From 1a96f16401c7bf10d4873f54b02f7bbbf94f492d Mon Sep 17 00:00:00 2001
From: Ilya Konstantinov <ilya.konstantinov@gmail.com>
Date: Fri, 13 Jan 2023 09:29:38 -0500
Subject: [PATCH] Derive pytest.raises from AbstractContextManager

Makes `AbstractContextManager` the shared base class between "raises" and other context managers.

The motivation is for type checkers to narrow `pytest.raises(...) if x else nullcontext()` to a `ContextManager` rather than `object`.
---
 changelog/10660.bugfix.rst |  2 ++
 src/_pytest/python_api.py  |  4 ++--
 testing/typing_checks.py   | 11 +++++++++++
 3 files changed, 15 insertions(+), 2 deletions(-)
 create mode 100644 changelog/10660.bugfix.rst

diff --git a/changelog/10660.bugfix.rst b/changelog/10660.bugfix.rst
new file mode 100644
index 000000000..62e354941
--- /dev/null
+++ b/changelog/10660.bugfix.rst
@@ -0,0 +1,2 @@
+Fix :py:func:`pytest.raises` to return a 'ContextManager' so that type-checkers could narrow
+:code:`pytest.raises(...) if ... else nullcontext()` down to 'ContextManager' rather than 'object'.
diff --git a/src/_pytest/python_api.py b/src/_pytest/python_api.py
index ea45753cd..4bc934861 100644
--- a/src/_pytest/python_api.py
+++ b/src/_pytest/python_api.py
@@ -8,7 +8,7 @@ from types import TracebackType
 from typing import Any
 from typing import Callable
 from typing import cast
-from typing import Generic
+from typing import ContextManager
 from typing import List
 from typing import Mapping
 from typing import Optional
@@ -957,7 +957,7 @@ raises.Exception = fail.Exception  # type: ignore
 
 
 @final
-class RaisesContext(Generic[E]):
+class RaisesContext(ContextManager[_pytest._code.ExceptionInfo[E]]):
     def __init__(
         self,
         expected_exception: Union[Type[E], Tuple[Type[E], ...]],
diff --git a/testing/typing_checks.py b/testing/typing_checks.py
index 0a6b5ad28..d15b3988b 100644
--- a/testing/typing_checks.py
+++ b/testing/typing_checks.py
@@ -3,6 +3,11 @@
 This file is not executed, it is only checked by mypy to ensure that
 none of the code triggers any mypy errors.
 """
+import contextlib
+from typing import Optional
+
+from typing_extensions import assert_type
+
 import pytest
 
 
@@ -22,3 +27,9 @@ def check_fixture_ids_callable() -> None:
 @pytest.mark.parametrize("func", [str, int], ids=lambda x: str(x.__name__))
 def check_parametrize_ids_callable(func) -> None:
     pass
+
+
+def check_raises_is_a_context_manager(val: bool) -> None:
+    with pytest.raises(RuntimeError) if val else contextlib.nullcontext() as excinfo:
+        pass
+    assert_type(excinfo, Optional[pytest.ExceptionInfo[RuntimeError]])