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

Empieza revisando la documentación de dataclass y Field y los PR enlazados gh-145373 y gh-145387. Añade una advertencia clara de no reutilizar una instancia de Field entre campos de dataclass, y considera completo el ejemplo de la issue cuando la orientación documentada aborde la mutación resultante y el comportamiento defectuoso de la clase.