[fix] unnecessary-dict-index-lookup for in-loop deletion of an index from enumerate (#10628)

Closes #10627

Author: Pierre-Sassoulas

doc/whatsnew/fragments/10627.bugfix

@@ -0,0 +1,4 @@
+Fixed a crash in :ref:`unnecessary-dict-index-lookup` when the index of an enumerated list
+was deleted inside a for loop.
+
+Closes #10627

pylint/checkers/refactoring/refactoring_checker.py

@@ -2358,7 +2358,8 @@ def _check_unnecessary_list_index_lookup(
 
                     if (
                         isinstance(node, nodes.For)
-                        and index.lookup(index.name)[1][-1].lineno > node.lineno
+                        and (lookup_results := index.lookup(index.name)[1])
+                        and lookup_results[-1].lineno > node.lineno
                     ):
                         # Ignore this subscript if it has been redefined after
                         # the for loop.

tests/functional/r/regression_02/regression_10627.py

@@ -0,0 +1,8 @@
+"""Test for deleted index."""
+
+# pylint: disable=missing-function-docstring
+
+def test_deleted_index(letters: list[str]) -> None:
+    for index, letter in enumerate(letters): # [unused-variable]
+        del index
+        print(letters[index]) # [unnecessary-list-index-lookup]

tests/functional/r/regression_02/regression_10627.txt

@@ -0,0 +1,2 @@
+unused-variable:6:15:6:21:test_deleted_index:Unused variable 'letter':UNDEFINED
+unnecessary-list-index-lookup:8:14:8:28:test_deleted_index:Unnecessary list index lookup, use 'letter' instead:HIGH