False Positive W0621: Redefining name %r from outer scope when using pytest fixtures

[orSolocate]

Bug description

Bug opened from SO issue

Testcase:

# test_wallet.py

@pytest.fixture
def my_wallet():
    '''Returns a Wallet instance with a zero balance'''
    return Wallet()

@pytest.mark.parametrize("earned,spent,expected", [
    (30, 10, 20),
    (20, 2, 18),
])
def test_transactions(my_wallet, earned, spent, expected):
    my_wallet.add_cash(earned)
    my_wallet.spend_cash(spent)
    assert my_wallet.balance == expected

They discuss a workaround to avoid the error and also a method of disabling the checker but this bug issue is about actually fixing it in Pylint, or at least discussing it.

Configuration

No response

Pylint output

`W0621: Redefining name %r from outer scope (line %s)'`

Expected behavior

The Pylint message should recognize this situation of pytest fixture decorator and don't raise a message.

Pylint version

pylint 2.8.4
astroid 2.5.8
Python 3.7.5

OS / Environment

Windows

Additional dependencies

No response

[Pierre-Sassoulas]

Well, apparently this code crash on 2.14.0-dev0 and 2.13.8.

Exception on node <Decorators l.2 at 0x7f1be24aaa00> in file '/home/pierre/pylint/b.py'
Traceback (most recent call last):
  File "/home/pierre/pylint/pylint/utils/ast_walker.py", line 73, in walk
    callback(astroid)
  File "/home/pierre/pylint/pylint/checkers/unsupported_version.py", line 64, in visit_decorators
    self._check_typing_final(node)
  File "/home/pierre/pylint/pylint/checkers/unsupported_version.py", line 79, in _check_typing_final
    for decorator in decorators or uninferable_final_decorators(node):
  File "/home/pierre/pylint/pylint/checkers/utils.py", line 825, in uninferable_final_decorators
    import_node = decorator.expr.lookup(decorator.expr.name)[1][0]
IndexError: tuple index out of range

[DanielNoord]

We should probably fix the crash, but the issue of handling pytest fixtures should probably be delegated to pytest-pylint.

[mbyrnepr2]

We should probably fix the crash

I can take a look.

#6532

[mbyrnepr2]

I could be wrong but regarding the "Refined name from outer scope" message. Isn't this correct of Pylint in highlighting what is also mentioned in the SO (pytest docs)?

If a fixture is used in the same module in which it is defined, the function name of the fixture will be shadowed by the function arg that requests the fixture; one way to resolve this is to name the decorated function fixture and then use @pytest.fixture(name='').

[Pierre-Sassoulas]

Related : #1535

[lqueryvg]

How about my comment here:
https://stackoverflow.com/questions/46089480/pytest-fixtures-redefining-name-from-outer-scope-pylint/54045715?noredirect=1#comment122655133_57015304
I.e. you get a similar problem with mocker.
from pytest_mock import mocker followed by def test_my_thing(mocker) gives same lint error. Seems to be a recurring theme.

[DanielNoord]

These issues are probably best reported to https://github.com/reverbc/pylint-pytest/. Due to the way pytest creates its fixtures and mocks it's difficult for pylint to infer these as it does not follow the traditional/standard pattern of Pythonic code. Therefore, such issues are better handled by a pylint plugin that is focused on understanding those particular patterns.
Similarly, there is https://github.com/PyCQA/pylint-django which does the same but then for common Django patterns. There is simply not enough maintainers-bandwidth to support all these plugins within the main pylint project.