Suppress unnecessary-list-index-lookup for whole loop on write

[timmartin]

Type of Changes

	Type
✓	🐛 Bug fix

Description

The unnecessary-list-index-lookup checker was assuming that if the
subscript was written to then it would only invalidate access on later
lines, but this is not necessarily the case if an inner loop is nested
inside the one being checked.

Closes #6818

[timmartin]

I was going to apply the same change to unnecessary-dict-index-lookup, but I discovered that we already have a regression test that would be regressed by this change:

for k, v in a_dict.items():
    print(a_dict[k])  # [unnecessary-dict-index-lookup]
    print(b_dict[k])  # Should not emit warning, accessing other dictionary
    a_dict[k] = 123  # Should not emit warning, key access necessary
    a_dict[k] += 123  # Should not emit warning, key access necessary
    print(a_dict[k])  # Should not emit warning, v != a_dict[k]****

We could just update the regression test, but I was going to have a go at changing the behavior to detect whether there is a loop of any kind nested within the outer for loop. I think if there is no inner loop we can stick with the old behavior and only suppress the warnings if there is a nested loop. This seems reasonable, but I'm worried that it will make the code hard to follow.

[coveralls]

Pull Request Test Coverage Report for Build 2478175748

• 17 of 19 (89.47%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.007%) to 95.519%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pylint/checkers/refactoring/refactoring_checker.py	17	19	89.47%

Totals
Change from base Build 2478058828:	-0.007%
Covered Lines:	16371
Relevant Lines:	17139

---

💛 - Coveralls

[timmartin]

I'm not sure I understand the build errors here. It seems to be a problem reported from a Javascript process, so it's not obvious how my changes could have affected it.

[Pierre-Sassoulas]

I think it's due to other fails before:

************* Module pylint.checkers.refactoring.refactoring_checker
pylint/checkers/refactoring/refactoring_checker.py:2136:0: C0401: Wrong spelling of a word 'fo' in a comment:
# end fo the loop without updating the collection
      ^^
Did you mean: ''few' or 'of''? (wrong-spelling-in-comment)

Primer are costly, so if other job fails we cut them short I think.

[DanielNoord]

One nit about typing. Change itself looks good to resolve the current issue!

[Pierre-Sassoulas]

LGTM, thank you @timmartin !

[github-actions]

🤖 According to the primer, this change has no effect on the checked open source code. 🤖🎉

This comment was generated for commit bd612cf