Is there a canonical way to point back to the github issue from the test code, so that if the test passes at some point, it is easy to also close the issue?

Is there a canonical way to point back to the github issue from the test code, so that if the test passes at some point, it is easy to also close the issue?

I don't know about a canonical way, but any comment that points to the issue number / URL would probably be fine.
There's some existing test cases that do this in various ways.

Is there a canonical way to point back to the github issue from the test code, so that if the test passes at some point, it is easy to also close the issue?

I don't know about a canonical way, but any comment that points to the issue number / URL would probably be fine. There's some existing test cases that do this in various ways.

I added the URL as a comment.

I think this test would be better suited for check-expressions.test. There's a block of similar cases with the prefix testNoneReturn.

check-errorcodes.test is for tests related to error codes themselves.

This issue appear to affect any decorated function, so there may be value in including a test using an arbitrary dummy decorator, and with multiple levels of decoration.

For your consideration, please feel free to adapt as you see fit:

# test-data/unit/check-expressions.test
[case testNoneReturnDecorated]
from typing import Any, Callable, TypeVar

F = TypeVar('F', bound=Callable[..., Any])

def deco(f: F) -> F:
    pass

@deco
@deco
def f() -> None: 
    pass

class A:
    @staticmethod
    def s() -> None:
        pass

if int():
    x = f()      # E: "f" does not return a value (it only ever returns None)
if int():
    x = A.s()    # E: "s" of "A" does not return a value (it only ever returns None)
if int():
    x = A().s()  # E: "s" of "A" does not return a value (it only ever returns None)
[builtins fixtures/staticmethod.pyi]

I think this test would be better suited for check-expressions.test. There's a block of similar cases with the prefix testNoneReturn.

check-errorcodes.test is for tests related to error codes themselves.

Moved and renamed the test.

This issue appear to affect any decorated function, so there may be value in including a test using an arbitrary dummy decorator, and with multiple levels of decoration.

Good catch! I expanded the test based on your example.

EDIT: Also added an xfailing test for the __call__ method.