Add deprecation warning when HTTPException is returned instead of raised

CHANGES/2415.removal

@@ -0,0 +1 @@
+Add DeprecationWarning for returning HTTPException

CONTRIBUTORS.txt

@@ -140,6 +140,7 @@ Nicolas Braem
 Nikolay Novik
 Olaf Conradi
 Pahaz Blinov
+Panagiotis Kolokotronis
 Pankaj Pandey
 Pau Freixes
 Paul Colomiets

aiohttp/web_protocol.py

@@ -3,6 +3,7 @@
 import http.server
 import socket
 import traceback
+import warnings
 from collections import deque
 from contextlib import suppress
 from html import escape as html_escape
@@ -427,6 +428,14 @@ async def start(self, message, payload, handler):
                 if self.access_log:
                     self.log_access(request, resp, loop.time() - now)
 
+                # Deprication warning (See #2415)
+                if isinstance(resp, HTTPException):
+                    warnings.warn(
+                        "returning HTTPException object is deprecated (#2415) "
+                        "and will be removed, "
+                        "please raise the exception instead",
+                        DeprecationWarning)
+
                 # check payload
                 if not payload.is_eof():
                     lingering_time = self._lingering_time

docs/web_quickstart.rst

@@ -590,6 +590,11 @@ The exceptions are also a subclass of :class:`Response`, allowing you to either
 ``raise`` or ``return`` them in a
 :ref:`request handler <aiohttp-web-handler>` for the same effect.
 
+.. warning::
+
+   Returning :class:`~HTTPException` or its subclasses is deprecated and will
+   be removed in subsequent aiohttp versions.
+
 The following snippets are the same::
 
     async def handler(request):

tests/test_web_functional.py

@@ -1576,3 +1576,16 @@ async def handler(request):
     async with aiohttp.ClientSession(loop=loop) as session:
         async with session.post(server.make_url('/'), data=data) as resp:
             assert resp.status == 200
+
+
+async def test_return_http_exception_deprecated(loop, test_client):
+
+    async def handler(request):
+        return web.HTTPForbidden()
+
+    app = web.Application()
+    app.router.add_route('GET', '/', handler)
+    client = await test_client(app)
+
+    with pytest.warns(DeprecationWarning):
+        await client.get('/')