it seems file_exists returns true for a symlink on windows when the target doesn't exist even though the documentation says otherwise. We'd need a more elaborate check.

Thats a windows specific issue as a broken symlink is still a "file" for windows.
You'd need to read that file and make sure, it actually exist like so:

if (is_link($path)) {
    $target = readlink($path);

    if ($target === false || !file_exists($target)) {
        echo "Broken symlink\n";
    }
}

Are you sure readlink returns false on windows?

Its not primarily about readlink returning false, but it returns the path the the actually symlinked file. So in your case !file_exists($target) would then be true.

$target === false is just a precaution to make sure a path is actually returned.

I plan to add a more complete check that the symlink points to the right target.

@markstory @LordSimal Did a more general check and logic.