Incomplete and incorrect stub generation of a dataclass.

[nknavasto]

Bug Report
Stubs for a dataclass are incomplete and depending on the use case also incorrect. Consider the following dataclass:

# module.py
import dataclasses


@dataclasses.dataclass
class A:
    foo: str
    bar: str = "default"
    baz: str = dataclasses.field(default="hidden default", init=False)

    def method(self, a: int) -> float:
        return 0.0

The resulting generated stubs are

import dataclasses

@dataclasses.dataclass
class A:
    foo: str
    bar: str = ...
    baz: str = ...
    def method(self, a: int) -> float: ...
    def __init__(self, foo, bar) -> None: ...

As you can see, the method method received the correct type hints. However, the __init__ method did not. It correctly removed the baz parameter, as this has the init=False flag, but no type hints are present. Also, it does not reflect the fact, that bar is only an optional parameter. This leads to incorrect type hints when using this dataclass.

To Reproduce
Run stubgen module.py.

Expected Behavior

The expected behavior could look something like this:

import dataclasses

@dataclasses.dataclass
class A:
    foo: str
    bar: str = ...
    baz: str = ...
    def method(self, a: int) -> float: ...
    def __init__(self, foo: str, bar: str = "default") -> None: ...

Your Environment

• Mypy version used: 1.8.0
• Mypy command-line flags: none
• Mypy configuration options from mypy.ini (and other config files): none
• Python version used: 3.8