bpo-32591: Add native coroutine origin tracking (#5250)

* Add coro.cr_origin and sys.set_coroutine_origin_tracking_depth
* Use coroutine origin information in the unawaited coroutine warning
* Stop using set_coroutine_wrapper in asyncio debug mode
* In BaseEventLoop.set_debug, enable debugging in the correct thread

20 files changed, 485 insertions, 100 deletions

diff --git a/Doc/library/inspect.rst b/Doc/library/inspect.rst
index 6be28a2..147e802 100644
--- a/Doc/library/inspect.rst
+++ b/Doc/library/inspect.rst
@@ -34,6 +34,9 @@ provided as convenient choices for the second argument to :func:`getmembers`.
 They also help you determine when you can expect to find the following special
 attributes:
 
+.. this function name is too big to fit in the ascii-art table below
+.. |coroutine-origin-link| replace:: :func:`sys.set_coroutine_origin_tracking_depth`
+
 +-----------+-------------------+---------------------------+
 | Type      | Attribute         | Description               |
 +===========+===================+===========================+
@@ -215,6 +218,10 @@ attributes:
 +-----------+-------------------+---------------------------+
 |           | cr_code           | code                      |
 +-----------+-------------------+---------------------------+
+|           | cr_origin         | where coroutine was       |
+|           |                   | created, or ``None``. See |
+|           |                   | |coroutine-origin-link|   |
++-----------+-------------------+---------------------------+
 | builtin   | __doc__           | documentation string      |
 +-----------+-------------------+---------------------------+
 |           | __name__          | original name of this     |
@@ -234,6 +241,9 @@ attributes:
    The ``__name__`` attribute of generators is now set from the function
    name, instead of the code name, and it can now be modified.
 
+.. versionchanged:: 3.7
+
+   Add ``cr_origin`` attribute to coroutines.
 
 .. function:: getmembers(object[, predicate])
 
diff --git a/Doc/library/sys.rst b/Doc/library/sys.rst
index 957d02b..54281a3 100644
--- a/Doc/library/sys.rst
+++ b/Doc/library/sys.rst
@@ -675,6 +675,18 @@ always available.
       for details.)
 
 
+.. function:: get_coroutine_origin_tracking_depth()
+
+   Get the current coroutine origin tracking depth, as set by
+   func:`set_coroutine_origin_tracking_depth`.
+
+   .. versionadded:: 3.7
+
+   .. note::
+      This function has been added on a provisional basis (see :pep:`411`
+      for details.)  Use it only for debugging purposes.
+
+
 .. function:: get_coroutine_wrapper()
 
    Returns ``None``, or a wrapper set by :func:`set_coroutine_wrapper`.
@@ -686,6 +698,10 @@ always available.
       This function has been added on a provisional basis (see :pep:`411`
       for details.)  Use it only for debugging purposes.
 
+   .. deprecated:: 3.7
+      The coroutine wrapper functionality has been deprecated, and
+      will be removed in 3.8. See :issue:`32591` for details.
+
 
 .. data:: hash_info
 
@@ -1212,6 +1228,26 @@ always available.
       This function has been added on a provisional basis (see :pep:`411`
       for details.)
 
+.. function:: set_coroutine_origin_tracking_depth(depth)
+
+   Allows enabling or disabling coroutine origin tracking. When
+   enabled, the ``cr_origin`` attribute on coroutine objects will
+   contain a tuple of (filename, line number, function name) tuples
+   describing the traceback where the coroutine object was created,
+   with the most recent call first. When disabled, ``cr_origin`` will
+   be None.
+
+   To enable, pass a *depth* value greater than zero; this sets the
+   number of frames whose information will be captured. To disable,
+   pass set *depth* to zero.
+
+   This setting is thread-specific.
+
+   .. versionadded:: 3.7
+
+   .. note::
+      This function has been added on a provisional basis (see :pep:`411`
+      for details.)  Use it only for debugging purposes.
 
 .. function:: set_coroutine_wrapper(wrapper)
 
@@ -1252,6 +1288,10 @@ always available.
       This function has been added on a provisional basis (see :pep:`411`
       for details.)  Use it only for debugging purposes.
 
+   .. deprecated:: 3.7
+      The coroutine wrapper functionality has been deprecated, and
+      will be removed in 3.8. See :issue:`32591` for details.
+
 .. function:: _enablelegacywindowsfsencoding()
 
    Changes the default filesystem encoding and errors mode to 'mbcs' and
diff --git a/Doc/whatsnew/3.7.rst b/Doc/whatsnew/3.7.rst
index 009df38..54a3f14 100644
--- a/Doc/whatsnew/3.7.rst
+++ b/Doc/whatsnew/3.7.rst
@@ -510,6 +510,9 @@ sys
 
 Added :attr:`sys.flags.dev_mode` flag for the new development mode.
 
+Deprecated :func:`sys.set_coroutine_wrapper` and
+:func:`sys.get_coroutine_wrapper`.
+
 time
 ----
 
diff --git a/Include/ceval.h b/Include/ceval.h
index 70306b8..bce8a0b 100644
--- a/Include/ceval.h
+++ b/Include/ceval.h
@@ -31,6 +31,8 @@ PyAPI_FUNC(PyObject *) PyEval_CallMethod(PyObject *obj,
 #ifndef Py_LIMITED_API
 PyAPI_FUNC(void) PyEval_SetProfile(Py_tracefunc, PyObject *);
 PyAPI_FUNC(void) PyEval_SetTrace(Py_tracefunc, PyObject *);
+PyAPI_FUNC(void) _PyEval_SetCoroutineOriginTrackingDepth(int new_depth);
+PyAPI_FUNC(int) _PyEval_GetCoroutineOriginTrackingDepth(void);
 PyAPI_FUNC(void) _PyEval_SetCoroutineWrapper(PyObject *);
 PyAPI_FUNC(PyObject *) _PyEval_GetCoroutineWrapper(void);
 PyAPI_FUNC(void) _PyEval_SetAsyncGenFirstiter(PyObject *);
diff --git a/Include/genobject.h b/Include/genobject.h
index 87fbe17..16b9833 100644
--- a/Include/genobject.h
+++ b/Include/genobject.h
@@ -51,6 +51,7 @@ PyAPI_FUNC(void) _PyGen_Finalize(PyObject *self);
 #ifndef Py_LIMITED_API
 typedef struct {
     _PyGenObject_HEAD(cr)
+    PyObject *cr_origin;
 } PyCoroObject;
 
 PyAPI_DATA(PyTypeObject) PyCoro_Type;
diff --git a/Include/pystate.h b/Include/pystate.h
index a481528..5a69e14 100644
--- a/Include/pystate.h
+++ b/Include/pystate.h
@@ -262,6 +262,8 @@ typedef struct _ts {
     void (*on_delete)(void *);
     void *on_delete_data;
 
+    int coroutine_origin_tracking_depth;
+
     PyObject *coroutine_wrapper;
     int in_coroutine_wrapper;
 
diff --git a/Include/warnings.h b/Include/warnings.h
index a3f83ff..a675bb5 100644
--- a/Include/warnings.h
+++ b/Include/warnings.h
@@ -56,6 +56,10 @@ PyErr_WarnExplicitFormat(PyObject *category,
 #define PyErr_Warn(category, msg) PyErr_WarnEx(category, msg, 1)
 #endif
 
+#ifndef Py_LIMITED_API
+void _PyErr_WarnUnawaitedCoroutine(PyObject *coro);
+#endif
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/Lib/asyncio/base_events.py b/Lib/asyncio/base_events.py
index 00c84a8..a10e706 100644
--- a/Lib/asyncio/base_events.py
+++ b/Lib/asyncio/base_events.py
@@ -34,6 +34,7 @@ try:
 except ImportError:  # pragma: no cover
     ssl = None
 
+from . import constants
 from . import coroutines
 from . import events
 from . import futures
@@ -224,7 +225,8 @@ class BaseEventLoop(events.AbstractEventLoop):
         self.slow_callback_duration = 0.1
         self._current_handle = None
         self._task_factory = None
-        self._coroutine_wrapper_set = False
+        self._coroutine_origin_tracking_enabled = False
+        self._coroutine_origin_tracking_saved_depth = None
 
         if hasattr(sys, 'get_asyncgen_hooks'):
             # Python >= 3.6
@@ -382,7 +384,7 @@ class BaseEventLoop(events.AbstractEventLoop):
         if events._get_running_loop() is not None:
             raise RuntimeError(
                 'Cannot run the event loop while another loop is running')
-        self._set_coroutine_wrapper(self._debug)
+        self._set_coroutine_origin_tracking(self._debug)
         self._thread_id = threading.get_ident()
         if self._asyncgens is not None:
             old_agen_hooks = sys.get_asyncgen_hooks()
@@ -398,7 +400,7 @@ class BaseEventLoop(events.AbstractEventLoop):
             self._stopping = False
             self._thread_id = None
             events._set_running_loop(None)
-            self._set_coroutine_wrapper(False)
+            self._set_coroutine_origin_tracking(False)
             if self._asyncgens is not None:
                 sys.set_asyncgen_hooks(*old_agen_hooks)
 
@@ -1531,39 +1533,20 @@ class BaseEventLoop(events.AbstractEventLoop):
                 handle._run()
         handle = None  # Needed to break cycles when an exception occurs.
 
-    def _set_coroutine_wrapper(self, enabled):
-        try:
-            set_wrapper = sys.set_coroutine_wrapper
-            get_wrapper = sys.get_coroutine_wrapper
-        except AttributeError:
-            return
-
-        enabled = bool(enabled)
-        if self._coroutine_wrapper_set == enabled:
+    def _set_coroutine_origin_tracking(self, enabled):
+        if bool(enabled) == bool(self._coroutine_origin_tracking_enabled):
             return
 
-        wrapper = coroutines.debug_wrapper
-        current_wrapper = get_wrapper()
-
         if enabled:
-            if current_wrapper not in (None, wrapper):
-                warnings.warn(
-                    f"loop.set_debug(True): cannot set debug coroutine "
-                    f"wrapper; another wrapper is already set "
-                    f"{current_wrapper!r}",
-                    RuntimeWarning)
-            else:
-                set_wrapper(wrapper)
-                self._coroutine_wrapper_set = True
+            self._coroutine_origin_tracking_saved_depth = (
+                sys.get_coroutine_origin_tracking_depth())
+            sys.set_coroutine_origin_tracking_depth(
+                constants.DEBUG_STACK_DEPTH)
         else:
-            if current_wrapper not in (None, wrapper):
-                warnings.warn(
-                    f"loop.set_debug(False): cannot unset debug coroutine "
-                    f"wrapper; another wrapper was set {current_wrapper!r}",
-                    RuntimeWarning)
-            else:
-                set_wrapper(None)
-                self._coroutine_wrapper_set = False
+            sys.set_coroutine_origin_tracking_depth(
+                self._coroutine_origin_tracking_saved_depth)
+
+        self._coroutine_origin_tracking_enabled = enabled
 
     def get_debug(self):
         return self._debug
@@ -1572,4 +1555,4 @@ class BaseEventLoop(events.AbstractEventLoop):
         self._debug = enabled
 
         if self.is_running():
-            self._set_coroutine_wrapper(enabled)
+            self.call_soon_threadsafe(self._set_coroutine_origin_tracking, enabled)
diff --git a/Lib/asyncio/coroutines.py b/Lib/asyncio/coroutines.py
index 9c860a4..5a29100 100644
--- a/Lib/asyncio/coroutines.py
+++ b/Lib/asyncio/coroutines.py
@@ -32,14 +32,6 @@ def _is_debug_mode():
 _DEBUG = _is_debug_mode()
 
 
-def debug_wrapper(gen):
-    # This function is called from 'sys.set_coroutine_wrapper'.
-    # We only wrap here coroutines defined via 'async def' syntax.
-    # Generator-based coroutines are wrapped in @coroutine
-    # decorator.
-    return CoroWrapper(gen, None)
-
-
 class CoroWrapper:
     # Wrapper for coroutine object in _DEBUG mode.
 
@@ -87,39 +79,16 @@ class CoroWrapper:
         return self.gen.gi_code
 
     def __await__(self):
-        cr_await = getattr(self.gen, 'cr_await', None)
-        if cr_await is not None:
-            raise RuntimeError(
-                f"Cannot await on coroutine {self.gen!r} while it's "
-                f"awaiting for {cr_await!r}")
         return self
 
     @property
     def gi_yieldfrom(self):
         return self.gen.gi_yieldfrom
 
-    @property
-    def cr_await(self):
-        return self.gen.cr_await
-
-    @property
-    def cr_running(self):
-        return self.gen.cr_running
-
-    @property
-    def cr_code(self):
-        return self.gen.cr_code
-
-    @property
-    def cr_frame(self):
-        return self.gen.cr_frame
-
     def __del__(self):
         # Be careful accessing self.gen.frame -- self.gen might not exist.
         gen = getattr(self, 'gen', None)
         frame = getattr(gen, 'gi_frame', None)
-        if frame is None:
-            frame = getattr(gen, 'cr_frame', None)
         if frame is not None and frame.f_lasti == -1:
             msg = f'{self!r} was never yielded from'
             tb = getattr(self, '_source_traceback', ())
@@ -141,8 +110,6 @@ def coroutine(func):
     if inspect.iscoroutinefunction(func):
         # In Python 3.5 that's all we need to do for coroutines
         # defined with "async def".
-        # Wrapping in CoroWrapper will happen via
-        # 'sys.set_coroutine_wrapper' function.
         return func
 
     if inspect.isgeneratorfunction(func):
diff --git a/Lib/test/test_asyncio/test_pep492.py b/Lib/test/test_asyncio/test_pep492.py
index 289f7e5..f2d588f 100644
--- a/Lib/test/test_asyncio/test_pep492.py
+++ b/Lib/test/test_asyncio/test_pep492.py
@@ -1,5 +1,6 @@
 """Tests support for new syntax introduced by PEP 492."""
 
+import sys
 import types
 import unittest
 
@@ -148,35 +149,14 @@ class CoroutineTests(BaseTest):
         data = self.loop.run_until_complete(foo())
         self.assertEqual(data, 'spam')
 
-    @mock.patch('asyncio.coroutines.logger')
-    def test_async_def_wrapped(self, m_log):
-        async def foo():
-            pass
+    def test_debug_mode_manages_coroutine_origin_tracking(self):
         async def start():
-            foo_coro = foo()
-            self.assertRegex(
-                repr(foo_coro),
-                r'<CoroWrapper .*\.foo\(\) running at .*pep492.*>')
-
-            with support.check_warnings((r'.*foo.*was never',
-                                         RuntimeWarning)):
-                foo_coro = None
-                support.gc_collect()
-                self.assertTrue(m_log.error.called)
-                message = m_log.error.call_args[0][0]
-                self.assertRegex(message,
-                                 r'CoroWrapper.*foo.*was never')
+            self.assertTrue(sys.get_coroutine_origin_tracking_depth() > 0)
 
+        self.assertEqual(sys.get_coroutine_origin_tracking_depth(), 0)
         self.loop.set_debug(True)
         self.loop.run_until_complete(start())
-
-        async def start():
-            foo_coro = foo()
-            task = asyncio.ensure_future(foo_coro, loop=self.loop)
-            self.assertRegex(repr(task), r'Task.*foo.*running')
-
-        self.loop.run_until_complete(start())
-
+        self.assertEqual(sys.get_coroutine_origin_tracking_depth(), 0)
 
     def test_types_coroutine(self):
         def gen():
@@ -226,9 +206,9 @@ class CoroutineTests(BaseTest):
                 t.cancel()
 
         self.loop.set_debug(True)
-        with self.assertRaisesRegex(
-            RuntimeError,
-            r'Cannot await.*test_double_await.*\bafunc\b.*while.*\bsleep\b'):
+        with self.assertRaises(
+                RuntimeError,
+                msg='coroutine is being awaited already'):
 
             self.loop.run_until_complete(runner())
 
diff --git a/Lib/test/test_coroutines.py b/Lib/test/test_coroutines.py
index d7d38a3..8a531b8 100644
--- a/Lib/test/test_coroutines.py
+++ b/Lib/test/test_coroutines.py
@@ -2,6 +2,7 @@ import contextlib
 import copy
 import inspect
 import pickle
+import re
 import sys
 import types
 import unittest
@@ -1974,9 +1975,11 @@ class SysSetCoroWrapperTest(unittest.TestCase):
             wrapped = gen
             return gen
 
-        self.assertIsNone(sys.get_coroutine_wrapper())
+        with self.assertWarns(DeprecationWarning):
+            self.assertIsNone(sys.get_coroutine_wrapper())
 
-        sys.set_coroutine_wrapper(wrap)
+        with self.assertWarns(DeprecationWarning):
+            sys.set_coroutine_wrapper(wrap)
         self.assertIs(sys.get_coroutine_wrapper(), wrap)
         try:
             f = foo()
@@ -2041,6 +2044,130 @@ class SysSetCoroWrapperTest(unittest.TestCase):
             sys.set_coroutine_wrapper(None)
 
 
+class OriginTrackingTest(unittest.TestCase):
+    def here(self):
+        info = inspect.getframeinfo(inspect.currentframe().f_back)
+        return (info.filename, info.lineno)
+
+    def test_origin_tracking(self):
+        orig_depth = sys.get_coroutine_origin_tracking_depth()
+        try:
+            async def corofn():
+                pass
+
+            sys.set_coroutine_origin_tracking_depth(0)
+            self.assertEqual(sys.get_coroutine_origin_tracking_depth(), 0)
+
+            with contextlib.closing(corofn()) as coro:
+                self.assertIsNone(coro.cr_origin)
+
+            sys.set_coroutine_origin_tracking_depth(1)
+            self.assertEqual(sys.get_coroutine_origin_tracking_depth(), 1)
+
+            fname, lineno = self.here()
+            with contextlib.closing(corofn()) as coro:
+                self.assertEqual(coro.cr_origin,
+                                 ((fname, lineno + 1, "test_origin_tracking"),))
+
+            sys.set_coroutine_origin_tracking_depth(2)
+            self.assertEqual(sys.get_coroutine_origin_tracking_depth(), 2)
+
+            def nested():
+                return (self.here(), corofn())
+            fname, lineno = self.here()
+            ((nested_fname, nested_lineno), coro) = nested()
+            with contextlib.closing(coro):
+                self.assertEqual(coro.cr_origin,
+                                 ((nested_fname, nested_lineno, "nested"),
+                                  (fname, lineno + 1, "test_origin_tracking")))
+
+            # Check we handle running out of frames correctly
+            sys.set_coroutine_origin_tracking_depth(1000)
+            with contextlib.closing(corofn()) as coro:
+                self.assertTrue(2 < len(coro.cr_origin) < 1000)
+
+            # We can't set depth negative
+            with self.assertRaises(ValueError):
+                sys.set_coroutine_origin_tracking_depth(-1)
+            # And trying leaves it unchanged
+            self.assertEqual(sys.get_coroutine_origin_tracking_depth(), 1000)
+
+        finally:
+            sys.set_coroutine_origin_tracking_depth(orig_depth)
+
+    def test_origin_tracking_warning(self):
+        async def corofn():
+            pass
+
+        a1_filename, a1_lineno = self.here()
+        def a1():
+            return corofn()  # comment in a1
+        a1_lineno += 2
+
+        a2_filename, a2_lineno = self.here()
+        def a2():
+            return a1()  # comment in a2
+        a2_lineno += 2
+
+        def check(depth, msg):
+            sys.set_coroutine_origin_tracking_depth(depth)
+            with warnings.catch_warnings(record=True) as wlist:
+                a2()
+                support.gc_collect()
+            # This might be fragile if other warnings somehow get triggered
+            # inside our 'with' block... let's worry about that if/when it
+            # happens.
+            self.assertTrue(len(wlist) == 1)
+            self.assertIs(wlist[0].category, RuntimeWarning)
+            self.assertEqual(msg, str(wlist[0].message))
+
+        orig_depth = sys.get_coroutine_origin_tracking_depth()
+        try:
+            msg = check(0, f"coroutine '{corofn.__qualname__}' was never awaited")
+            check(1, "".join([
+                f"coroutine '{corofn.__qualname__}' was never awaited\n",
+                "Coroutine created at (most recent call last)\n",
+                f'  File "{a1_filename}", line {a1_lineno}, in a1\n',
+                f'    return corofn()  # comment in a1',
+            ]))
+            check(2, "".join([
+                f"coroutine '{corofn.__qualname__}' was never awaited\n",
+                "Coroutine created at (most recent call last)\n",
+                f'  File "{a2_filename}", line {a2_lineno}, in a2\n',
+                f'    return a1()  # comment in a2\n',
+                f'  File "{a1_filename}", line {a1_lineno}, in a1\n',
+                f'    return corofn()  # comment in a1',
+            ]))
+
+        finally:
+            sys.set_coroutine_origin_tracking_depth(orig_depth)
+
+    def test_unawaited_warning_when_module_broken(self):
+        # Make sure we don't blow up too bad if
+        # warnings._warn_unawaited_coroutine is broken somehow (e.g. because
+        # of shutdown problems)
+        async def corofn():
+            pass
+
+        orig_wuc = warnings._warn_unawaited_coroutine
+        try:
+            warnings._warn_unawaited_coroutine = lambda coro: 1/0
+            with support.captured_stderr() as stream:
+                corofn()
+                support.gc_collect()
+            self.assertIn("Exception ignored in", stream.getvalue())
+            self.assertIn("ZeroDivisionError", stream.getvalue())
+            self.assertIn("was never awaited", stream.getvalue())
+
+            del warnings._warn_unawaited_coroutine
+            with support.captured_stderr() as stream:
+                corofn()
+                support.gc_collect()
+            self.assertIn("was never awaited", stream.getvalue())
+
+        finally:
+            warnings._warn_unawaited_coroutine = orig_wuc
+
 @support.cpython_only
 class CAPITest(unittest.TestCase):
 
diff --git a/Lib/warnings.py b/Lib/warnings.py
index 76ad4da..81f9864 100644
--- a/Lib/warnings.py
+++ b/Lib/warnings.py
@@ -488,6 +488,29 @@ class catch_warnings(object):
         self._module._showwarnmsg_impl = self._showwarnmsg_impl
 
 
+# Private utility function called by _PyErr_WarnUnawaitedCoroutine
+def _warn_unawaited_coroutine(coro):
+    msg_lines = [
+        f"coroutine '{coro.__qualname__}' was never awaited\n"
+    ]
+    if coro.cr_origin is not None:
+        import linecache, traceback
+        def extract():
+            for filename, lineno, funcname in reversed(coro.cr_origin):
+                line = linecache.getline(filename, lineno)
+                yield (filename, lineno, funcname, line)
+        msg_lines.append("Coroutine created at (most recent call last)\n")
+        msg_lines += traceback.format_list(list(extract()))
+    msg = "".join(msg_lines).rstrip("\n")
+    # Passing source= here means that if the user happens to have tracemalloc
+    # enabled and tracking where the coroutine was created, the warning will
+    # contain that traceback. This does mean that if they have *both*
+    # coroutine origin tracking *and* tracemalloc enabled, they'll get two
+    # partially-redundant tracebacks. If we wanted to be clever we could
+    # probably detect this case and avoid it, but for now we don't bother.
+    warn(msg, category=RuntimeWarning, stacklevel=2, source=coro)
+
+
 # filters contains a sequence of filter 5-tuples
 # The components of the 5-tuple are:
 # - an action: error, ignore, always, default, module, or once
diff --git a/Misc/ACKS b/Misc/ACKS
index 009b072..900604c 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -1486,6 +1486,7 @@ Christopher Smith
 Eric V. Smith
 Gregory P. Smith
 Mark Smith
+Nathaniel J. Smith
 Roy Smith
 Ryan Smith-Roberts
 Rafal Smotrzyk
diff --git a/Misc/NEWS.d/next/Core and Builtins/2018-01-20-00-50-33.bpo-32591.666kl6.rst b/Misc/NEWS.d/next/Core and Builtins/2018-01-20-00-50-33.bpo-32591.666kl6.rst
new file mode 100644
index 0000000..e3f3d59
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2018-01-20-00-50-33.bpo-32591.666kl6.rst
@@ -0,0 +1,4 @@
+Added built-in support for tracking the origin of coroutine objects; see
+sys.set_coroutine_origin_tracking_depth and CoroutineType.cr_origin. This
+replaces the asyncio debug mode's use of coroutine wrapping for native
+coroutine objects.
diff --git a/Objects/genobject.c b/Objects/genobject.c
index 00a8823..0a34c1f 100644
--- a/Objects/genobject.c
+++ b/Objects/genobject.c
@@ -32,6 +32,8 @@ gen_traverse(PyGenObject *gen, visitproc visit, void *arg)
     Py_VISIT(gen->gi_code);
     Py_VISIT(gen->gi_name);
     Py_VISIT(gen->gi_qualname);
+    /* No need to visit cr_origin, because it's just tuples/str/int, so can't
+       participate in a reference cycle. */
     return exc_state_traverse(&gen->gi_exc_state, visit, arg);
 }
 
@@ -75,9 +77,7 @@ _PyGen_Finalize(PyObject *self)
         ((PyCodeObject *)gen->gi_code)->co_flags & CO_COROUTINE &&
         gen->gi_frame->f_lasti == -1) {
         if (!error_value) {
-            PyErr_WarnFormat(PyExc_RuntimeWarning, 1,
-                             "coroutine '%.50S' was never awaited",
-                             gen->gi_qualname);
+            _PyErr_WarnUnawaitedCoroutine((PyObject *)gen);
         }
     }
     else {
@@ -137,6 +137,9 @@ gen_dealloc(PyGenObject *gen)
         gen->gi_frame->f_gen = NULL;
         Py_CLEAR(gen->gi_frame);
     }
+    if (((PyCodeObject *)gen->gi_code)->co_flags & CO_COROUTINE) {
+        Py_CLEAR(((PyCoroObject *)gen)->cr_origin);
+    }
     Py_CLEAR(gen->gi_code);
     Py_CLEAR(gen->gi_name);
     Py_CLEAR(gen->gi_qualname);
@@ -990,6 +993,7 @@ static PyMemberDef coro_memberlist[] = {
     {"cr_frame",     T_OBJECT, offsetof(PyCoroObject, cr_frame),    READONLY},
     {"cr_running",   T_BOOL,   offsetof(PyCoroObject, cr_running),  READONLY},
     {"cr_code",      T_OBJECT, offsetof(PyCoroObject, cr_code),     READONLY},
+    {"cr_origin",    T_OBJECT, offsetof(PyCoroObject, cr_origin),   READONLY},
     {NULL}      /* Sentinel */
 };
 
@@ -1158,10 +1162,59 @@ PyTypeObject _PyCoroWrapper_Type = {
     0,                                          /* tp_free */
 };
 
+static PyObject *
+compute_cr_origin(int origin_depth)
+{
+    PyFrameObject *frame = PyEval_GetFrame();
+    /* First count how many frames we have */
+    int frame_count = 0;
+    for (; frame && frame_count < origin_depth; ++frame_count) {
+        frame = frame->f_back;
+    }
+
+    /* Now collect them */
+    PyObject *cr_origin = PyTuple_New(frame_count);
+    frame = PyEval_GetFrame();
+    for (int i = 0; i < frame_count; ++i) {
+        PyObject *frameinfo = Py_BuildValue(
+            "OiO",
+            frame->f_code->co_filename,
+            PyFrame_GetLineNumber(frame),
+            frame->f_code->co_name);
+        if (!frameinfo) {
+            Py_DECREF(cr_origin);
+            return NULL;
+        }
+        PyTuple_SET_ITEM(cr_origin, i, frameinfo);
+        frame = frame->f_back;
+    }
+
+    return cr_origin;
+}
+
 PyObject *
 PyCoro_New(PyFrameObject *f, PyObject *name, PyObject *qualname)
 {
-    return gen_new_with_qualname(&PyCoro_Type, f, name, qualname);
+    PyObject *coro = gen_new_with_qualname(&PyCoro_Type, f, name, qualname);
+    if (!coro) {
+        return NULL;
+    }
+
+    PyThreadState *tstate = PyThreadState_GET();
+    int origin_depth = tstate->coroutine_origin_tracking_depth;
+
+    if (origin_depth == 0) {
+        ((PyCoroObject *)coro)->cr_origin = NULL;
+    } else {
+        PyObject *cr_origin = compute_cr_origin(origin_depth);
+        if (!cr_origin) {
+            Py_DECREF(coro);
+            return NULL;
+        }
+        ((PyCoroObject *)coro)->cr_origin = cr_origin;
+    }
+
+    return coro;
 }
 
 
diff --git a/Python/_warnings.c b/Python/_warnings.c
index c286364..c3417cc 100644
--- a/Python/_warnings.c
+++ b/Python/_warnings.c
@@ -1153,6 +1153,53 @@ exit:
     return ret;
 }
 
+void
+_PyErr_WarnUnawaitedCoroutine(PyObject *coro)
+{
+    /* First, we attempt to funnel the warning through
+       warnings._warn_unawaited_coroutine.
+
+       This could raise an exception, due to:
+       - a bug
+       - some kind of shutdown-related brokenness
+       - succeeding, but with an "error" warning filter installed, so the
+         warning is converted into a RuntimeWarning exception
+
+       In the first two cases, we want to print the error (so we know what it
+       is!), and then print a warning directly as a fallback. In the last
+       case, we want to print the error (since it's the warning!), but *not*
+       do a fallback. And after we print the error we can't check for what
+       type of error it was (because PyErr_WriteUnraisable clears it), so we
+       need a flag to keep track.
+
+       Since this is called from __del__ context, it's careful to never raise
+       an exception.
+    */
+    _Py_IDENTIFIER(_warn_unawaited_coroutine);
+    int warned = 0;
+    PyObject *fn = get_warnings_attr(&PyId__warn_unawaited_coroutine, 1);
+    if (fn) {
+        PyObject *res = PyObject_CallFunctionObjArgs(fn, coro, NULL);
+        Py_DECREF(fn);
+        if (res || PyErr_ExceptionMatches(PyExc_RuntimeWarning)) {
+            warned = 1;
+        }
+        Py_XDECREF(res);
+    }
+
+    if (PyErr_Occurred()) {
+        PyErr_WriteUnraisable(coro);
+    }
+    if (!warned) {
+        PyErr_WarnFormat(PyExc_RuntimeWarning, 1,
+                         "coroutine '%.50S' was never awaited",
+                         ((PyCoroObject *)coro)->cr_qualname);
+        /* Maybe *that* got converted into an exception */
+        if (PyErr_Occurred()) {
+            PyErr_WriteUnraisable(coro);
+        }
+    }
+}
 
 PyDoc_STRVAR(warn_explicit_doc,
 "Low-level inferface to warnings functionality.");
diff --git a/Python/ceval.c b/Python/ceval.c
index 9276755..2b7c0c8 100644
--- a/Python/ceval.c
+++ b/Python/ceval.c
@@ -4388,6 +4388,21 @@ PyEval_SetTrace(Py_tracefunc func, PyObject *arg)
 }
 
 void
+_PyEval_SetCoroutineOriginTrackingDepth(int new_depth)
+{
+    assert(new_depth >= 0);
+    PyThreadState *tstate = PyThreadState_GET();
+    tstate->coroutine_origin_tracking_depth = new_depth;
+}
+
+int
+_PyEval_GetCoroutineOriginTrackingDepth(void)
+{
+    PyThreadState *tstate = PyThreadState_GET();
+    return tstate->coroutine_origin_tracking_depth;
+}
+
+void
 _PyEval_SetCoroutineWrapper(PyObject *wrapper)
 {
     PyThreadState *tstate = PyThreadState_GET();
diff --git a/Python/clinic/sysmodule.c.h b/Python/clinic/sysmodule.c.h
new file mode 100644
index 0000000..3e14805
--- /dev/null
+++ b/Python/clinic/sysmodule.c.h
@@ -0,0 +1,66 @@
+/*[clinic input]
+preserve
+[clinic start generated code]*/
+
+PyDoc_STRVAR(sys_set_coroutine_origin_tracking_depth__doc__,
+"set_coroutine_origin_tracking_depth($module, /, depth)\n"
+"--\n"
+"\n"
+"Enable or disable origin tracking for coroutine objects in this thread.\n"
+"\n"
+"Coroutine objects will track \'depth\' frames of traceback information about\n"
+"where they came from, available in their cr_origin attribute. Set depth of 0\n"
+"to disable.");
+
+#define SYS_SET_COROUTINE_ORIGIN_TRACKING_DEPTH_METHODDEF    \
+    {"set_coroutine_origin_tracking_depth", (PyCFunction)sys_set_coroutine_origin_tracking_depth, METH_FASTCALL|METH_KEYWORDS, sys_set_coroutine_origin_tracking_depth__doc__},
+
+static PyObject *
+sys_set_coroutine_origin_tracking_depth_impl(PyObject *module, int depth);
+
+static PyObject *
+sys_set_coroutine_origin_tracking_depth(PyObject *module, PyObject *const *args, Py_ssize_t nargs, PyObject *kwnames)
+{
+    PyObject *return_value = NULL;
+    static const char * const _keywords[] = {"depth", NULL};
+    static _PyArg_Parser _parser = {"i:set_coroutine_origin_tracking_depth", _keywords, 0};
+    int depth;
+
+    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser,
+        &depth)) {
+        goto exit;
+    }
+    return_value = sys_set_coroutine_origin_tracking_depth_impl(module, depth);
+
+exit:
+    return return_value;
+}
+
+PyDoc_STRVAR(sys_get_coroutine_origin_tracking_depth__doc__,
+"get_coroutine_origin_tracking_depth($module, /)\n"
+"--\n"
+"\n"
+"Check status of origin tracking for coroutine objects in this thread.");
+
+#define SYS_GET_COROUTINE_ORIGIN_TRACKING_DEPTH_METHODDEF    \
+    {"get_coroutine_origin_tracking_depth", (PyCFunction)sys_get_coroutine_origin_tracking_depth, METH_NOARGS, sys_get_coroutine_origin_tracking_depth__doc__},
+
+static int
+sys_get_coroutine_origin_tracking_depth_impl(PyObject *module);
+
+static PyObject *
+sys_get_coroutine_origin_tracking_depth(PyObject *module, PyObject *Py_UNUSED(ignored))
+{
+    PyObject *return_value = NULL;
+    int _return_value;
+
+    _return_value = sys_get_coroutine_origin_tracking_depth_impl(module);
+    if ((_return_value == -1) && PyErr_Occurred()) {
+        goto exit;
+    }
+    return_value = PyLong_FromLong((long)_return_value);
+
+exit:
+    return return_value;
+}
+/*[clinic end generated code: output=4a3ac42b97d710ff input=a9049054013a1b77]*/
diff --git a/Python/pystate.c b/Python/pystate.c
index 028292e..9c25a26 100644
--- a/Python/pystate.c
+++ b/Python/pystate.c
@@ -305,6 +305,8 @@ new_threadstate(PyInterpreterState *interp, int init)
         tstate->on_delete = NULL;
         tstate->on_delete_data = NULL;
 
+        tstate->coroutine_origin_tracking_depth = 0;
+
         tstate->coroutine_wrapper = NULL;
         tstate->in_coroutine_wrapper = 0;
 
diff --git a/Python/sysmodule.c b/Python/sysmodule.c
index c054243..873657f 100644
--- a/Python/sysmodule.c
+++ b/Python/sysmodule.c
@@ -34,6 +34,13 @@ extern void *PyWin_DLLhModule;
 extern const char *PyWin_DLLVersionString;
 #endif
 
+/*[clinic input]
+module sys
+[clinic start generated code]*/
+/*[clinic end generated code: output=da39a3ee5e6b4b0d input=3726b388feee8cea]*/
+
+#include "clinic/sysmodule.c.h"
+
 _Py_IDENTIFIER(_);
 _Py_IDENTIFIER(__sizeof__);
 _Py_IDENTIFIER(_xoptions);
@@ -710,9 +717,51 @@ sys_setrecursionlimit(PyObject *self, PyObject *args)
     Py_RETURN_NONE;
 }
 
+/*[clinic input]
+sys.set_coroutine_origin_tracking_depth
+
+  depth: int
+
+Enable or disable origin tracking for coroutine objects in this thread.
+
+Coroutine objects will track 'depth' frames of traceback information about
+where they came from, available in their cr_origin attribute. Set depth of 0
+to disable.
+[clinic start generated code]*/
+
+static PyObject *
+sys_set_coroutine_origin_tracking_depth_impl(PyObject *module, int depth)
+/*[clinic end generated code: output=0a2123c1cc6759c5 input=9083112cccc1bdcb]*/
+{
+    if (depth < 0) {
+        PyErr_SetString(PyExc_ValueError, "depth must be >= 0");
+        return NULL;
+    }
+    _PyEval_SetCoroutineOriginTrackingDepth(depth);
+    Py_RETURN_NONE;
+}
+
+/*[clinic input]
+sys.get_coroutine_origin_tracking_depth -> int
+
+Check status of origin tracking for coroutine objects in this thread.
+[clinic start generated code]*/
+
+static int
+sys_get_coroutine_origin_tracking_depth_impl(PyObject *module)
+/*[clinic end generated code: output=3699f7be95a3afb8 input=335266a71205b61a]*/
+{
+    return _PyEval_GetCoroutineOriginTrackingDepth();
+}
+
 static PyObject *
 sys_set_coroutine_wrapper(PyObject *self, PyObject *wrapper)
 {
+    if (PyErr_WarnEx(PyExc_DeprecationWarning,
+                     "set_coroutine_wrapper is deprecated", 1) < 0) {
+        return NULL;
+    }
+
     if (wrapper != Py_None) {
         if (!PyCallable_Check(wrapper)) {
             PyErr_Format(PyExc_TypeError,
@@ -737,6 +786,10 @@ Set a wrapper for coroutine objects."
 static PyObject *
 sys_get_coroutine_wrapper(PyObject *self, PyObject *args)
 {
+    if (PyErr_WarnEx(PyExc_DeprecationWarning,
+                     "get_coroutine_wrapper is deprecated", 1) < 0) {
+        return NULL;
+    }
     PyObject *wrapper = _PyEval_GetCoroutineWrapper();
     if (wrapper == NULL) {
         wrapper = Py_None;
@@ -1512,6 +1565,8 @@ static PyMethodDef sys_methods[] = {
     {"call_tracing", sys_call_tracing, METH_VARARGS, call_tracing_doc},
     {"_debugmallocstats", sys_debugmallocstats, METH_NOARGS,
      debugmallocstats_doc},
+    SYS_SET_COROUTINE_ORIGIN_TRACKING_DEPTH_METHODDEF
+    SYS_GET_COROUTINE_ORIGIN_TRACKING_DEPTH_METHODDEF
     {"set_coroutine_wrapper", sys_set_coroutine_wrapper, METH_O,
      set_coroutine_wrapper_doc},
     {"get_coroutine_wrapper", sys_get_coroutine_wrapper, METH_NOARGS,