Fix #5112: Prevent used-before-assignment if named expression found first in container

[jacobtylerwalls]

Type of Changes

	Type
✓	🐛 Bug fix

Description

Prevent a false positive for used-before-assignment when a named expression (walrus operator) is found first in a container.

For instance, this passed:

assert (x := True)

But this didn't (it's a tuple):

assert (x := True), x

Notice this should not pass:

assert x, (x := True)

Closes #5112

Of course, this can wait for 2.14, no problem.

[coveralls]

Pull Request Test Coverage Report for Build 1860771448

• 12 of 12 (100.0%) changed or added relevant lines in 1 file are covered.
• 26 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.009%) to 93.982%

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Files with Coverage Reduction	New Missed Lines	%
pylint/lint/parallel.py	2	92.86%
pylint/checkers/variables.py	24	96.44%

Totals
Change from base Build 1840800912:	-0.009%
Covered Lines:	14929
Relevant Lines:	15885

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💛 - Coveralls

[Pierre-Sassoulas]

I don't know about where to put this. On one hand this is a bug fix, it feels wrong not to put it in if the work is done. On the other hand we have a LOT of thing in 2.13 already and we need to focus on actually releasing at some point. We can probably put this in 2.13 as I took the time to review now.

[Pierre-Sassoulas]

There's been a new issue opened regarding this problem, I think we could add this regression test, what do you think ?

[Pierre-Sassoulas]

Sounds good to me.

[DanielNoord]

Pff... Man that's convoluted. Can't we raise an don't-write-code-like-this warning here? 😅

[Pierre-Sassoulas]

Haha, I had to take 2-3mn and run the code to understand myself 😄 But do we really want to make the kind of person that would write this, flock to our bug tracker to complain 😉 ?