Fix #1993: Deprecate registering synchronous web handlers

aiohttp/web_urldispatcher.py

@@ -107,6 +107,9 @@ def __init__(self, method, handler, *,
               issubclass(handler, AbstractView)):
             pass
         else:
+            warnings.warn("Bare functions are deprecated, "
+                          "use async ones", DeprecationWarning)
+
             @wraps(handler)
             @asyncio.coroutine
             def handler_wrapper(*args, **kwargs):

changes/1993.feature

@@ -0,0 +1 @@
+Deprecate registering synchronous web handlers

tests/test_urldispatch.py

@@ -1049,3 +1049,11 @@ def test_convert_empty_path_to_slash_on_freezing(router):
     assert resource.get_info() == {'path': ''}
     router.freeze()
     assert resource.get_info() == {'path': '/'}
+
+
+def test_deprecate_non_coroutine(router):
+    def handler(request):
+        pass
+
+    with pytest.warns(DeprecationWarning):
+        router.add_route('GET', '/handler', handler)