Add asserts to kqueue filter/events on mac.

runtime/bin/eventhandler_macos.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "platform/globals.h"
 #if defined(TARGET_OS_MACOS)
 
 #include "bin/eventhandler.h"
 
 #include <errno.h>  // NOLINT
@@ skipping 255 matching lines @@
     // connections ready to be accepted.
     if (event->filter == EVFILT_READ) {
       if ((event->flags & EV_EOF) != 0) {
         if (event->fflags != 0) {
           event_mask |= (1 << kErrorEvent);
         } else {
           event_mask |= (1 << kCloseEvent);
         }
       }
       if (event_mask == 0) event_mask |= (1 << kInEvent);
+    } else {
+      UNREACHABLE();
     }
   } else {
     // Prioritize data events over close and error events.
     if (event->filter == EVFILT_READ) {
       if (FDUtils::AvailableBytes(sd->fd()) != 0) {
          event_mask = (1 << kInEvent);
       } else if ((event->flags & EV_EOF) != 0) {
         if (event->fflags != 0) {
           event_mask |= (1 << kErrorEvent);
         } else {
           event_mask |= (1 << kCloseEvent);
         }
         sd->MarkClosedRead();
       }
-    }
-
-    if (event->filter == EVFILT_WRITE) {
+    } else if (event->filter == EVFILT_WRITE) {
       if ((event->flags & EV_EOF) != 0) {
         if (event->fflags != 0) {
           event_mask |= (1 << kErrorEvent);
         } else {
           event_mask |= (1 << kCloseEvent);
         }
         // If the receiver closed for reading, close for writing,
         // update the registration with kqueue, and do not report a
         // write event.
         sd->MarkClosedWrite();
         UpdateKqueue(kqueue_fd_, sd);
       } else {
         event_mask |= (1 << kOutEvent);
       }
+    } else {
+      UNREACHABLE();
     }
   }
 
   return event_mask;
 }
 
 
 void EventHandlerImplementation::HandleEvents(struct kevent* events,
                                               int size) {
   for (int i = 0; i < size; i++) {
@@ skipping 100 matching lines @@
   return reinterpret_cast<void*>(fd + 1);
 }
 
 
 uint32_t EventHandlerImplementation::GetHashmapHashFromFd(intptr_t fd) {
   // The hashmap does not support keys with value 0.
   return dart::Utils::WordHash(fd + 1);
 }
 
 #endif  // defined(TARGET_OS_MACOS)