--doctest-modules ignores module-attribute docstrings

[edit: mistakenly submitted without description]

Description

Module-level attributes with docstrings underneath (or sphinx-comments prefixed with #:) are ignored when doctesting modules.

• Standard python's doctest module also ignores module-data docstrings
  (so we can claim this "not a bug"), yet ...
• Sphinx consider these as valid docstrings, and
• Sphinx's doctest builder also validates them.

Example

Running pytest --doctest-modules on the module below named foo.py:

def f():
    """
    This doctest works:

    >>> 1 + 1
    1
    """

a = 1
"""
But this doctest is ignored:

>>> 1 + 1
4
"""

#: Also this doctest is ignored:
#:
#: >>> 1 + 1
#: 3
b = 1


if __name__ == "__main__":
    import doctest
    doctest.testmod()

• raises just 1 error (1 + 1 = 4),
• python foo.py also raises 1 error, but ...
• if you setup a small site, include this module with auto-documenter, and launch python setup.py build_sphinx -b doctest (or make html), the doctest sphinx-builder takes both docstring of a and b module data members into account, and screams 3 times!

Versions

$ pip list|grep pytest
pytest                             5.3.5       
pytest-cov                         2.8.1       
pytest-sphinx                      0.2.2       
pytest-sugar                       0.9.2      

Start with the foo.py example and reproduce the behavior using pytest --doctest-modules, comparing it with doctest.testmod() and the Sphinx doctest builder described in the issue. The work is done when doctests in both ordinary module-attribute docstrings and #: documentation comments are discovered and validated by pytest.