Different error code when assigning the result of a function to an annotated field

Bug Report

playground: https://mypy-play.net/?mypy=latest&python=3.12&gist=8c0d1a3a8e3f444fc12af3f803e18c59

from typing import Callable, TypeVar

_T = TypeVar("_T")

def Field(default_factory: Callable[[], _T]) -> _T: ...  # type: ignore[empty]


def new_list() -> list[int]:
    return []

class Model:
    a: list[str] = Field(default_factory=new_list)
    b: int = Field(default_factory=new_list)

The error for a is:

Argument "default_factory" to "Field" has incompatible type "Callable[[], list[int]]"; expected "Callable[[], list[str]]" [arg-type]

While the error for b is:

Incompatible types in assignment (expression has type "list[int]", variable has type "int") [assignment]

The error for b seems to be more correct/less confusing. Am I missing anything?

• Mypy version used: 1.12.0
• Mypy command-line flags: N/A
• Mypy configuration options from mypy.ini (and other config files): N/A
• Python version used: 3.12

Start with the linked mypy-play reproduction and compare the diagnostics produced for fields a and b. Trace how the annotated assignments and the Field call are analyzed, then check existing diagnostic tests for argument-type and assignment errors. Done means the behavior is clarified and the reported error is consistent with the intended type-checking rule.