From 407d9841428f037e0ada71f7ca028f7d1171c6db Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Cl=C3=A9ment=20Robert?= <cr52@protonmail.com>
Date: Tue, 30 Jan 2024 16:20:30 +0100
Subject: [PATCH] Fix an edge case where ExceptionInfo._stringify_exception
 could crash pytest.raises (#11879)

Co-authored-by: Bruno Oliveira <bruno@soliv.dev>
Co-authored-by: Zac Hatfield-Dodds <zac.hatfield.dodds@gmail.com>
---
 AUTHORS                    |  1 +
 changelog/11879.bugfix.rst |  1 +
 src/_pytest/_code/code.py  | 13 ++++++++++++-
 testing/python/raises.py   | 13 +++++++++++++
 4 files changed, 27 insertions(+), 1 deletion(-)
 create mode 100644 changelog/11879.bugfix.rst

diff --git a/AUTHORS b/AUTHORS
index bea582046..879097622 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -93,6 +93,7 @@ Christopher Dignam
 Christopher Gilling
 Claire Cecil
 Claudio Madotto
+Clément M.T. Robert
 CrazyMerlyn
 Cristian Vera
 Cyrus Maden
diff --git a/changelog/11879.bugfix.rst b/changelog/11879.bugfix.rst
new file mode 100644
index 000000000..70b6cce72
--- /dev/null
+++ b/changelog/11879.bugfix.rst
@@ -0,0 +1 @@
+Fix an edge case where ``ExceptionInfo._stringify_exception`` could crash :func:`pytest.raises`.
diff --git a/src/_pytest/_code/code.py b/src/_pytest/_code/code.py
index d99b52366..39bbc3c14 100644
--- a/src/_pytest/_code/code.py
+++ b/src/_pytest/_code/code.py
@@ -699,10 +699,21 @@ class ExceptionInfo(Generic[E]):
         return fmt.repr_excinfo(self)
 
     def _stringify_exception(self, exc: BaseException) -> str:
+        try:
+            notes = getattr(exc, "__notes__", [])
+        except KeyError:
+            # Workaround for https://github.com/python/cpython/issues/98778 on
+            # Python <= 3.9, and some 3.10 and 3.11 patch versions.
+            HTTPError = getattr(sys.modules.get("urllib.error", None), "HTTPError", ())
+            if sys.version_info[:2] <= (3, 11) and isinstance(exc, HTTPError):
+                notes = []
+            else:
+                raise
+
         return "\n".join(
             [
                 str(exc),
-                *getattr(exc, "__notes__", []),
+                *notes,
             ]
         )
 
diff --git a/testing/python/raises.py b/testing/python/raises.py
index 47b22f28a..369a66a9f 100644
--- a/testing/python/raises.py
+++ b/testing/python/raises.py
@@ -302,3 +302,16 @@ class TestRaises:
             with pytest.raises(("hello", NotAnException)):  # type: ignore[arg-type]
                 pass  # pragma: no cover
         assert "must be a BaseException type, not str" in str(excinfo.value)
+
+    def test_issue_11872(self) -> None:
+        """Regression test for #11872.
+
+        urllib.error.HTTPError on Python<=3.9 raises KeyError instead of
+        AttributeError on invalid attribute access.
+
+        https://github.com/python/cpython/issues/98778
+        """
+        from urllib.error import HTTPError
+
+        with pytest.raises(HTTPError, match="Not Found"):
+            raise HTTPError(code=404, msg="Not Found", fp=None, hdrs=None, url="")  # type: ignore [arg-type]