shutil: Inconsistent return types when using pathlib

Bug report

Bug description:

Using pathlib with shutil usually works, but there are some quirks when it comes to return types. As an example, see the copy function (but other functions are affected as well):

https://github.com/python/cpython/blob/67ded6a4faae29edff8e4f7886978e71ce116e33/Lib/shutil.py#L468-L484

In this case, if a Path object gets passed in as dst, it will be returned unchanged if it is not a directory, but a str will be returned if it is a directory. That's unexpected, the return type should be consistent, probably by always returning a str.

I assume that pathlib support is mostly incidental in shutil, considering that the latter predates the former. shutil should probably be reviewed for proper pathlib support at some point. (See also a few other pathlib/shutil related issues reported here.)

CPython versions tested on:

CPython main branch

Operating systems tested on:

No response

Linked PRs

• gh-132820

先检查链接的 PR gh-132820，然后检查 Lib/shutil.py 中 copy 附近的代码，以及报告中提到的其他 pathlib 相关函数。查看现有的 shutil 测试，并确保受影响的函数具有一致且有文档说明的返回类型，同时使用测试覆盖作为目录和不作为目录的 Path 目标。