Document dataclass field should not be reused

Documentation

The current implementation of dataclass modifies a field in place. Thereby, the following code will modify f:

from dataclasses import dataclass, field

f = field(kw_only=True)

@dataclass
class A:
    x: int = f
    y: int = f

print(f) # now f.name is filled
# furthermore, A is broken (or does not behave if we used two different field instance)

It can create issues when we have multiple fields that have the same spec and we reuse the same Field instance to set the same metadata to all of them. A class is created but it's garbage.

IMHO, in the docs, we should warn the user to NOT share any Field instance.

Linked PRs

• gh-145373
• gh-145387

首先查阅 dataclass 和 Field 文档以及链接的 PR gh-145373 和 gh-145387。添加明确警告，不要在 dataclass 字段之间重复使用同一个 Field 实例；当文档中的指导处理了由此产生的变异和异常的类行为时，将 issue 中的示例视为完整。