Fix crash on unbalanced tuple unpacking

Author: jacobtylerwalls

ChangeLog

@@ -36,6 +36,9 @@ What's New in Pylint 2.13.3?
 ============================
 Release date: TBA
 
+* Fix crash involving unbalanced tuple unpacking.
+
+  Closes #5998
 
 
 What's New in Pylint 2.13.2?

pylint/checkers/base/name_checker/checker.py

@@ -386,6 +386,8 @@ def visit_assignname(self, node: nodes.AssignName) -> None:
                 elif (
                     isinstance(node.parent, nodes.Tuple)
                     and isinstance(assign_type.value, nodes.Tuple)
+                    # protect against unbalanced tuple unpacking
+                    and node.parent.elts.index(node) < len(assign_type.value.elts)
                     and self._assigns_typevar(
                         assign_type.value.elts[node.parent.elts.index(node)]
                     )

tests/functional/u/unbalanced_tuple_unpacking.py

@@ -157,3 +157,6 @@ def my_function(mystring):
 a, b = my_function("12")  # [unbalanced-tuple-unpacking]
 c = my_function("12")
 d, *_ = my_function("12")
+
+# https://github.com/PyCQA/pylint/issues/5998
+x, y, z = (1, 2)  # [unbalanced-tuple-unpacking]

tests/functional/u/unbalanced_tuple_unpacking.txt

@@ -6,3 +6,4 @@ unbalanced-tuple-unpacking:96:8:96:33:UnbalancedUnpacking.test:"Possible unbalan
 unbalanced-tuple-unpacking:140:8:140:43:MyClass.sum_unpack_3_into_4:"Possible unbalanced tuple unpacking with sequence defined at line 128: left side has 4 label(s), right side has 3 value(s)":UNDEFINED
 unbalanced-tuple-unpacking:145:8:145:28:MyClass.sum_unpack_3_into_2:"Possible unbalanced tuple unpacking with sequence defined at line 128: left side has 2 label(s), right side has 3 value(s)":UNDEFINED
 unbalanced-tuple-unpacking:157:0:157:24::"Possible unbalanced tuple unpacking with sequence defined at line 151: left side has 2 label(s), right side has 0 value(s)":UNDEFINED
+unbalanced-tuple-unpacking:162:0:162:16::"Possible unbalanced tuple unpacking with sequence (1, 2): left side has 3 label(s), right side has 2 value(s)":UNDEFINED