read_dir 迭代的时候给到的是一个 io::Result<DirEntry>，文档里面只是简单说了 New errors may be encountered after an iterator is initially constructed.

但是具体这个 New errors 到底是什么？

我试过了在迭代的时候对文件夹或者里面的文件作删除、重命名、改变权限，都没有返回 error； （测试平台包括 Mac 和 Linux，没有 windows 暂时没测）。

/// Iterator over the entries in a directory.
///
/// This iterator is returned from the [`read_dir`] function of this module and
/// will yield instances of [`io::Result`]`<`[`DirEntry`]`>`. Through a [`DirEntry`]
/// information like the entry's path and possibly other metadata can be
/// learned.
///
/// The order in which this iterator returns entries is platform and filesystem
/// dependent.
///
/// # Errors
///
/// This [`io::Result`] will be an [`Err`] if there's some sort of intermittent
/// IO error during iteration.
#[stable(feature = "rust1", since = "1.0.0")]
#[derive(Debug)]
pub struct ReadDir(fs_imp::ReadDir);

This [io::Result] will be an [Err] if there's some sort of intermittent IO error during iteration.

看起来一定要是比较罕见的 IO 错误？