Mypy fails to infer type parameters when composing generic functions with themselves

Bug Report

Mypy incorrectly infers Never types when the same generic function is used in multiple argument positions of a higher-order generic function, preventing proper composition of identical generic functions.

To Reproduce

from collections.abc import Callable

def compose[A, B, C](first: Callable[[A], B], second: Callable[[B], C]) -> Callable[[A], C]: ...

def id[T](value: T) -> list[T]: ...  # any generic would do

compose(id, id)
# Argument 1 to "compose" has incompatible type "Callable[[T], list[T]]"; expected "Callable[[Never], Never]"
# Argument 2 to "compose" has incompatible type "Callable[[T], list[T]]"; expected "Callable[[Never], Never]"

Expected Behavior

1. The first id function should be inferred as Callable[[T], list[T]]
2. The second id function should be inferred as Callable[[list[T]], list[list[T]]]
3. The resulting composition should be Callable[[T], list[list[T]]]

Actual Behavior

Mypy fails to infer type parameters.

Your Environment

• Mypy version used: 1.15.0
• Mypy command-line flags: --strict
• Mypy configuration options from mypy.ini (and other config files): none
• Python version used: 3.13

Inizia riproducendo l’esempio compose(id, id) con mypy 1.15.0, Python 3.13 e --strict. Traccia l’inferenza dei tipi generici per le due posizioni degli argomenti callable; il lavoro è completato quando il tipo callable annidato previsto viene inferito senza errori Never e un test di regressione copre il caso.