Add an exception for IndexError inside uninferable_final_decorator

ChangeLog

@@ -25,6 +25,8 @@ Release date: TBA
 
   Closes #4301
 
+* Fix ``IndexError`` crash in ``uninferable_final_decorators`` method.
+
 * By default the similarity checker will now ignore imports and ignore function signatures when computing
   duplication. If you want to keep the previous behaviour set ``ignore-imports`` and ``ignore-signatures`` to ``False``.
 

doc/whatsnew/2.14.rst

@@ -305,6 +305,8 @@ Other Changes
 * By default the similarity checker will now ignore imports and ignore function signatures when computing
   duplication. If you want to keep the previous behaviour set ``ignore-imports`` and ``ignore-signatures`` to ``False``.
 
+* Fix ``IndexError`` crash in ``uninferable_final_decorators`` method.
+
 * Pylint now expands the user path (i.e. ``~`` to ``home/yusef/``) and expands environment variables (i.e. ``home/$USER/$project``
   to ``home/yusef/pylint`` for ``USER=yusef`` and ``project=pylint``) for pyreverse's ``output-directory``,
   ``import-graph``, ``ext-import-graph``,  ``int-import-graph`` options, and the spell checker's ``spelling-private-dict-file``

pylint/checkers/utils.py

@@ -850,7 +850,7 @@ def uninferable_final_decorators(
         if isinstance(decorator, nodes.Attribute):
             try:
                 import_node = decorator.expr.lookup(decorator.expr.name)[1][0]
-            except AttributeError:
+            except (AttributeError, IndexError):
                 continue
         elif isinstance(decorator, nodes.Name):
             lookup_values = decorator.lookup(decorator.name)

tests/functional/r/regression/regression_6531_crash_index_error.py

@@ -0,0 +1,28 @@
+# pylint: disable=missing-docstring, redefined-outer-name
+
+import pytest
+
+
+class Wallet:
+    def __init__(self):
+        self.balance = 0
+
+    def add_cash(self, earned):
+        self.balance += earned
+
+    def spend_cash(self, spent):
+        self.balance -= spent
+
+@pytest.fixture
+def my_wallet():
+    '''Returns a Wallet instance with a zero balance'''
+    return Wallet()
+
+@pytest.mark.parametrize("earned,spent,expected", [
+    (30, 10, 20),
+    (20, 2, 18),
+])
+def test_transactions(my_wallet, earned, spent, expected):
+    my_wallet.add_cash(earned)
+    my_wallet.spend_cash(spent)
+    assert my_wallet.balance == expected