Function's argument type inference is affected by the functions return type when in a comprehension

Bug Report

MyPy seems to be getting confused if function that receives a generic class returns a union type with that generic is used in a comprehension. If the functions is used in a for loop or the function returns just the generic T, then MyPy doesn't show any errors.

To Reproduce

import dataclasses
from typing import Callable, TypeVar, Generic

T = TypeVar('T')


@dataclasses.dataclass(frozen=True, slots=True)
class Capsule(Generic[T]):
    builder: Callable[[], T]


def process(argument: Capsule[T]) -> T | RuntimeError:
    if isinstance((value := argument.builder()), int) and value % 2 != 0:
        return RuntimeError('Not an even number')

    return argument.builder()


encapsulated_ints = tuple(Capsule(builder=lambda: item) for item in range(10))

requests: list[int | RuntimeError] = []
for encapsulated_int in encapsulated_ints:
    request = process(encapsulated_int)
    requests.append(request)
requests = list(process(encapsulated_int) for encapsulated_int in encapsulated_ints)

Error:

main.py:25: error: Argument 1 to "process" has incompatible type "Capsule[int]"; expected "Capsule[int | RuntimeError]"  [arg-type]

https://mypy-play.net/?mypy=latest&python=3.12&gist=ffe7822cc564a6f347c2b8d6fd98c47f

Expected Behavior

The list comprehension line should be interpreted exactly the same as the for loop.

Actual Behavior

MyPy somehow relates the function return to the generic type.

Your Environment

• Mypy version used: 1.9.0
• Mypy command-line flags: no flags
• Mypy configuration options from mypy.ini (and other config files): no configs
• Python version used: 3.12

Inizia con il riproduttore Python nell’issue e confronta la diagnostica del ciclo for con quella della comprensione generatrice. Traccia come l’inferenza degli argomenti generici utilizza il tipo restituito dalla funzione in ciascun caso. Il lavoro è completato quando la comprensione viene accettata come il ciclo e un test di regressione copre l’esempio segnalato.