gh-129573: Fix possible abort from non-string suggestions in calculate_suggestions/_Py_CalculateSuggestions

[devdanzin]

This PR adds a simple check that suggestion candidates are strings in calculate_suggestions(3.12)/_Py_CalculateSuggestions(main), avoiding an abort in debug builds from code like below:

importrunpyrunpy._run_module_code("blech",{0: "", "bluch": ""}, "")

The abort only happens in 3.12, because the code in main checks for non-string candidates in _suggestions__generate_suggestions_impl. However, since the affected code is still present in main, this PR is against that branch.

In main, the code above exits the new REPL, which will be reported as a new issue with associated PR.

Found using fusil by @vstinner.

• Issue: Failed assertion in _PyUnicode_Equal from calculate_suggestions with non-string candidate #129573

[vstinner]

test_traceback is failing on the CI.

[python-cla-bot]

All commit authors signed the Contributor License Agreement.

[vstinner]

@devdanzin: Tests are failing on your PR, and you didn't sign the CLA. What's the status of this PR?

[devdanzin]

I'm sorry, I've left this one fall behind. Would you like to take it over?

I have signed the CLA and even contributed some trivial code, I'll wait to see if it's a CLA bot issue or my CLA status changed to unverified somehow.

[vstinner]

Suggested change

	runpy._run_module_code("blech",{0: "", "bluch": ""}, "")
	# non-string global variable
	runpy._run_module_code("blech",{0: "", "bluch": ""}, "")

[vstinner]

_suggestions._generate_suggestions() checks if all elements are strings before calling _Py_CalculateSuggestions(). So this test doesn't check changed code.