attr-defined error is raised when reading default value of an InitVar field of a dataclass

Bug Report
I wrote a code that reads the default value of an InitVar field of a dataclass and got attr-defined error from mypy==1.18.2. But cpython==3.13.3,3.12.10 does run without error and I believe it is reasonable to assume one can read default values from InitVar fields reading the reference.

To Reproduce

import dataclasses


@dataclasses.dataclass
class Foo:
    foo: int = 42
    bar: dataclasses.InitVar[int] = 42


print(Foo.foo)
print(Foo.bar)

Expected Behavior

no-error

Actual Behavior

<string>:12: error: "type[Foo]" has no attribute "bar"  [attr-defined]

Your Environment

Mypy version used: 1.18.2, 1.17.1
Mypy command-line flags: none
Mypy configuration options from mypy.ini (and other config files): none
Python version used: 3.13.3, 3.12.10

Hello, there is a test that explicitly enforces the current behavior. Is this issue still a bug or it works as intended? The test is added around 4 years ago so I wonder if anything changes since.

[case testDataclassInitVarCannotBeSet]
from dataclasses import dataclass, InitVar

@dataclass
class C:
    x: InitVar[int] = 0
    y: InitVar[str] = ''

    def f(self) -> None:
        # This works at runtime, but it seems like an abuse of the InitVar
        # feature and thus we don't support it
        self.x = 1  # E: "C" has no attribute "x"
        self.y: str = 'x'  # E: "C" has no attribute "y"

c = C()
c2 = C(x=1)
c.x  # E: "C" has no attribute "x"

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attr-defined error is raised when reading default value of an `InitVar` field of a dataclass #19889

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attr-defined error is raised when reading default value of an InitVar field of a dataclass #19889

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tqa236 commented on Nov 8, 2026

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attr-defined error is raised when reading default value of an `InitVar` field of a dataclass #19889