From c3e257925e313a19f42dd17d20179152f5f5db2f Mon Sep 17 00:00:00 2001
From: "github-actions[bot]"
 <41898282+github-actions[bot]@users.noreply.github.com>
Date: Thu, 6 Jun 2024 22:03:21 +0000
Subject: [PATCH] [unnecessary-list-index-lookup] Fix crashes for uninferrable
 'start' value in 'enumerate' (#9704) (#9707)
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---------

Co-authored-by: Daniël van Noord <13665637+DanielNoord@users.noreply.github.com>
(cherry picked from commit 9f8dcbd6a9d37d56a14b747b83d97d6b8527a2ab)

Co-authored-by: Pierre Sassoulas <pierre.sassoulas@gmail.com>
---
 doc/whatsnew/fragments/9078.bugfix                    |  4 ++++
 pylint/checkers/refactoring/refactoring_checker.py    |  4 +++-
 .../u/unnecessary/unnecessary_list_index_lookup.py    | 11 +++++++++++
 3 files changed, 18 insertions(+), 1 deletion(-)
 create mode 100644 doc/whatsnew/fragments/9078.bugfix

diff --git a/doc/whatsnew/fragments/9078.bugfix b/doc/whatsnew/fragments/9078.bugfix
new file mode 100644
index 0000000000..2e48abc887
--- /dev/null
+++ b/doc/whatsnew/fragments/9078.bugfix
@@ -0,0 +1,4 @@
+Fixed a crash when the ``start`` value in an ``enumerate`` was non-constant and impossible to infer
+(like in``enumerate(apples, start=int(random_apple_index)``) for ``unnecessary-list-index-lookup``.
+
+Closes #9078
diff --git a/pylint/checkers/refactoring/refactoring_checker.py b/pylint/checkers/refactoring/refactoring_checker.py
index 9ffcecce12..a8bce74854 100644
--- a/pylint/checkers/refactoring/refactoring_checker.py
+++ b/pylint/checkers/refactoring/refactoring_checker.py
@@ -2454,7 +2454,9 @@ def _get_start_value(self, node: nodes.NodeNG) -> tuple[int | None, Confidence]:
             and isinstance(node.operand, (nodes.Attribute, nodes.Name))
         ):
             inferred = utils.safe_infer(node)
-            start_val = inferred.value if inferred else None
+            # inferred can be an astroid.base.Instance as in 'enumerate(x, int(y))' or
+            # not correctly inferred (None)
+            start_val = inferred.value if isinstance(inferred, nodes.Const) else None
             return start_val, INFERENCE
         if isinstance(node, nodes.UnaryOp):
             return node.operand.value, HIGH
diff --git a/tests/functional/u/unnecessary/unnecessary_list_index_lookup.py b/tests/functional/u/unnecessary/unnecessary_list_index_lookup.py
index 3201d5407d..b9f8b73251 100644
--- a/tests/functional/u/unnecessary/unnecessary_list_index_lookup.py
+++ b/tests/functional/u/unnecessary/unnecessary_list_index_lookup.py
@@ -156,3 +156,14 @@ def _get_extra_attrs(self, extra_columns):
 for idx, val in enumerate(my_list):
     if (val := 42) and my_list[idx] == 'b':
         print(1)
+
+def regression_9078(apples, cant_infer_this):
+    """Regression test for https://github.com/pylint-dev/pylint/issues/9078."""
+    for _, _ in enumerate(apples, int(cant_infer_this)):
+        ...
+
+def random_uninferrable_start(pears):
+    import random # pylint: disable=import-outside-toplevel
+
+    for _, _ in enumerate(pears, random.choice([5, 42])):
+        ...