Reland "[io] exclude links from isDirectory()"

This is a reland of 49d743f

Original change's description:
> [io] exclude links from isDirectory()
> 
> isDirectory() should not return true for links.
> 
> Bug: #35102
> Change-Id: I737345a581d6a50d7bccab0dbc10f1a31a57e219
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/121900
> Commit-Queue: Zichang Guo <zichangguo@google.com>
> Reviewed-by: Siva Annamalai <asiva@google.com>

Bug: #35102
Change-Id: Ifa4317ec77172d3f196f6f75307b940d614e27bb
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/122028
Reviewed-by: Siva Annamalai <asiva@google.com>
Commit-Queue: Zichang Guo <zichangguo@google.com>

Author: zichangg

sdk/lib/_internal/vm/bin/file_patch.dart

@@ -217,7 +217,9 @@ class _FileSystemWatcher {
         bool getIsDir(event) {
           if (Platform.isWindows) {
             // Windows does not get 'isDir' as part of the event.
-            return FileSystemEntity.isDirectorySync(getPath(event));
+            // Links should also be skipped.
+            return FileSystemEntity.isDirectorySync(getPath(event)) &&
+                !FileSystemEntity.isLinkSync(getPath(event));
           }
           return (event[0] & FileSystemEvent._isDir) != 0;
         }

sdk_nnbd/lib/_internal/vm/bin/file_patch.dart

@@ -219,7 +219,9 @@ class _FileSystemWatcher {
         bool getIsDir(event) {
           if (Platform.isWindows) {
             // Windows does not get 'isDir' as part of the event.
-            return FileSystemEntity.isDirectorySync(getPath(event));
+            // Links should also be skipped.
+            return FileSystemEntity.isDirectorySync(getPath(event)) &&
+                !FileSystemEntity.isLinkSync(getPath(event));
           }
           return (event[0] & FileSystemEvent._isDir) != 0;
         }

tests/standalone_2/io/link_test.dart

@@ -275,10 +275,36 @@ testRelativeLinksSync() {
   tempDirectory.deleteSync(recursive: true);
 }
 
+testIsDir() async {
+  if (!Platform.isWindows && !Platform.isLinux && !Platform.isMacOS) return;
+  Directory sandbox = Directory.systemTemp.createTempSync();
+  Directory dir = new Directory(sandbox.path + Platform.pathSeparator + "dir");
+  dir.createSync();
+  File target = new File(sandbox.path + Platform.pathSeparator + "target");
+  target.createSync();
+
+  final eventCompleter = new Completer<FileSystemEvent>();
+  var subscription;
+  subscription = dir.watch().listen((FileSystemEvent event) {
+    if (event.path.endsWith('link')) {
+      eventCompleter.complete(event);
+      subscription.cancel();
+    }
+  });
+  Link link = new Link(dir.path + Platform.pathSeparator + "link");
+  link.createSync(target.path);
+  final event = await eventCompleter.future;
+  // Link should not be marked as Dir.
+  Expect.isFalse(event.isDirectory);
+
+  sandbox.deleteSync(recursive: true);
+}
+
 main() {
   testCreateSync();
   testCreateLoopingLink();
   testRenameSync();
   testLinkErrorSync();
   testRelativeLinksSync();
+  testIsDir();
 }