a header file with the following line:
+# #@INCLUDE_NEXT@ @NEXT_FOO_H@
+# or
+# #@INCLUDE_NEXT_AS_FIRST_DIRECTIVE@ @NEXT_AS_FIRST_DIRECTIVE_FOO_H@
+# behaves (after sed substitution) as if it contained
+# #include_next <foo.h>
+# even if the compiler does not support include_next.
+# The three "///" are to pacify Sun C 5.8, which otherwise would say
+# "warning: #include of /usr/include/... may be non-portable".
+# Use `""', not `<>', so that the /// cannot be confused with a C99 comment.
+# Note: This macro assumes that the header file is not empty after
+# preprocessing, i.e. it does not only define preprocessor macros but also
+# provides some type/enum definitions or function/variable declarations.
+AC_DEFUN([gl_CHECK_NEXT_HEADERS],
+[
+ AC_REQUIRE([gl_INCLUDE_NEXT])
+ AC_REQUIRE([AC_CANONICAL_HOST])
+ AC_CHECK_HEADERS_ONCE([$1])
+
+ m4_foreach_w([gl_HEADER_NAME], [$1],
+ [AS_VAR_PUSHDEF([gl_next_header],
+ [gl_cv_next_]m4_defn([gl_HEADER_NAME]))
+ if test $gl_cv_have_include_next = yes; then
+ AS_VAR_SET([gl_next_header], ['<'gl_HEADER_NAME'>'])
+ else
+ AC_CACHE_CHECK(
+ [absolute name of <]m4_defn([gl_HEADER_NAME])[>],
+ m4_defn([gl_next_header]),
+ [AS_VAR_PUSHDEF([gl_header_exists],
+ [ac_cv_header_]m4_defn([gl_HEADER_NAME]))
+ if test AS_VAR_GET(gl_header_exists) = yes; then
+ AC_LANG_CONFTEST(
+ [AC_LANG_SOURCE(
+ [[#include <]]m4_dquote(m4_defn([gl_HEADER_NAME]))[[>]]
+ )])
+ dnl AIX "xlc -E" and "cc -E" omit #line directives for header files
+ dnl that contain only a #include of other header files and no
+ dnl non-comment tokens of their own. This leads to a failure to
+ dnl detect the absolute name of <dirent.h>, <signal.h>, <poll.h>
+ dnl and others. The workaround is to force preservation of comments
+ dnl through option -C. This ensures all necessary #line directives
+ dnl are present. GCC supports option -C as well.
+ case "$host_os" in
+ aix*) gl_absname_cpp="$ac_cpp -C" ;;
+ *) gl_absname_cpp="$ac_cpp" ;;
+ esac
+ dnl eval is necessary to expand gl_absname_cpp.
+ dnl Ultrix and Pyramid sh refuse to redirect output of eval,
+ dnl so use subshell.
+ AS_VAR_SET([gl_next_header],
+ ['"'`(eval "$gl_absname_cpp conftest.$ac_ext") 2>&AS_MESSAGE_LOG_FD |
+ sed -n '\#/]m4_defn([gl_HEADER_NAME])[#{
+ s#.*"\(.*/]m4_defn([gl_HEADER_NAME])[\)".*#\1#
+ s#^/[^/]#//&#
+ p
+ q
+ }'`'"'])
+ else
+ AS_VAR_SET([gl_next_header], ['<'gl_HEADER_NAME'>'])
+ fi
+ AS_VAR_POPDEF([gl_header_exists])])
+ fi
+ AC_SUBST(
+ AS_TR_CPP([NEXT_]m4_defn([gl_HEADER_NAME])),
+ [AS_VAR_GET([gl_next_header])])
+ if test $gl_cv_have_include_next = yes || test $gl_cv_have_include_next = buggy; then
+ # INCLUDE_NEXT_AS_FIRST_DIRECTIVE='include_next'
+ gl_next_as_first_directive='<'gl_HEADER_NAME'>'
+ else
+ # INCLUDE_NEXT_AS_FIRST_DIRECTIVE='include'
+ gl_next_as_first_directive=AS_VAR_GET([gl_next_header])
+ fi
+ AC_SUBST(
+ AS_TR_CPP([NEXT_AS_FIRST_DIRECTIVE_]m4_defn([gl_HEADER_NAME])),
+ [$gl_next_as_first_directive])
+ AS_VAR_POPDEF([gl_next_header])])
+])
+
+# Autoconf 2.68 added warnings for our use of AC_COMPILE_IFELSE;
+# this fallback is safe for all earlier autoconf versions.
+m4_define_default([AC_LANG_DEFINES_PROVIDED])