pytest: Assertions on nested comprehensions can give NameError

This test:

def test_nested_comprehension():
    s = [[True, True], [True, True]]
    assert all(e for row in s for e in row)

works fine in pytest 4.4.1 and 4.5.0. In pytest 4.6.1 it produces a NameError:

$ pytest
===================================================== test session starts =====================================================
platform darwin -- Python 3.7.3, pytest-4.6.1, py-1.8.0, pluggy-0.12.0
collected 1 item                                                                                                              

test_it.py F                                                                                                            [100%]

========================================================== FAILURES ===========================================================
__________________________________________________ test_nested_comprehension __________________________________________________

    def test_nested_comprehension():
        s = [[True, True], [True, True]]
>       assert all(e for row in s for e in row)
E       NameError: name 'e' is not defined

test_it.py:3: NameError
================================================== 1 failed in 0.06 seconds ===================================================

Pip list gives:

$ pip list
Package            Version
------------------ -------
atomicwrites       1.3.0  
attrs              19.1.0 
importlib-metadata 0.17   
more-itertools     7.0.0  
packaging          19.0   
pip                19.1.1 
pluggy             0.12.0 
py                 1.8.0  
pyparsing          2.4.0  
pytest             4.6.1  
setuptools         41.0.1 
six                1.12.0 
wcwidth            0.1.7  
wheel              0.33.4 
zipp               0.5.1