@mlouielu, thanks for your PR! By analyzing the history of the files in this pull request, we identified @terryjreedy to be a potential reviewer.

The test that failed on the two Windows bots after the update merge is this:
FAIL: test_open_completions (idlelib.idle_test.test_autocomplete.AutoCompleteTest)

Traceback (most recent call last):
File "C:\projects\cpython\lib\idlelib\idle_test\test_autocomplete.py", line 157, in test_open_completions
self.assertTrue(self.autocomplete.open_completions(False, True, True))
AssertionError: None is not true

It sometimes failed for me when run by test.regrtest, but never did when running directly under unittest.

The tests for _open_completions_later and _delayed_open_completion do not be duplicated for attributes and files as the mode has no impact on those functions. I used the second test instead for better coverage.

I documented within open_completions the three possible calls and the arguments passed by each. We only need to test those 3 combinations and not the 5 others never used. The modes are only used for the delayed calls after . in code or / in strings. The False, True, True pattern in the failure is the one for a tab withing a string.

I did a new update merge, fixed the merge conflict, and python -m test -ugui test_idle failed 3 successive times. Commenting out the one line (now 160), the same passed 5 times. I will push now with that line disabled to run CI while I investigate. (Pushed with line enabled, disabled in web editor after failure on Azure.)

Thanks @mlouielu for the PR, and @terryjreedy for merging it 🌮🎉.. I'm working now to backport this PR to: 3.7.
🐍🍒⛏🤖

GH-12529 is a backport of this pull request to the 3.7 branch.