Raise an exception when "request" is used as a parametrization argument

[nikoskaragiannakis]

I just found, accidentally, that this

@pytest.mark.parametrize('request, expected', [(1, 1)])
def test_foo(request, expected):
    assert request == expected

would raise an error

...
    def get_direct_param_fixture_func(request):
>       return request.param
E       AttributeError: 'int' object has no attribute 'param'

Wouldn't it be helpful if there was a helpful exception raised here https://github.com/pytest-dev/pytest/blob/master/src/_pytest/fixtures.py#L881-L882?

For example, if

            if argname != "request":
                fixturedef.addfinalizer(functools.partial(self.finish, request=request))
            else:
                raise ValueError('`request` cannot be use as a parametrization name')

(or a better message) in the case of the initial example gives

self = <FixtureDef name='request' scope='function' baseid=''>
request = <SubRequest 'request' for <Function 'test_foo[1-1]'>>

    def execute(self, request):
        # get required arguments and register our own finish()
        # with their finalization
        for argname in self.argnames:
            fixturedef = request._get_active_fixturedef(argname)
            if argname != "request":
                fixturedef.addfinalizer(functools.partial(self.finish, request=request))
            else:
>               raise ValueError('`request` cannot be use as a parametrization name')
E               ValueError: `request` cannot be use as a parametrization name

The pytest version i'm using is 3.10.0

[nicoddemus]

Thanks @nikoskaragiannakis for the report!