gh-116402: Avoid readline in test_builtin TTY input tests

[ambv]

The intention here is to make the TTY input() tests run in as many scenarios as possible. For this to happen, we need to temporarily remove the function pointer set to call_readline in PyInit_readline(). This pointer is normally NULL without readline and PyOS_Readline uses a basic implementation of its own in this case. This is what we want.

We could try and avoid importing readline in tests, but we have played this whack-a-mole for a long time. For instance, now that pdb uses rlcompleter, test_builtin imports that always (since it imports doctest in load_tests() and doctest imports pdb as it subclasses it). I think we should stop trying to not load readline, and just detach its function temporarily. This avoids discussions of "unimporting" readline, which would be problematic as PyInit_readline() sets global state on the C side through setup_readline.

While CI is famously not run with a TTY and those tests will be skipped there, people running tests sequentially from their terminal will now be able to have those tests run in many more situations than before.

I did the function pointer unsetting with ctypes for simplicity. If that's unavailable, the context manager simply skips the tests.

• Issue: [macOS] test_builtin.PtyTests.test_input_tty hangs if rlcompleter is imported #116402

[ambv]

@Eclips4, can you confirm this fixes the issue for you?

[Eclips4]

@Eclips4, can you confirm this fixes the issue for you?

Yes! Thanks for the fix!

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @ambv for commit fa61261 🤖

If you want to schedule another build, you need to add the 🔨 test-with-buildbots label again.

[JelleZijlstra]

Thanks, this also fixes test_builtin for me locally.

[ambv]

All buildbots (including refleaks and bigmem) passed save for "iOS ARM64 Simulator" with an unrelated failure. Rebasing on main with the try:finally: suggestion and landing as soon as CI passes.

[miss-islington-app]

Thanks @ambv for the PR 🌮🎉.. I'm working now to backport this PR to: 3.13.
🐍🍒⛏🤖

[bedevere-app]

GH-122472 is a backport of this pull request to the 3.13 branch.