Reland: Make File.create() fail when a directory exists at the same path

runtime/bin/file_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/file.h"
 
 #include <copyfile.h>  // NOLINT
@@ skipping 212 matching lines @@
 
 
 File* File::OpenStdio(int fd) {
   return ((fd < 0) || (2 < fd)) ? NULL : new File(new FileHandle(fd));
 }
 
 
 bool File::Exists(const char* name) {
   struct stat st;
   if (NO_RETRY_EXPECTED(stat(name, &st)) == 0) {
-    return S_ISREG(st.st_mode);
+    // Everything but a directory and a link is a file to Dart.
+    return !S_ISDIR(st.st_mode) && !S_ISLNK(st.st_mode);
   } else {
     return false;
   }
 }
 
 
 bool File::Create(const char* name) {
   int fd = TEMP_FAILURE_RETRY(open(name, O_RDONLY | O_CREAT, 0666));
   if (fd < 0) {
     return false;
   }
-  return (close(fd) == 0);
+  // File.create returns a File, so we shouldn't be giving the illusion that the
+  // call has created a file or that a file already exists if there is already
+  // an entity at the same path that is a directory or a link.
+  bool is_file = true;
+  struct stat st;
+  if (NO_RETRY_EXPECTED(fstat(fd, &st)) == 0) {
+    if (S_ISDIR(st.st_mode)) {
+      errno = EISDIR;
+      is_file = false;
+    } else if (S_ISLNK(st.st_mode)) {
+      errno = ENOENT;
+      is_file = false;
+    }
+  }
+  FDUtils::SaveErrorAndClose(fd);
+  return is_file;
 }
 
 
 bool File::CreateLink(const char* name, const char* target) {
   int status = NO_RETRY_EXPECTED(symlink(target, name));
   return (status == 0);
 }
 
 
 bool File::Delete(const char* name) {
@@ skipping 227 matching lines @@
   return ((file_1_info.st_ino == file_2_info.st_ino) &&
           (file_1_info.st_dev == file_2_info.st_dev))
              ? File::kIdentical
              : File::kDifferent;
 }
 
 }  // namespace bin
 }  // namespace dart
 
 #endif  // defined(TARGET_OS_MACOS)