Segfault when manipulating a recursive union #15192

Bug Report

Running mypy on the following program produces a segfault.

To Reproduce

from typing import Literal, TypeAlias, Union


Expr: TypeAlias = Union[
    tuple[Literal["const"], int],
    tuple[Literal["neg"], "Expr"],
]


def eval(e: Expr) -> int:
    if e[0] == "const":
        return e[1]
    elif e[0] == "neg":
        return -eval(e[1])

Expected Behavior

Mypy returns successfully.

Actual Behavior

Mypy segfaults:

fish: Job 1, 'mypy ...' terminated by signal SIGSEGV (Address boundary error)

The problem can be replicated in the mypy playground.

Your Environment

• Mypy version used: 1.2.0
• Mypy command-line flags: none
• Mypy configuration options from mypy.ini (and other config files): none
• Python version used: 3.11