[3.8] Backport fix for setting cookies

CHANGES/5233.bugfix

@@ -0,0 +1 @@
+Fix cookies disappearing from HTTPExceptions.

aiohttp/web_protocol.py

@@ -426,6 +426,7 @@ async def _handle_request(
             resp = Response(
                 status=exc.status, reason=exc.reason, text=exc.text, headers=exc.headers
             )
+            resp._cookies = exc._cookies
             reset = await self.finish_response(request, resp, start_time)
         except asyncio.CancelledError:
             raise

tests/test_web_exceptions.py

@@ -203,3 +203,31 @@ def test_HTTPException_retains_cause() -> None:
     tb = "".join(format_exception(ei.type, ei.value, ei.tb))
     assert "CustomException" in tb
     assert "direct cause" in tb
+
+
+async def test_HTTPException_retains_cookie(aiohttp_client):
+    @web.middleware
+    async def middleware(request, handler):
+        try:
+            return await handler(request)
+        except web.HTTPException as exc:
+            exc.set_cookie("foo", request["foo"])
+            raise exc
+
+    async def save(request):
+        request["foo"] = "works"
+        raise web.HTTPFound("/show")
+
+    async def show(request):
+        return web.Response(text=request.cookies["foo"])
+
+    app = web.Application(middlewares=[middleware])
+    app.router.add_route("GET", "/save", save)
+    app.router.add_route("GET", "/show", show)
+    client = await aiohttp_client(app)
+
+    resp = await client.get("/save")
+    assert resp.status == 200
+    assert str(resp.url)[-5:] == "/show"
+    text = await resp.text()
+    assert text == "works"