Final class variable in dataclass breaks __init__ signature

[ncanceill]

Describe the bug
Python 3.13 allows ClassVar[Final[<type>]] annotations for dataclass fields. Pyright 1.1.390 accepts the annotation but gets the __init__() signature wrong.

When a dataclass field is annotated as ClassVar[Final[<type>]] it is not added as parameter to the generated __init__() method. The dataclass below has a final class variable bar with a default value followed by an instance variable baz without default value. Python 3.13 accepts this code and generates a method __init__(self, baz) as expected.

Pyright 1.1.390 seems to parse bar as a regular field and therefore:

• does not accept baz because it comes after a field with a default value
• computes a wrong signature __init__(self, bar = 0, baz)

Code or Screenshots

from dataclasses import dataclass
from typing import ClassVar, Final, reveal_type

@dataclass
class Foo:
    bar: ClassVar[Final[int]] = 0
    baz: int
    # Fields without default values cannot appear after fields with default values (reportGeneralTypeIssues)

Foo(1)
# Argument missing for parameter "baz" (reportCallIssue)

reveal_type(Foo.__init__)
# Type of "Foo.__init__" is "(self: Foo, bar: int = 0, baz: int) -> None"

Additional info

This passes Pyright but forgoes the Final annotation:

@dataclass
class Foo:
    bar: ClassVar[int] = 0
    baz: int

reveal_type(Foo.__init__)
# Type of "Foo.__init__" is "(self: Foo, baz: int) -> None"

This still gets the wrong signature:

@dataclass
class Foo:
    baz: int
    bar: ClassVar[Final[int]] = 0

reveal_type(Foo.__init__)
# Type of "Foo.__init__" is "(self: Foo, baz: int, bar: int = 0) -> None"

So does this:

@dataclass(kw_only=True)
class Foo:
    bar: ClassVar[Final[int]] = 0
    baz: int

reveal_type(Foo.__init__)
# Type of "Foo.__init__" is "(self: Foo, *, bar: int = 0, baz: int) -> None"

As noted in #8676 (comment) the Python 3.13.0 implementation does not treat dataclass fields annotated Final[ClassVar[<type>]] as class variables. As a result, Pyright is correct here:

@dataclass
class Foo:
    bar: Final[ClassVar[int]] = 0
    baz: int
    # Fields without default values cannot appear after fields with default values (reportGeneralTypeIssues)

Foo(1)
# Argument missing for parameter "baz" (reportCallIssue)

reveal_type(Foo.__init__)
# Type of "Foo.__init__" is "(self: Foo, bar: int = 0, baz: int) -> None"

VS Code extension or command-line
Command-line, Python 3.13.0, Pyright 1.1.390

[erictraut]

Thanks for reporting the issue. I agree it's a bug.

[erictraut]

This is addressed in pyright 1.1.391.