Relative links to directories don't work on Windows

[sgrekhov]

Link.create() documentation says nothing special about relative links on Windows. So, seems, that they should work. But they don't. For example, the tests below works well on Linux but fails on Windows

import "dart:io";

main() async {
  Directory sandbox = Directory.systemTemp.createTempSync();
  try {
    Directory target =
      new Directory(sandbox.path + Platform.pathSeparator + "dir1");
    target.createSync();
    Link link = new Link(sandbox.path + Platform.pathSeparator + "link.lnk");
    await link.create("dir1").then((Link created) {
      print(created.targetSync()); // Linux: dir1, Windows: dir1
      print(FileSystemEntity.typeSync(created.path)); // Linux: directory, Windows: link
      print(created.resolveSymbolicLinksSync()); // Linux: /tmp/PRVKQP/dir1, Windows: FileSystemException: Cannot resolve symbolic links, path = 'C:\Users\sgrek\AppData\Local\Temp\aba06b27\link.lnk' (OS Error: Access denied , errno = 5)
    });
  } finally {
    sandbox.deleteSync(recursive: true);
  }
}

On Windows, Link pointing to a not existing entity has type link (see #53684 (comment)). So, exception is, probably, also caused by the fact that relative link on Windows cannot find its target. Anyway, please fix it or document that relative links on Windows not supported or have some limitations

Probably this is the same issue as #45981

Tested on Dart SDK version: 3.2.0-228.0.dev (dev) (Tue Oct 3 21:02:12 2023 -0700) on "windows_x64"

[sgrekhov]

Issue exists for directories only (changed title accordingly). Test below works well on both Windows and Linux

import "dart:io";

main() async {
  Directory sandbox = Directory.systemTemp.createTempSync();
  try {
    File target =
      new File(sandbox.path + Platform.pathSeparator + "file.txt");
    target.createSync();
    Link link = new Link(sandbox.path + Platform.pathSeparator + "link.lnk");
    await link.create("file.txt").then((Link created) {
      print(created.targetSync()); // Linux: file.txt, Windows: file.txt
      print(FileSystemEntity.typeSync(created.path)); // Linux: file, Windows: file
      print(created.resolveSymbolicLinksSync()); // Linux: /tmp/XNQSRN/file.txt, Windows: C:\Users\sgrek\AppData\Local\Temp\fd9d7667\file.txt
      // Now create a directory and move the link to it. Its relative path
      // should point to a not existing entity after it
      Directory dir = sandbox.createTempSync();
      Link moved =
        created.renameSync(dir.path + Platform.pathSeparator + "moved.lnk");
      print(moved.targetSync()); // Linux: file.txt, Windows: file.txt
      print(FileSystemEntity.typeSync(moved.path));  // Linux: notFound, Windows: link
    });
  } finally {
    sandbox.deleteSync(recursive: true);
  }
}

[brianquinlan]

I can't reproduce this. The output using Dart 3.4.0 is:

dir1
directory
C:\Users\brian\AppData\Local\Temp\d89223bb\dir1

Possibly this was fixed in 097c84f ?

If these tests are disabled in co19, could you try to reenable them and see if they still fail?

[sgrekhov]

Yes, the issue was fixed in 097c84f and appropriate co19 tests were updated accordingly.
See dart-lang/co19@d04448a and dart-lang/co19@3011a2e. So, I believe, this issue can be closed.