Protect against AttributeError when checking cell-var-from-loop

Close #3646

Author: PCManticore

ChangeLog

@@ -32,6 +32,10 @@ Release date: TBA
 
   Close #3538
 
+* Protect against `AttributeError` when checking `cell-var-from-loop`
+
+  Close #3646
+
 
 What's New in Pylint 2.5.2?
 ===========================

pylint/checkers/variables.py

@@ -1716,13 +1716,14 @@ def _is_direct_lambda_call():
         else:
             assign_scope = assignment_node.scope()
             maybe_for = assignment_node
-            while not isinstance(maybe_for, astroid.For):
+            while maybe_for and not isinstance(maybe_for, astroid.For):
                 if maybe_for is assign_scope:
                     break
                 maybe_for = maybe_for.parent
             else:
                 if (
-                    maybe_for.parent_of(node_scope)
+                    maybe_for
+                    and maybe_for.parent_of(node_scope)
                     and not _is_direct_lambda_call()
                     and not isinstance(node_scope.statement(), astroid.Return)
                 ):

tests/functional/c/cellvar_escaping_loop.py

@@ -1,7 +1,10 @@
-# pylint: disable=print-statement, unnecessary-comprehension
+# pylint: disable=print-statement, unnecessary-comprehension,missing-docstring,too-few-public-methods
 """Tests for loopvar-in-closure."""
 from __future__ import print_function
 
+from enum import Enum
+
+
 def good_case():
     """No problems here."""
     lst = []
@@ -118,3 +121,11 @@ def bad_case6():
         print(j)
         lst.append(lambda: i)  # [cell-var-from-loop]
     return lst
+
+
+class Test(Enum):
+    TEST = (40, 160)
+
+    @staticmethod
+    def new_test(minimum=TEST[0], maximum=TEST[1]):
+        return minimum, maximum

tests/functional/c/cellvar_escaping_loop.txt

@@ -1,6 +1,6 @@
-cell-var-from-loop:67:bad_case.<lambda>:Cell variable i defined in loop
-cell-var-from-loop:72:bad_case2.<lambda>:Cell variable i defined in loop
-cell-var-from-loop:80:bad_case3.<lambda>:Cell variable j defined in loop
-cell-var-from-loop:90:bad_case4.nested:Cell variable i defined in loop
-cell-var-from-loop:111:bad_case5.<lambda>:Cell variable i defined in loop
-cell-var-from-loop:119:bad_case6.<lambda>:Cell variable i defined in loop
+cell-var-from-loop:70:bad_case.<lambda>:Cell variable i defined in loop
+cell-var-from-loop:75:bad_case2.<lambda>:Cell variable i defined in loop
+cell-var-from-loop:83:bad_case3.<lambda>:Cell variable j defined in loop
+cell-var-from-loop:93:bad_case4.nested:Cell variable i defined in loop
+cell-var-from-loop:114:bad_case5.<lambda>:Cell variable i defined in loop
+cell-var-from-loop:122:bad_case6.<lambda>:Cell variable i defined in loop