dataclass tries to generate `__init__()` even though the class already defines one

Bug report

Bug description:

When running this code:

from dataclasses import dataclass

@dataclass
class A:
    a: int = 1

@dataclass
class B(A):
    b: int
    def __init__(self, *args, **kwargs): ...

I got TypeError: non-default argument 'b' follows default argument

However, if I set init=False for the second dataclass, like this:

from dataclasses import dataclass

@dataclass
class A:
    a: int = 1

@dataclass(init=False)
class B(A):
    b: int
    def __init__(self, *args, **kwargs): ...

There error disappeared.

I think the error comes from the process where dataclass tries to generate the default __init__() and checks the fields. But, if I understand correctly, this should not happen when the class already defines its own __init__().

Although I'm not sure whether the behavior should be defined as a bug, I do find the results inconsistant with the docs, which says

If the class already defines __init__(), this parameter (init) is ignored.

so, intuitively, adding init=False shouldn't have changed the result.

CPython versions tested on:

3.12, 3.13, 3.14

Operating systems tested on:

Windows

Linked PRs

• gh-151184
• gh-153601

使用 dataclasses.dataclass 重現這兩個範例，然後檢查 gh-151184 和 gh-153601 中連結的工作，再決定行為或文件是否不一致。完成的標準是：已確定對現有 init 的預期處理方式，並有適當的回歸證據涵蓋。