- if test -n "$SYS_SOCKET_H"; then
- dnl Check prerequisites of the <sys/socket.h> replacement.
- gl_CHECK_NEXT_HEADERS([sys/socket.h])
- if test $ac_cv_header_sys_socket_h = yes; then
- HAVE_SYS_SOCKET_H=1
- HAVE_WS2TCPIP_H=0
+ gl_PREREQ_SYS_H_WINSOCK2
+
+ dnl Check for declarations of anything we want to poison if the
+ dnl corresponding gnulib module is not in use.
+ gl_WARN_ON_USE_PREPARE([[
+/* Some systems require prerequisite headers. */
+#include <sys/types.h>
+#include <sys/socket.h>
+ ]], [socket connect accept bind getpeername getsockname getsockopt
+ listen recv send recvfrom sendto setsockopt shutdown accept4])
+])
+
+AC_DEFUN([gl_PREREQ_SYS_H_SOCKET],
+[
+ dnl Check prerequisites of the <sys/socket.h> replacement.
+ gl_CHECK_NEXT_HEADERS([sys/socket.h])
+ if test $ac_cv_header_sys_socket_h = yes; then
+ HAVE_SYS_SOCKET_H=1
+ HAVE_WS2TCPIP_H=0
+ else
+ HAVE_SYS_SOCKET_H=0
+ dnl We cannot use AC_CHECK_HEADERS_ONCE here, because that would make
+ dnl the check for those headers unconditional; yet cygwin reports
+ dnl that the headers are present but cannot be compiled (since on
+ dnl cygwin, all socket information should come from sys/socket.h).
+ AC_CHECK_HEADERS([ws2tcpip.h])
+ if test $ac_cv_header_ws2tcpip_h = yes; then
+ HAVE_WS2TCPIP_H=1