Add config for enabling rst

[jayvdb]

It would be helpful to have an easy way to include *.rst by default, without (ab)using addopts.

https://pypi.org/project/pytest-doctestplus/ provides this.

[Erotemic]

This is a reasonable request.

Do you mainly want to use it via the pytest runner, or would you want the native runner to support this as well?

[jayvdb]

My only interest is usage via pytest.

[Erotemic]

Looking into this I found that you can use --xdoctest-glob *.rst, but this causes the document to be parsed as a text file and as such only lines prefixed with >>> are parsed. I assume this isn't what you want to happen.

I think it would be good to define the desired behavior a bit more precisely, because right now I'm unsure.

Are we only looking to support blocks of code that look like this:

.. code-block:: python

    >>> import foo
    >>> foo.bar()

or would we want to run all code snippets? How should we deal with something like this?

.. code:: python


    def func1():
        """
        Example:
            >>> assert func1() == 1
        """
        return 1

[jayvdb]

that is no different to

>>> def func1():
>>>     """
>>>     Example:
>>>         >>> assert func1() == 1
>>>     """
>>>     return 1

doctest ignores nested doctest.
See PyCQA/pyflakes@6734c37 and PyCQA/pyflakes@93aa3c4 for some more unusual scenarios and indicating what doctest does/doesnt process.