Fix stacklevel in _CoroGuard's warning (#2125)

Fixes #2106

CONTRIBUTORS.txt

@@ -77,6 +77,7 @@ Gregory Haynes
 Günther Jena
 Hu Bo
 Hugo Herter
+Hynek Schlawack
 Igor Davydenko
 Igor Pavlov
 Ingmar Steen

aiohttp/helpers.py

@@ -106,6 +106,11 @@ def __await__(self):
 
 
 class _CoroGuard(_BaseCoroMixin):
+    """Only to be used with func:`deprecated_noop`.
+
+    Otherwise the stack information in the raised warning doesn't line up with
+    the user's code anymore.
+    """
     __slots__ = ('_msg', '_awaited')
 
     def __init__(self, coro, msg):
@@ -126,7 +131,7 @@ def __await__(self):
     def __del__(self):
         self._coro = None
         if not self._awaited:
-            warnings.warn(self._msg, DeprecationWarning)
+            warnings.warn(self._msg, DeprecationWarning, stacklevel=2)
 
 
 coroutines = asyncio.coroutines

changes/2106.bugfix

@@ -0,0 +1 @@
+Warnings about unawaited coroutines now correctly point to the user's code.

tests/test_client_session.py

@@ -64,9 +64,12 @@ def test_close_coro(create_session, loop):
 def test_close_deprecated(create_session):
     session = create_session()
 
-    with pytest.warns(DeprecationWarning):
+    with pytest.warns(DeprecationWarning) as ctx:
         session.close()
 
+    # Assert the warning points at us and not at _CoroGuard.
+    assert ctx.list[0].filename == __file__
+
 
 def test_init_headers_simple_dict(create_session):
     session = create_session(headers={"h1": "header1",

tests/test_helpers.py

@@ -17,7 +17,12 @@
 def test_warn():
     with pytest.warns(DeprecationWarning) as ctx:
         helpers.deprecated_noop('Text')
-    assert str(ctx.list[0].message) == 'Text'
+
+    w = ctx.list[0]
+
+    assert str(w.message) == 'Text'
+    # Assert the warning points at us and not at _CoroGuard.
+    assert w.filename == __file__
 
 
 @asyncio.coroutine