Literal typeguard

Feature

Infer str is an instance of Literal based on code path:

from typing import Literal


def f(x: Literal["a", "b"]):
    ...


def g(x: str):
    if x == "a":
        ...
    elif x == "b":
        ...
    else:
        raise ValueError()
    f(x) # ERROR: "f" has incompatible type "str"; expected "Union[Literal['a'], Literal['b']]"

Mypy reports error for the above code, but x is actually an instance of Literal["a", "b"], because all values other than "a" or "b" raises ValueError.
Pyright, one of type checkers, can infer this code has no problem.

Start with the Python reproducer in the issue and compare mypy's result with the stated Pyright behavior. No source files or tests are named, so locating the relevant type-narrowing implementation and existing test conventions is part of the work. Done means the call to f(x) is accepted after the exhaustive checks while other paths remain correctly handled.