From ae86e1d91d64c52f0db583ea2444cdcfb5472a92 Mon Sep 17 00:00:00 2001
From: Thomas Grainger <tagrain@gmail.com>
Date: Sun, 29 Dec 2024 12:46:15 +0000
Subject: [PATCH 01/11] collapse exceptions groups from streaming response

---
 starlette/responses.py | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/starlette/responses.py b/starlette/responses.py
index 31874f655..c522e7f23 100644
--- a/starlette/responses.py
+++ b/starlette/responses.py
@@ -18,6 +18,7 @@
 import anyio
 import anyio.to_thread
 
+from starlette._utils import collapse_excgroups
 from starlette.background import BackgroundTask
 from starlette.concurrency import iterate_in_threadpool
 from starlette.datastructures import URL, Headers, MutableHeaders
@@ -258,14 +259,15 @@ async def __call__(self, scope: Scope, receive: Receive, send: Send) -> None:
             except OSError:
                 raise ClientDisconnect()
         else:
-            async with anyio.create_task_group() as task_group:
+            with collapse_excgroups():
+                async with anyio.create_task_group() as task_group:
 
-                async def wrap(func: typing.Callable[[], typing.Awaitable[None]]) -> None:
-                    await func()
-                    task_group.cancel_scope.cancel()
+                    async def wrap(func: typing.Callable[[], typing.Awaitable[None]]) -> None:
+                        await func()
+                        task_group.cancel_scope.cancel()
 
-                task_group.start_soon(wrap, partial(self.stream_response, send))
-                await wrap(partial(self.listen_for_disconnect, receive))
+                    task_group.start_soon(wrap, partial(self.stream_response, send))
+                    await wrap(partial(self.listen_for_disconnect, receive))
 
         if self.background is not None:
             await self.background()

From a4687d7c5fce21a164925629838b5bccf4f3acdd Mon Sep 17 00:00:00 2001
From: Thomas Grainger <tagrain@gmail.com>
Date: Sun, 29 Dec 2024 14:08:08 +0000
Subject: [PATCH 02/11] collapse only one level of excg

---
 starlette/_utils.py           | 29 +++++++++++++++++++++--------
 tests/middleware/test_base.py | 17 +++++++++++++----
 2 files changed, 34 insertions(+), 12 deletions(-)

diff --git a/starlette/_utils.py b/starlette/_utils.py
index 0c389dcb2..e93250163 100644
--- a/starlette/_utils.py
+++ b/starlette/_utils.py
@@ -13,12 +13,14 @@
 else:  # pragma: no cover
     from typing_extensions import TypeGuard
 
-has_exceptiongroups = True
 if sys.version_info < (3, 11):  # pragma: no cover
     try:
         from exceptiongroup import BaseExceptionGroup  # type: ignore[unused-ignore,import-not-found]
     except ImportError:
-        has_exceptiongroups = False
+
+        class BaseExceptionGroup(BaseException):  # type: ignore[no-redef]
+            pass
+
 
 T = typing.TypeVar("T")
 AwaitableCallable = typing.Callable[..., typing.Awaitable[T]]
@@ -74,12 +76,23 @@ async def __aexit__(self, *args: typing.Any) -> None | bool:
 def collapse_excgroups() -> typing.Generator[None, None, None]:
     try:
         yield
-    except BaseException as exc:
-        if has_exceptiongroups:  # pragma: no cover
-            while isinstance(exc, BaseExceptionGroup) and len(exc.exceptions) == 1:
-                exc = exc.exceptions[0]
-
-        raise exc
+    except BaseExceptionGroup as excs:
+        if len(excs.exceptions) != 1:
+            raise
+
+        exc = excs.exceptions[0]
+        context = exc.__context__
+        tb = exc.__traceback__
+        cause = exc.__cause__
+        sc = exc.__suppress_context__
+        try:
+            raise exc
+        finally:
+            exc.__traceback__ = tb
+            exc.__context__ = context
+            exc.__cause__ = cause
+            exc.__suppress_context__ = sc
+            del exc, cause, tb, context
 
 
 def get_route_path(scope: Scope) -> str:
diff --git a/tests/middleware/test_base.py b/tests/middleware/test_base.py
index 7232cfd18..c2cecf48a 100644
--- a/tests/middleware/test_base.py
+++ b/tests/middleware/test_base.py
@@ -8,6 +8,7 @@
 import anyio
 import pytest
 from anyio.abc import TaskStatus
+from exceptiongroup import ExceptionGroup
 
 from starlette.applications import Starlette
 from starlette.background import BackgroundTask
@@ -41,6 +42,10 @@ def exc(request: Request) -> None:
     raise Exception("Exc")
 
 
+def eg(request: Request) -> None:
+    raise ExceptionGroup("my exception group", [ValueError("TEST")])
+
+
 def exc_stream(request: Request) -> StreamingResponse:
     return StreamingResponse(_generate_faulty_stream())
 
@@ -76,6 +81,7 @@ async def websocket_endpoint(session: WebSocket) -> None:
     routes=[
         Route("/", endpoint=homepage),
         Route("/exc", endpoint=exc),
+        Route("/eg", endpoint=eg),
         Route("/exc-stream", endpoint=exc_stream),
         Route("/no-response", endpoint=NoResponse),
         WebSocketRoute("/ws", endpoint=websocket_endpoint),
@@ -89,13 +95,16 @@ def test_custom_middleware(test_client_factory: TestClientFactory) -> None:
     response = client.get("/")
     assert response.headers["Custom-Header"] == "Example"
 
-    with pytest.raises(Exception) as ctx:
+    with pytest.raises(Exception) as ctx1:
         response = client.get("/exc")
-    assert str(ctx.value) == "Exc"
+    assert str(ctx1.value) == "Exc"
 
-    with pytest.raises(Exception) as ctx:
+    with pytest.raises(Exception) as ctx2:
         response = client.get("/exc-stream")
-    assert str(ctx.value) == "Faulty Stream"
+    assert str(ctx2.value) == "Faulty Stream"
+
+    with pytest.raises(ExceptionGroup, match=r"my exception group \(1 sub-exception\)"):
+        client.get("/eg")
 
     with pytest.raises(RuntimeError):
         response = client.get("/no-response")

From ffacdb260efe14eb32c271dcf2260ac7eaff2cf6 Mon Sep 17 00:00:00 2001
From: Thomas Grainger <tagrain@gmail.com>
Date: Sun, 29 Dec 2024 14:14:29 +0000
Subject: [PATCH 03/11] conditional import

---
 tests/middleware/test_base.py | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/tests/middleware/test_base.py b/tests/middleware/test_base.py
index c2cecf48a..03bde0b0a 100644
--- a/tests/middleware/test_base.py
+++ b/tests/middleware/test_base.py
@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 import contextvars
+import sys
 from collections.abc import AsyncGenerator, AsyncIterator, Generator
 from contextlib import AsyncExitStack
 from typing import Any
@@ -8,7 +9,6 @@
 import anyio
 import pytest
 from anyio.abc import TaskStatus
-from exceptiongroup import ExceptionGroup
 
 from starlette.applications import Starlette
 from starlette.background import BackgroundTask
@@ -22,6 +22,9 @@
 from starlette.websockets import WebSocket
 from tests.types import TestClientFactory
 
+if sys.version_info < (3, 11):
+    from exceptiongroup import ExceptionGroup
+
 
 class CustomMiddleware(BaseHTTPMiddleware):
     async def dispatch(

From 02c221f346ca2f007e843e48f85e854e24ba87be Mon Sep 17 00:00:00 2001
From: Thomas Grainger <tagrain@gmail.com>
Date: Sun, 29 Dec 2024 14:23:47 +0000
Subject: [PATCH 04/11] avoid direct use of collapse_excgroups

---
 starlette/_utils.py           | 11 ++++++++++-
 starlette/middleware/base.py  |  6 +++---
 starlette/middleware/wsgi.py  |  3 ++-
 starlette/responses.py        | 15 +++++++--------
 tests/middleware/test_wsgi.py |  3 +--
 5 files changed, 23 insertions(+), 15 deletions(-)

diff --git a/starlette/_utils.py b/starlette/_utils.py
index e93250163..ca28c6fa5 100644
--- a/starlette/_utils.py
+++ b/starlette/_utils.py
@@ -4,7 +4,9 @@
 import functools
 import sys
 import typing
-from contextlib import contextmanager
+from contextlib import asynccontextmanager, contextmanager
+
+import anyio.abc
 
 from starlette.types import Scope
 
@@ -95,6 +97,13 @@ def collapse_excgroups() -> typing.Generator[None, None, None]:
             del exc, cause, tb, context
 
 
+@asynccontextmanager
+async def create_collapsing_task_group() -> typing.AsyncGenerator[anyio.abc.TaskGroup, None]:
+    with collapse_excgroups():
+        async with anyio.create_task_group() as tg:
+            yield tg
+
+
 def get_route_path(scope: Scope) -> str:
     path: str = scope["path"]
     root_path = scope.get("root_path", "")
diff --git a/starlette/middleware/base.py b/starlette/middleware/base.py
index 6e37c6f60..77404f790 100644
--- a/starlette/middleware/base.py
+++ b/starlette/middleware/base.py
@@ -4,7 +4,7 @@
 
 import anyio
 
-from starlette._utils import collapse_excgroups
+from starlette._utils import create_collapsing_task_group
 from starlette.requests import ClientDisconnect, Request
 from starlette.responses import AsyncContentStream, Response
 from starlette.types import ASGIApp, Message, Receive, Scope, Send
@@ -173,8 +173,8 @@ async def body_stream() -> typing.AsyncGenerator[bytes, None]:
             return response
 
         send_stream, recv_stream = anyio.create_memory_object_stream[Message]()
-        with recv_stream, send_stream, collapse_excgroups():
-            async with anyio.create_task_group() as task_group:
+        with recv_stream, send_stream:
+            async with create_collapsing_task_group() as task_group:
                 response = await self.dispatch_func(request, call_next)
                 await response(scope, wrapped_receive, send)
                 response_sent.set()
diff --git a/starlette/middleware/wsgi.py b/starlette/middleware/wsgi.py
index 6e0a3fae6..3e9ad0296 100644
--- a/starlette/middleware/wsgi.py
+++ b/starlette/middleware/wsgi.py
@@ -9,6 +9,7 @@
 import anyio
 from anyio.abc import ObjectReceiveStream, ObjectSendStream
 
+from starlette._utils import create_collapsing_task_group
 from starlette.types import Receive, Scope, Send
 
 warnings.warn(
@@ -102,7 +103,7 @@ async def __call__(self, receive: Receive, send: Send) -> None:
             more_body = message.get("more_body", False)
         environ = build_environ(self.scope, body)
 
-        async with anyio.create_task_group() as task_group:
+        async with create_collapsing_task_group() as task_group:
             task_group.start_soon(self.sender, send)
             async with self.stream_send:
                 await anyio.to_thread.run_sync(self.wsgi, environ, self.start_response)
diff --git a/starlette/responses.py b/starlette/responses.py
index c522e7f23..1f8b87bea 100644
--- a/starlette/responses.py
+++ b/starlette/responses.py
@@ -18,7 +18,7 @@
 import anyio
 import anyio.to_thread
 
-from starlette._utils import collapse_excgroups
+from starlette._utils import create_collapsing_task_group
 from starlette.background import BackgroundTask
 from starlette.concurrency import iterate_in_threadpool
 from starlette.datastructures import URL, Headers, MutableHeaders
@@ -259,15 +259,14 @@ async def __call__(self, scope: Scope, receive: Receive, send: Send) -> None:
             except OSError:
                 raise ClientDisconnect()
         else:
-            with collapse_excgroups():
-                async with anyio.create_task_group() as task_group:
+            async with create_collapsing_task_group() as task_group:
 
-                    async def wrap(func: typing.Callable[[], typing.Awaitable[None]]) -> None:
-                        await func()
-                        task_group.cancel_scope.cancel()
+                async def wrap(func: typing.Callable[[], typing.Awaitable[None]]) -> None:
+                    await func()
+                    task_group.cancel_scope.cancel()
 
-                    task_group.start_soon(wrap, partial(self.stream_response, send))
-                    await wrap(partial(self.listen_for_disconnect, receive))
+                task_group.start_soon(wrap, partial(self.stream_response, send))
+                await wrap(partial(self.listen_for_disconnect, receive))
 
         if self.background is not None:
             await self.background()
diff --git a/tests/middleware/test_wsgi.py b/tests/middleware/test_wsgi.py
index 3511c89c9..418f0946f 100644
--- a/tests/middleware/test_wsgi.py
+++ b/tests/middleware/test_wsgi.py
@@ -4,7 +4,6 @@
 
 import pytest
 
-from starlette._utils import collapse_excgroups
 from starlette.middleware.wsgi import WSGIMiddleware, build_environ
 from tests.types import TestClientFactory
 
@@ -86,7 +85,7 @@ def test_wsgi_exception(test_client_factory: TestClientFactory) -> None:
     # The HTTP protocol implementations would catch this error and return 500.
     app = WSGIMiddleware(raise_exception)
     client = test_client_factory(app)
-    with pytest.raises(RuntimeError), collapse_excgroups():
+    with pytest.raises(RuntimeError):
         client.get("/")
 
 

From c7c6206d10e64ae4947cafd9890e3b00929389c8 Mon Sep 17 00:00:00 2001
From: Thomas Grainger <tagrain@gmail.com>
Date: Sun, 29 Dec 2024 14:24:42 +0000
Subject: [PATCH 05/11] make private

---
 starlette/_utils.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/starlette/_utils.py b/starlette/_utils.py
index ca28c6fa5..2d6c70242 100644
--- a/starlette/_utils.py
+++ b/starlette/_utils.py
@@ -75,7 +75,7 @@ async def __aexit__(self, *args: typing.Any) -> None | bool:
 
 
 @contextmanager
-def collapse_excgroups() -> typing.Generator[None, None, None]:
+def _collapse_excgroups() -> typing.Generator[None, None, None]:
     try:
         yield
     except BaseExceptionGroup as excs:
@@ -99,7 +99,7 @@ def collapse_excgroups() -> typing.Generator[None, None, None]:
 
 @asynccontextmanager
 async def create_collapsing_task_group() -> typing.AsyncGenerator[anyio.abc.TaskGroup, None]:
-    with collapse_excgroups():
+    with _collapse_excgroups():
         async with anyio.create_task_group() as tg:
             yield tg
 

From 802409afe3e038856aa8e87543ecc902c5400231 Mon Sep 17 00:00:00 2001
From: Thomas Grainger <tagrain@gmail.com>
Date: Sun, 29 Dec 2024 14:43:44 +0000
Subject: [PATCH 06/11] remove incorrect mypy pin

---
 pyproject.toml | 1 -
 1 file changed, 1 deletion(-)

diff --git a/pyproject.toml b/pyproject.toml
index 95f195c50..223b6319f 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -68,7 +68,6 @@ combine-as-imports = true
 
 [tool.mypy]
 strict = true
-python_version = "3.9"
 
 [[tool.mypy.overrides]]
 module = "starlette.testclient.*"

From 5b43511fd25391e941d2e6a88dab0d94067017fb Mon Sep 17 00:00:00 2001
From: Thomas Grainger <tagrain@gmail.com>
Date: Sun, 29 Dec 2024 15:00:01 +0000
Subject: [PATCH 07/11] Update tests/middleware/test_base.py

---
 tests/middleware/test_base.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tests/middleware/test_base.py b/tests/middleware/test_base.py
index 03bde0b0a..483dd869e 100644
--- a/tests/middleware/test_base.py
+++ b/tests/middleware/test_base.py
@@ -22,7 +22,7 @@
 from starlette.websockets import WebSocket
 from tests.types import TestClientFactory
 
-if sys.version_info < (3, 11):
+if sys.version_info < (3, 11):  # pragma: no cover
     from exceptiongroup import ExceptionGroup
 
 

From 6500d2f8a8ab0c00c29dd608751100305a0686d2 Mon Sep 17 00:00:00 2001
From: Thomas Grainger <tagrain@gmail.com>
Date: Sun, 29 Dec 2024 14:45:14 +0000
Subject: [PATCH 08/11] remove unused ignore

---
 starlette/_utils.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/starlette/_utils.py b/starlette/_utils.py
index 2d6c70242..daa17d8c4 100644
--- a/starlette/_utils.py
+++ b/starlette/_utils.py
@@ -17,7 +17,7 @@
 
 if sys.version_info < (3, 11):  # pragma: no cover
     try:
-        from exceptiongroup import BaseExceptionGroup  # type: ignore[unused-ignore,import-not-found]
+        from exceptiongroup import BaseExceptionGroup
     except ImportError:
 
         class BaseExceptionGroup(BaseException):  # type: ignore[no-redef]

From 5e4a262623a085bc506f2ca280adb4b09a55c879 Mon Sep 17 00:00:00 2001
From: Thomas Grainger <tagrain@gmail.com>
Date: Sun, 29 Dec 2024 15:31:41 +0000
Subject: [PATCH 09/11] add coverage for collapsing

---
 tests/test__utils.py | 34 +++++++++++++++++++++++++++++++++-
 1 file changed, 33 insertions(+), 1 deletion(-)

diff --git a/tests/test__utils.py b/tests/test__utils.py
index 916f460d4..e4652ff1b 100644
--- a/tests/test__utils.py
+++ b/tests/test__utils.py
@@ -1,11 +1,15 @@
 import functools
+import sys
 from typing import Any
 
 import pytest
 
-from starlette._utils import get_route_path, is_async_callable
+from starlette._utils import create_collapsing_task_group, get_route_path, is_async_callable
 from starlette.types import Scope
 
+if sys.version_info < (3, 11):  # pragma: no cover
+    from exceptiongroups import ExceptionGroup
+
 
 def test_async_func() -> None:
     async def async_func() -> None: ...  # pragma: no cover
@@ -94,3 +98,31 @@ async def async_func(
 )
 def test_get_route_path(scope: Scope, expected_result: str) -> None:
     assert get_route_path(scope) == expected_result
+
+
+@pytest.mark.anyio
+async def test_collapsing_task_group_one_exc() -> None:
+    class MyException(Exception):
+        pass
+
+    with pytest.raises(MyException):
+        async with create_collapsing_task_group():
+            raise MyException
+
+
+@pytest.mark.anyio
+async def test_collapsing_task_group_two_exc() -> None:
+    class MyException(Exception):
+        pass
+
+    async def raise_exc() -> None:
+        raise MyException
+
+    with pytest.raises(ExceptionGroup) as exc:
+        async with create_collapsing_task_group() as task_group:
+            task_group.start_soon(raise_exc)
+            raise MyException
+
+    exc1, exc2 = exc.value.exceptions
+    assert isinstance(exc1, MyException)
+    assert isinstance(exc2, MyException)

From e44b25429e83d7817c9e63ce53fa770ef8be72c2 Mon Sep 17 00:00:00 2001
From: Thomas Grainger <tagrain@gmail.com>
Date: Sun, 29 Dec 2024 15:33:30 +0000
Subject: [PATCH 10/11] optimize

---
 starlette/_utils.py | 16 +++++-----------
 1 file changed, 5 insertions(+), 11 deletions(-)

diff --git a/starlette/_utils.py b/starlette/_utils.py
index daa17d8c4..143c660f3 100644
--- a/starlette/_utils.py
+++ b/starlette/_utils.py
@@ -4,7 +4,7 @@
 import functools
 import sys
 import typing
-from contextlib import asynccontextmanager, contextmanager
+from contextlib import asynccontextmanager
 
 import anyio.abc
 
@@ -74,10 +74,11 @@ async def __aexit__(self, *args: typing.Any) -> None | bool:
         return None
 
 
-@contextmanager
-def _collapse_excgroups() -> typing.Generator[None, None, None]:
+@asynccontextmanager
+async def create_collapsing_task_group() -> typing.AsyncGenerator[anyio.abc.TaskGroup, None]:
     try:
-        yield
+        async with anyio.create_task_group() as tg:
+            yield tg
     except BaseExceptionGroup as excs:
         if len(excs.exceptions) != 1:
             raise
@@ -97,13 +98,6 @@ def _collapse_excgroups() -> typing.Generator[None, None, None]:
             del exc, cause, tb, context
 
 
-@asynccontextmanager
-async def create_collapsing_task_group() -> typing.AsyncGenerator[anyio.abc.TaskGroup, None]:
-    with _collapse_excgroups():
-        async with anyio.create_task_group() as tg:
-            yield tg
-
-
 def get_route_path(scope: Scope) -> str:
     path: str = scope["path"]
     root_path = scope.get("root_path", "")

From e24198f2832ea1edb0b4ed6e6708aa6f9f4bd463 Mon Sep 17 00:00:00 2001
From: Thomas Grainger <tagrain@gmail.com>
Date: Sun, 29 Dec 2024 15:47:00 +0000
Subject: [PATCH 11/11] Update tests/test__utils.py

---
 tests/test__utils.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tests/test__utils.py b/tests/test__utils.py
index e4652ff1b..60af81392 100644
--- a/tests/test__utils.py
+++ b/tests/test__utils.py
@@ -8,7 +8,7 @@
 from starlette.types import Scope
 
 if sys.version_info < (3, 11):  # pragma: no cover
-    from exceptiongroups import ExceptionGroup
+    from exceptiongroup import ExceptionGroup
 
 
 def test_async_func() -> None: