From 78fb97105f38dc286353bbc331a243b6e753fe3c Mon Sep 17 00:00:00 2001
From: Petr Viktorin <encukou@gmail.com>
Date: Wed, 6 Jan 2021 13:33:33 +0100
Subject: [PATCH 1/2] Make code.FormattedExcinfo.get_source more defensive

When line_index was a large negative number, get_source failed
on `source.lines[line_index]`.
Use the same dummy Source as with a large positive line_index.
---
 src/_pytest/_code/code.py | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/_pytest/_code/code.py b/src/_pytest/_code/code.py
index b852175606..af3bdf0561 100644
--- a/src/_pytest/_code/code.py
+++ b/src/_pytest/_code/code.py
@@ -721,11 +721,11 @@ def get_source(
     ) -> List[str]:
         """Return formatted and marked up source lines."""
         lines = []
-        if source is None or line_index >= len(source.lines):
+        if source is not None and line_index < 0:
+            line_index += len(source.lines)
+        if source is None or line_index >= len(source.lines) or line_index < 0:
             source = Source("???")
             line_index = 0
-        if line_index < 0:
-            line_index += len(source)
         space_prefix = "    "
         if short:
             lines.append(space_prefix + source.lines[line_index].strip())

From 0a75c8e57b4b87ee533f3b08612590704b6743bb Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Miro=20Hron=C4=8Dok?= <miro@hroncok.cz>
Date: Thu, 22 Apr 2021 19:13:44 +0200
Subject: [PATCH 2/2] Add a regression test for a more defensive
 code.FormattedExcinfo.get_source

---
 testing/code/test_excinfo.py | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/testing/code/test_excinfo.py b/testing/code/test_excinfo.py
index e6a9cbaf73..287733dac7 100644
--- a/testing/code/test_excinfo.py
+++ b/testing/code/test_excinfo.py
@@ -1397,6 +1397,29 @@ def test(tmp_path):
     result.stderr.no_fnmatch_line("*INTERNALERROR*")
 
 
+def test_regression_nagative_line_index(pytester):
+    """
+    With Python 3.10 alphas, there was an INTERNALERROR reported in
+    https://github.com/pytest-dev/pytest/pull/8227
+    This test ensures it does not regress.
+    """
+    pytester.makepyfile(
+        """
+        import ast
+        import pytest
+
+
+        def test_literal_eval():
+            with pytest.raises(ValueError, match="^$"):
+                ast.literal_eval("pytest")
+    """
+    )
+    result = pytester.runpytest()
+    result.stdout.fnmatch_lines(["* 1 failed in *"])
+    result.stdout.no_fnmatch_line("*INTERNALERROR*")
+    result.stderr.no_fnmatch_line("*INTERNALERROR*")
+
+
 @pytest.mark.usefixtures("limited_recursion_depth")
 def test_exception_repr_extraction_error_on_recursion():
     """