Cannot use --never-returning-functions for some functions

[timgkeller]

Version

pylint==2.7.2

Dependency

pytest

Steps to reproduce

Create a python file debug.py:

import pytest

def apparently_inconsistent_returning_function(return_something: bool) -> None:
    """A function that looks like not all paths return something."""
    if return_something:
        return None
    pytest.exit("Raises an exception.")

# pylint debug.py

=> R1710: Either all return statements in a function should return an expression, or none of them should. (inconsistent-return-statements)

This message is raised as pylint does not understand that pytest.exit raises an exception. Using --never-returning-functions="pytest.exit" should fix this behavior, however it doesn't:

# pylint debug.py --never-returning-functions="pytest.exit"

=> R1710: Either all return statements in a function should return an expression, or none of them should. (inconsistent-return-statements)

Expected behavior

pylint debug.py --never-returning-functions="pytest.exit" should not return an error for the above code.

Actual behavior

pylint debug.py --never-returning-functions="pytest.exit" still gives the error "inconsistent-return-statements"

Initial analysis

https://github.com/PyCQA/pylint/blob/master/pylint/checkers/refactoring/refactoring_checker.py#L1362

node.func is Attribute.exit(attrname='exit', expr=<Name.pytest l.7 at 0x7fab9184d898>)
node.func.inferred()[0] is "Uninferable", as a result there is no value we can set for --never-returning-functions that would get rid of the error "inconsistent-return-statements".

Workaround

import pytest

def pytest_exit(*args, **kwargs):
    """Call pytest.exit."""
    pytest.exit(*args, **kwargs)

def apparently_inconsistent_returning_function(return_something: bool) -> None:
    """A function that looks like not all paths return something."""
    if return_something:
        return None
    pytest_exit("Raises an exception.")

By wrapping pytest.exit in another function pytest_exit, node.func.inferred()[0] is now:

FunctionDef.pytest_exit(name='pytest_exit',
                        doc='Call pytest.exit.',
                        decorators=None,
                        args=<Arguments l.3 at 0x7f895a6b90f0>,
                        returns=None,
                        body=[<Expr l.5 at 0x7f895a6b9780>])

=> node.func.inferred()[0].qname() is "debug.pytest_exit" which we can use to get rid of the error "inconsistent-return-statements":

pylint debug.py --never-returning-functions="debug.pytest_exit"

[michael-k]

See #4122

pytest.exit seems to be annotated with NoReturn: https://github.com/pytest-dev/pytest/blob/c9e9a599fe5231da90967b6f77c73e17c12740b7/src/_pytest/outcomes.py#L113

[timgkeller]

See #4122

pytest.exit seems to be annotated with NoReturn: https://github.com/pytest-dev/pytest/blob/c9e9a599fe5231da90967b6f77c73e17c12740b7/src/_pytest/outcomes.py#L113

I like the suggestion in #4122. This would certainly help in this case and many others. Maybe it would also allow to get rid of --never-returning-functions. However, as long as this option persists, I think it should work for functions that do not have the NoReturn type hint.

[cdce8p]

Support for typing.NoReturn was just added with #4304.

The issue here however seems to be related to astroid. pytest.exit("Raises an exception.") is inferred as Uninferable and thus can't be checked against --never-returning-functions.