[PATCHv4] gethostname: fix build on mingw

[Eric Blake]

Since commit 4e86671a, gethostname failed to compile on mingw.
Gnulib's sys/socket.h includes winsock2.h, which then includes
unistd.h prior to declaring gethostname.  The fix is to ensure
that our replacement unistd.h does not declare any replacements
until we are sure that winsock2.h is completely included.

* lib/unistd.in.h (includes): Work around fact that mingw
<winsock2.h> re-includes <unistd.h>, by avoiding any
redeclarations if we are being included by <winsock2.h>.
Reported by Matthias Bolte.

Signed-off-by: Eric Blake <address@hidden>
---

Try 4.  This time, try localizing all the changes to just our
replacement <unistd.h>.  Detect whether we are being indirectly
included by <winsock2.h>, so that clients should not have to
adjust their calling patterns (although they DO need to explcitly
include <unistd.h> if they plan on using gethostname, rather
than relying on the nonstandard <winsock2.h> to provide it).

 ChangeLog       |    8 ++++++++
 lib/unistd.in.h |   28 +++++++++++++++++++++++++---
 2 files changed, 33 insertions(+), 3 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index cc3ef5a..22dfca0 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+2010-03-22  Eric Blake  <address@hidden>
+
+       gethostname: fix build on mingw
+       * lib/unistd.in.h (includes): Work around fact that mingw
+       <winsock2.h> re-includes <unistd.h>, by avoiding any
+       redeclarations if we are being included by <winsock2.h>.
+       Reported by Matthias Bolte.
+
 2010-03-20  Bruno Haible  <address@hidden>

        * m4/unlink.m4 (gl_FUNC_UNLINK): Fix last commit.
diff --git a/lib/unistd.in.h b/lib/unistd.in.h
index b74484a..b2b92c8 100644
--- a/lib/unistd.in.h
+++ b/lib/unistd.in.h
@@ -15,7 +15,23 @@
    along with this program; if not, write to the Free Software Foundation,
    Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */

-#ifndef _GL_UNISTD_H
+/* Special invocation convention:
+   - On mingw, several headers, including <winsock2.h>, include <unistd.h>,
+     but we need to ensure that both the system <unistd.h> and <winsock2.h>
+     are completely included before we replace gethostname.  */
+#if @UNISTD_H_HAVE_WINSOCK2_H@ && !defined _GL_WINSOCK2_H_WITNESS \
+  && defined _WINSOCK2_H
+/* <unistd.h> is being indirectly included for the first time from
+   <winsock2.h>; avoid declaring any overrides.  */
+# if @HAVE_UNISTD_H
+#  @INCLUDE_NEXT@ @NEXT_UNISTD_H@
+# else
+#  error unexpected; report this to address@hidden
+# endif
+# define _GL_WINSOCK2_H_WITNESS
+
+/* Normal invocation.  */
+#elif !defined _GL_UNISTD_H

 #if __GNUC__ >= 3
 @PRAGMA_SYSTEM_HEADER@
@@ -26,7 +42,14 @@
 # @INCLUDE_NEXT@ @NEXT_UNISTD_H@
 #endif

-#ifndef _GL_UNISTD_H
+/* Get all possible declarations of gethostname().  */
+#if @UNISTD_H_HAVE_WINSOCK2_H@ && !defined _GL_INCLUDING_WINSOCK2_H
+# define _GL_INCLUDING_WINSOCK2_H
+# include <winsock2.h>
+# undef _GL_INCLUDING_WINSOCK2_H
+#endif
+
+#if !defined _GL_UNISTD_H && !defined _GL_INCLUDING_WINSOCK2_H
 #define _GL_UNISTD_H

 /* NetBSD 5.0 mis-defines NULL.  Also get size_t.  */
@@ -76,7 +99,6 @@
 #if @GNULIB_GETHOSTNAME@
 /* Get all possible declarations of gethostname().  */
 # if @UNISTD_H_HAVE_WINSOCK2_H@
-#  include <winsock2.h>
 #  if !defined _GL_SYS_SOCKET_H
 #   undef socket
 #   define socket               socket_used_without_including_sys_socket_h
-- 
1.6.6.1