Fix class scope issues in undefined-variable checker #511 #1976 #3494

[anjsimmo]

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Description

The _ignore_class_scope method within the variable checker determines whether to search attributes in the class scope. This in turn uses _defined_in_function_definition to distinguish function arguments and annotations from the contents of the function (which form their own scope). However, _defined_in_function_definition was previously missing checks to search decorators (#511) and return type annotations (#1976), leading to false positives. These two checks were an easy fix.

While implementing the solution, it became apparent that Pylint wasn't checking whether variables inside list/set/dict comprehensions and generator expressions could actually access class scope. This led to false negatives where Python would raise a NameError, but Pylint wasn't providing any warning (#3494). A new function _in_lambda_or_comprehension_body was added that begins with a variable node, then searches up its parent chain, checking for lambda expressions and comprehensions along the way that would cause class attributes to go out of scope. Only the lambda arguments, and comprehension iters are allowed to pass through.

tests/functional/c/class_scope.py was changed to note that lambda arg=revattr: revattr * 42 uses revattr as both an argument, as well as an undefined-variable in the body. An additional line was also added to test the scope issues were addressed for generator expressions.

Type of Changes

	Type
✓	🐛 Bug fix

Related Issue

Closes #511
Closes #1976
Closes #3494

[coveralls]

Coverage decreased (-0.01%) to 90.442% when pulling 34b0abd on anjsimmo:fix-undefined-variable-scoping into 67d0572 on PyCQA:master.

[PCManticore]

Hey @anjsimmo This is a fantastic patch, thanks a lot for sending it in! I don't have any comments since it was clear and straightforward. Thanks for squashing 3 bugs all at once.