Decide what should we do with doctests in CI

[sobolevn]

Bug report

Initial PR and discussion: #111682

So, here's the problem:

Example 1::

>>> 1 + 2
3

Example 2:

.. doctest::

>>> 1 + 2
3

We have two tools: doctest (builtin module) and sphinx (3rd party) that can run these samples as doctests. The problem is that they define "doctest" term differently:

• doctest module says that both of these examples are doctests
• sphinx says that only example with .. doctest:: directive is a doctest

This is problematic, because not all example are actually executed in CI, right now we have a CI job that uses Sphinx. So, in the result of this we have broken doctest (1st meaning) examples in the docs.

Examples:

• gh-54434: Make difflib.rst doctests pass. #111677
• gh-111181: Fix enum doctests #111180
• gh-111282: Fix NamedTemporaryFile example code #111283

What can we do?

Options:

1. Add .. doctest:: directives everywhere, but I think it is too much work and people will forget to do this
2. Try to use doctest_test_doctest_blocks, see docs https://www.sphinx-doc.org/en/master/usage/extensions/doctest.html This is what I plan to do locally and I will send a PR with the results. I fear that quite a lot of doctests might be broken
3. Add doctests to test_* files using something like

def load_tests(loader, tests, pattern):
    tests.addTests(doctest.DocFileSuite(
        os.path.join(REPO_ROOT, 'Doc/library/LIBNAME.rst'),
        module_relative=False,
    ))
    return tests

The last option is also problematic, because right now we can only run doctests in CI, when PR only touches Doc/ folder, I am not sure that it will be easy with this setup.

CC @AlexWaygood @AA-Turner

Linked PRs

• gh-111704: Add doctest_test_doctest_blocks option to Sphinx #111723

[sobolevn]

I hope that I will send the first PR today / tomorrow, but I am a bit sick :(

[AlexWaygood]

Option (2) is definitely attractive. Just two concerns from me:

1. How long will this make the Doctest CI job? It already takes 10 minutes to run all CPython's doctests via Sphinx; I worry that this option could make it significantly slower, by dramatically increasing the number of doctests run in CI. This is hypothetical, though; I might be wrong!
2. I agree with you that there'll probably be quite a few that fail at first. If we could figure out a way to tackle the errors incrementally, like what we've been doing with the Sphinx nitpicks, that would be ideal. Would it be possible to apply doctest_test_doctest_blocks only to certain files? (Cc. @AA-Turner again as the Sphinx expert here!)

[AlexWaygood]

Also, rest up and get well soon!

[hugovk]

Option 4: Modify Sphinx to run both types?

But I'm also concerned about the doctest taking longer. Of the three docs jobs, doctest is the longest at 10 minutes (= 3m setup/building + 7m doctest) compared to 2.5 minutes each for the other two:

Can we do them in parallel instead of sequential? Can the doctest module run them quicker?

[sobolevn]

Modify Sphinx to run both types?

This is option 2 :)

[sobolevn]

After working with make doctest for a while, here are my thoughts:

1. It does not allow to even run a single file (or maybe I cannot find the docs about it). This causes a lot of problems when debugging tests
2. It uses stuff that is fundamentally incompatible with -m doctest, like testsetup
3. It is hard to clean things up after usage (see gh-111726: Explicitly close database connections in sqlite3 doctests #111730), because you have to separate cleanup from the test itself (to not show it to user):

.. testcleanup::

   import os
   os.remove("tutorial.db")

4. If you want to skip some file, you have to:

• Change conf.py and add a test logic there
• Add :skipIf: TO ALL DOCTESTS in a file (see Doc/library/turtle.rst doctests are failing when tkinter is not present #111735)

I didn't like this tool at all.
It might be useful for small projects, but not for big ones.