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

runtime/bin/directory_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 "bin/directory.h"
 
 #include <dirent.h>
 #include <errno.h>
 #include <string.h>
 #include <sys/param.h>
@@ skipping 10 matching lines @@
   }
 
   ~PathBuffer() {
     delete[] data;
   }
 
   char* data;
   int length;
 
   bool Add(const char* name) {
-    size_t written = snprintf(data + length,
-                              PATH_MAX - length,
-                              "%s",
-                              name);
+    int written = snprintf(data + length,
+                           PATH_MAX - length,
+                           "%s",
+                           name);
     data[PATH_MAX] = '\0';
-    if (written == strlen(name)) {
+    if (written <= PATH_MAX - length &&
+        written >= 0 &&
+        static_cast<size_t>(written) == strlen(name)) {
       length += written;
       return true;
     } else {
       errno = ENAMETOOLONG;
       return false;
     }
   }
 
   void Reset(int new_length) {
     length = new_length;
@@ skipping 329 matching lines @@
     return DeleteRecursively(&path);
   }
 }
 
 
 bool Directory::Rename(const char* path, const char* new_path) {
   ExistsResult exists = Exists(path);
   if (exists != EXISTS) return false;
   return (TEMP_FAILURE_RETRY(rename(path, new_path)) == 0);
 }