gh-128911: Add tests on the PyImport C API

[vstinner]

• Add Modules/_testlimitedcapi/import.c
• Add Lib/test/test_capi/test_import.py
• Remove _testcapi.check_pyimport_addmodule(): tests already covered by newly added tests.

• Issue: [C API] Add PyImport_GetModuleAttrString(mod_name, attr_name) helper function #128911

[vstinner]

cc @serhiy-storchaka @encukou

[vstinner]

Importing asyncio package works if test_capi.test_import is run alone, but fails with the following error when test_capi is run:

ERROR: test_importmodule (test.test_capi.test_import.ImportTests.test_importmodule) (name='asyncio')
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/runner/work/cpython/cpython-ro-srcdir/Lib/test/test_capi/test_import.py", line 42, in check_import_fresh_module
    module = import_module(name)
  File "/home/runner/work/cpython/cpython-ro-srcdir/Lib/asyncio/__init__.py", line 25, in <module>
    __all__ = (base_events.__all__ +
               ^^^^^^^^^^^
NameError: name 'base_events' is not defined

For now, I modified the tests to not import asyncio.

[vstinner]

I will merge my PR as it is when the CI passed, to be able to add tests in my following #128912 PR.

I didn't add tests for non-UTF8 strings, nor NULL tests for PyImport_ImportModuleLevel(). For PyImport_ImportModuleLevel(), it's tricky because some arguments are ignored for level=0 and I don't know how to write tests for level > 0.

@serhiy-storchaka: Maybe you would be interested to work on follow-up PR to increase the test coverage / test more cases?

[serhiy-storchaka]

Do you allow me to commit directly in your branch? It is better to have a single clean commit in the logs than several commits that rewrite one other.

[vstinner]

@serhiy-storchaka: Ok, you can push changes to my branch.

[serhiy-storchaka]

I pushed my changes. Please review them.

It seems that I found bugs in the current code:

1. PyImport_ExecCodeModuleObject() leaves a non-string name in sys.module after raising AttributeError.
2. There is a difference in __spec__.origin between PyImport_ExecCodeModuleWithPathnames() and PyImport_ExecCodeModuleObject() if the first pathname is NULL and the second pathname is not NULL.

[vstinner]

I pushed my changes. Please review them.

I pushed a cleanup changes. With this cleanup, the change (additional tests) LGTM.

It seems that I found bugs in the current code

Oh, interesting.

[vstinner]

@serhiy-storchaka: Thanks for additional tests and reviews.

I enabled auto-merge.

[miss-islington-app]

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

[miss-islington-app]

Thanks @vstinner for the PR 🌮🎉.. I'm working now to backport this PR to: 3.12.
🐍🍒⛏🤖 I'm not a witch! I'm not a witch!

[miss-islington-app]

Sorry, @vstinner, I could not cleanly backport this to 3.13 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker d95ba9fa1110534b7247fa2ff12b90e930c93256 3.13

[miss-islington-app]

Sorry, @vstinner, I could not cleanly backport this to 3.12 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker d95ba9fa1110534b7247fa2ff12b90e930c93256 3.12