function call that returns Never incorrectly marked as unreachable when function that's defined later with multiple argument decorator is called

sorry for the wacky title

from typing import TypeVar, Literal
from typing_extensions import assert_never

Fn = TypeVar("Fn")


def foo(fn: Fn, value: bool = False) -> Fn:
    ...


def bar(value: Literal[True]) -> None:
    if value:
        baz()
    else:
        assert_never(value) # error: Statement is unreachable  [unreachable]


@foo
def baz() -> None:
    ...

playground

functions that return Never are not supposed to be marked as unreachable - see #10916 (comment)

Looks similar to #8900

minified:

from typing import _T as T

def foo() -> None:
    return bar()
    exit()  # error: Statement is unreachable  [unreachable]

def deco(fn: T, a: bool = False) -> T: ...

@deco
def bar() -> None: ...

also causes an invalid 'Expression has type "Any"' error:

from typing import TypeVar

Fn = TypeVar("Fn")

def foo(fn: Fn, value: bool = False) -> Fn:
    ...


def f() -> None:
    baz()
    try:
        ...
    except Exception as ex:  # error: Expression has type "Any"  [misc]
        pass

@foo
def baz() -> None:
    ...

playground

very related (probably the same issue?): #13167

Fix spurious unreachable and disallow-any errors from deferred passes

Fix spurious unreachable and disallow-any errors from deferred passes (…

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function call that returns `Never` incorrectly marked as unreachable when function that's defined later with multiple argument decorator is called #13043

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function call that returns Never incorrectly marked as unreachable when function that's defined later with multiple argument decorator is called #13043

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KotlinIsland commented on Jun 30, 2022

DetachHead commented on Aug 11, 2022

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function call that returns `Never` incorrectly marked as unreachable when function that's defined later with multiple argument decorator is called #13043