Incorrect "Attributes without a default cannot follow attributes with one" in dataclasses

[reinhrst]

Mypy incorrectly (in my understanding) complains about members in dataclasses having default values, even though many dataclasses.field assignments do not actually assign a default value.

I feel the correct behaviour should be to only detect an error if a field assignment that leads to a default value being assigned in the init method is followed by a default value.

This results (incorrectly) in an error:

import dataclasses

@dataclasses.dataclass
class A:
    x: int = dataclasses.field(metadata={"doc": "foo"})
    y: str

So does this:

import dataclasses

@dataclasses.dataclass
class A:
    x: int = dataclasses.field(init=False, default=1)
    y: str

Whereas this does not emit an error (where it should):

import dataclasses

@dataclasses.dataclass
class A:
    x: int = dataclasses.field(default=1)
    y: str = dataclasses.field(metadata={"doc": "foo"})

I understand that there may be quite some complexities to fix this correctly, but I would suggest in that case just removing this check altogether until it works correctly.

Tested on python 3.7.2 with mypy 0.670 and master, and python 3.6.6 with mypy 0.670

[ilevkivskyi]

Sorry for late answer, these examples indeed look like a bug. I think the fix can be simple, just use RefExpr in _collect_field_args.

[ilevkivskyi]

Here is the fix #6739