inet_ntop, inet_pton: avoid conflict with native Windows functions

[Bruno Haible]

Another possible conflict between the Windows inet_ntop, inet_pton functions
and the gnulib ones is at the source code level: When a compilation unit
includes first <arpa/inet.h> and then <ws2tcpip.h> (with _WIN32_WINNT >= 
0x0600),
there would be conflicting declarations of the rpl_inet_ntop or rpl_inet_ntop
functions.

This patch fixes it.


2019-06-30  Bruno Haible  <address@hidden>

        inet_ntop, inet_pton: Avoid conflict with native Windows functions.
        * m4/sys_socket_h.m4 (gl_PREREQ_SYS_H_WS2TCPIP): New macro, extracted
        from gl_PREREQ_SYS_H_SOCKET.
        (gl_PREREQ_SYS_H_SOCKET): Invoke it.
        * m4/arpa_inet_h.m4 (gl_HEADER_ARPA_INET): Invoke
        gl_PREREQ_SYS_H_WS2TCPIP.
        * modules/arpa_inet (Files): Add m4/sys_socket_h.m4, m4/socklen.m4.
        (Makefile.am): Substitute HAVE_WS2TCPIP_H.
        * lib/arpa_inet.in.h: Include <ws2tcpip.h>.

diff --git a/lib/arpa_inet.in.h b/lib/arpa_inet.in.h
index 430c3d3..96793ad 100644
--- a/lib/arpa_inet.in.h
+++ b/lib/arpa_inet.in.h
@@ -49,6 +49,12 @@
 #ifndef _@GUARD_PREFIX@_ARPA_INET_H
 #define _@GUARD_PREFIX@_ARPA_INET_H
 
+/* Get all possible declarations of inet_ntop() and inet_pton().  */
+#if (@GNULIB_INET_NTOP@ || @GNULIB_INET_PTON@ || defined GNULIB_POSIXCHECK) \
+    && @HAVE_WS2TCPIP_H@
+# include <ws2tcpip.h>
+#endif
+
 /* The definitions of _GL_FUNCDECL_RPL etc. are copied here.  */
 
 /* The definition of _GL_ARG_NONNULL is copied here.  */
diff --git a/m4/arpa_inet_h.m4 b/m4/arpa_inet_h.m4
index 46c7d28..645011d 100644
--- a/m4/arpa_inet_h.m4
+++ b/m4/arpa_inet_h.m4
@@ -1,4 +1,4 @@
-# arpa_inet_h.m4 serial 13
+# arpa_inet_h.m4 serial 14
 dnl Copyright (C) 2006, 2008-2019 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -24,6 +24,8 @@ AC_DEFUN([gl_HEADER_ARPA_INET],
 
   AC_REQUIRE([gl_FEATURES_H])
 
+  gl_PREREQ_SYS_H_WS2TCPIP
+
   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([[
diff --git a/m4/sys_socket_h.m4 b/m4/sys_socket_h.m4
index 1ea7b0b..d0a9020 100644
--- a/m4/sys_socket_h.m4
+++ b/m4/sys_socket_h.m4
@@ -1,4 +1,4 @@
-# sys_socket_h.m4 serial 23
+# sys_socket_h.m4 serial 24
 dnl Copyright (C) 2005-2019 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -104,17 +104,11 @@ AC_DEFUN([gl_PREREQ_SYS_H_SOCKET],
   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
-    if test $ac_cv_header_ws2tcpip_h = yes; then
-      HAVE_WS2TCPIP_H=1
-    else
-      HAVE_WS2TCPIP_H=0
-    fi
   fi
   AC_SUBST([HAVE_SYS_SOCKET_H])
-  AC_SUBST([HAVE_WS2TCPIP_H])
+  gl_PREREQ_SYS_H_WS2TCPIP
 ])
 
 # Common prerequisites of the <sys/socket.h> replacement and of the
@@ -142,6 +136,24 @@ AC_DEFUN([gl_PREREQ_SYS_H_WINSOCK2],
   AC_SUBST([HAVE_WINSOCK2_H])
 ])
 
+# Common prerequisites of the <sys/socket.h> replacement and of the
+# <arpa/inet.h> replacement.
+# Sets and substitutes HAVE_WS2TCPIP_H.
+AC_DEFUN([gl_PREREQ_SYS_H_WS2TCPIP],
+[
+  AC_REQUIRE([gl_CHECK_SOCKET_HEADERS])
+  if test $ac_cv_header_sys_socket_h = yes; then
+    HAVE_WS2TCPIP_H=0
+  else
+    if test $ac_cv_header_ws2tcpip_h = yes; then
+      HAVE_WS2TCPIP_H=1
+    else
+      HAVE_WS2TCPIP_H=0
+    fi
+  fi
+  AC_SUBST([HAVE_WS2TCPIP_H])
+])
+
 AC_DEFUN([gl_SYS_SOCKET_MODULE_INDICATOR],
 [
   dnl Use AC_REQUIRE here, so that the default settings are expanded once only.
diff --git a/modules/arpa_inet b/modules/arpa_inet
index 005690f..317bf8d 100644
--- a/modules/arpa_inet
+++ b/modules/arpa_inet
@@ -4,6 +4,8 @@ A GNU-like <arpa/inet.h>.
 Files:
 lib/arpa_inet.in.h
 m4/arpa_inet_h.m4
+m4/sys_socket_h.m4
+m4/socklen.m4
 
 Depends-on:
 include_next
@@ -34,6 +36,7 @@ arpa/inet.h: arpa_inet.in.h $(top_builddir)/config.status 
$(CXXDEFS_H) $(WARN_ON
              -e 's|@''HAVE_ARPA_INET_H''@|$(HAVE_ARPA_INET_H)|g' \
              -e 's/@''GNULIB_INET_NTOP''@/$(GNULIB_INET_NTOP)/g' \
              -e 's/@''GNULIB_INET_PTON''@/$(GNULIB_INET_PTON)/g' \
+             -e 's|@''HAVE_WS2TCPIP_H''@|$(HAVE_WS2TCPIP_H)|g' \
              -e 's|@''HAVE_DECL_INET_NTOP''@|$(HAVE_DECL_INET_NTOP)|g' \
              -e 's|@''HAVE_DECL_INET_PTON''@|$(HAVE_DECL_INET_PTON)|g' \
              -e 's|@''REPLACE_INET_NTOP''@|$(REPLACE_INET_NTOP)|g' \