dart:io Directory.list: Fix use of snprintf return value to work with both C99, Windows, and pre-C9…

runtime/bin/directory_win.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 "bin/directory.h"
 
 #include <errno.h>
 #include <sys/stat.h>
 
 #include "bin/log.h"
 
 class PathBuffer {
  public:
   PathBuffer() : length(0) {
     data = new wchar_t[MAX_PATH + 1];
   }
 
   ~PathBuffer() {
     delete[] data;
   }
 
   wchar_t* data;
   int length;
 
   bool Add(const wchar_t* name) {
-    size_t written = _snwprintf(data + length,
-                               MAX_PATH - length,
-                               L"%s",
-                               name);
+    int written = _snwprintf(data + length,
+                             MAX_PATH - length,
+                             L"%s",
+                             name);
     data[MAX_PATH] = L'\0';
-    if (written == wcsnlen(name, MAX_PATH + 1)) {
+    if (written <= MAX_PATH - length &&
+        written >= 0 &&
+        static_cast<size_t>(written) == wcsnlen(name, MAX_PATH + 1)) {
       length += written;
       return true;
     } else {
       SetLastError(ERROR_BUFFER_OVERFLOW);
       return false;
     }
   }
 
   void Reset(int new_length) {
     length = new_length;
@@ skipping 345 matching lines @@
     bool success = Delete(new_path, true);
     if (!success) return false;
   }
   DWORD flags = MOVEFILE_WRITE_THROUGH;
   int move_status =
       MoveFileExW(system_path, system_new_path, flags);
   free(const_cast<wchar_t*>(system_path));
   free(const_cast<wchar_t*>(system_new_path));
   return (move_status != 0);
 }