gh-149879: Fix test_socket on Cygwin (#149913)

Disable SCM_RIGHTS, recvmsg(), sendmsg() and sethostname() on Cygwin.

Author: vstinner

Lib/test/test_socket.py

@@ -1454,7 +1454,7 @@ def testIPv6toString(self):
         assertInvalid('1:2:3:4:5:6:')
         assertInvalid('1:2:3:4:5:6:7:8:0')
         # bpo-29972: inet_pton() doesn't fail on AIX
-        if not AIX:
+        if not AIX and sys.platform != 'cygwin':
             assertInvalid('1:2:3:4:5:6:7:8:')
 
         self.assertEqual(b'\x00' * 12 + b'\xfe\x2a\x17\x40',
@@ -2001,7 +2001,8 @@ def test_getfqdn_filter_localhost(self):
         self.assertEqual(socket.getfqdn(), socket.getfqdn("::"))
 
     @unittest.skipUnless(socket_helper.IPV6_ENABLED, 'IPv6 required for this test.')
-    @unittest.skipIf(sys.platform == 'win32', 'does not work on Windows')
+    @unittest.skipIf(sys.platform in ('win32', 'cygwin'),
+                     'does not work on Windows')
     @unittest.skipIf(AIX, 'Symbolic scope id does not work')
     @unittest.skipUnless(hasattr(socket, 'if_nameindex'), "test needs socket.if_nameindex()")
     @support.skip_android_selinux('if_nameindex')
@@ -2035,7 +2036,7 @@ def test_getaddrinfo_ipv6_scopeid_numeric(self):
         self.assertEqual(sockaddr, ('ff02::1de:c0:face:8d', 1234, 0, ifindex))
 
     @unittest.skipUnless(socket_helper.IPV6_ENABLED, 'IPv6 required for this test.')
-    @unittest.skipIf(sys.platform == 'win32', 'does not work on Windows')
+    @unittest.skipIf(sys.platform in ('win32', 'cygwin'), 'does not work on Windows')
     @unittest.skipIf(AIX, 'Symbolic scope id does not work')
     @unittest.skipUnless(hasattr(socket, 'if_nameindex'), "test needs socket.if_nameindex()")
     @support.skip_android_selinux('if_nameindex')

Modules/socketmodule.c

@@ -654,10 +654,6 @@ class _socket.socket "PySocketSockObject *" "clinic_state()->sock_type"
 [clinic start generated code]*/
 /*[clinic end generated code: output=da39a3ee5e6b4b0d input=2db2489bd2219fd8]*/
 
-#define clinic_state() (find_module_state_by_def(type))
-#include "clinic/socketmodule.c.h"
-#undef clinic_state
-
 /* XXX There's a problem here: *static* functions are not supposed to have
    a Py prefix (or use CapitalizedWords).  Later... */
 
@@ -688,6 +684,18 @@ class _socket.socket "PySocketSockObject *" "clinic_state()->sock_type"
 #define IS_SELECTABLE(s) (_PyIsSelectable_fd((s)->sock_fd) || (s)->sock_timeout <= 0)
 #endif
 
+// SCM_RIGHTS, sendmsg(), recvmsg() and sethostname() don't work properly on
+// Cygwin: disable these features.
+#ifdef __CYGWIN__
+#  undef CMSG_LEN
+#  undef SCM_RIGHTS
+#  undef HAVE_SETHOSTNAME
+#endif
+
+#define clinic_state() (find_module_state_by_def(type))
+#include "clinic/socketmodule.c.h"
+#undef clinic_state
+
 static PyObject*
 select_error(void)
 {