asyncio: sync with Tulip

- Sort imports
- Simplify/optimize iscoroutine(). Inline inspect.isgenerator(obj): replace it
  with isinstance(obj, types.GeneratorType)
- CoroWrapper: check at runtime if Python has the yield-from bug #21209.  If
  Python has the bug, check if CoroWrapper.send() was called by yield-from to
  decide if parameters must be unpacked or not.
- Fix "Task was destroyed but it is pending!" warning in
  test_task_source_traceback()

Lib/asyncio/base_events.py

@@ -19,11 +19,11 @@ import concurrent.futures
 import heapq
 import inspect
 import logging
+import os
 import socket
 import subprocess
-import traceback
 import time
-import os
+import traceback
 import sys
 
 from . import coroutines

Lib/asyncio/coroutines.py

@@ -3,14 +3,20 @@ __all__ = ['coroutine',
 
 import functools
 import inspect
+import opcode
 import os
 import sys
 import traceback
+import types
 
 from . import events
 from . import futures
 from .log import logger
 
+
+# Opcode of "yield from" instruction
+_YIELD_FROM = opcode.opmap['YIELD_FROM']
+
 # If you set _DEBUG to true, @coroutine will wrap the resulting
 # generator objects in a CoroWrapper instance (defined below).  That
 # instance will log a message when the generator is never iterated
@@ -25,6 +31,31 @@ _DEBUG = (not sys.flags.ignore_environment
 
 _PY35 = (sys.version_info >= (3, 5))
 
+
+# Check for CPython issue #21209
+def has_yield_from_bug():
+    class MyGen:
+        def __init__(self):
+            self.send_args = None
+        def __iter__(self):
+            return self
+        def __next__(self):
+            return 42
+        def send(self, *what):
+            self.send_args = what
+            return None
+    def yield_from_gen(gen):
+        yield from gen
+    value = (1, 2, 3)
+    gen = MyGen()
+    coro = yield_from_gen(gen)
+    next(coro)
+    coro.send(value)
+    return gen.send_args != (value,)
+_YIELD_FROM_BUG = has_yield_from_bug()
+del has_yield_from_bug
+
+
 class CoroWrapper:
     # Wrapper for coroutine in _DEBUG mode.
 
@@ -40,13 +71,21 @@ class CoroWrapper:
     def __next__(self):
         return next(self.gen)
 
+    if _YIELD_FROM_BUG:
+        # For for CPython issue #21209: using "yield from" and a custom
+        # generator, generator.send(tuple) unpacks the tuple instead of passing
+        # the tuple unchanged. Check if the caller is a generator using "yield
+        # from" to decide if the parameter should be unpacked or not.
         def send(self, *value):
-        # We use `*value` because of a bug in CPythons prior
-        # to 3.4.1. See issue #21209 and test_yield_from_corowrapper
-        # for details.  This workaround should be removed in 3.5.0.
-        if len(value) == 1:
+            frame = sys._getframe()
+            caller = frame.f_back
+            assert caller.f_lasti >= 0
+            if caller.f_code.co_code[caller.f_lasti] != _YIELD_FROM:
                 value = value[0]
             return self.gen.send(value)
+    else:
+        def send(self, value):
+            return self.gen.send(value)
 
     def throw(self, exc):
         return self.gen.throw(exc)
@@ -119,9 +158,11 @@ def iscoroutinefunction(func):
     return getattr(func, '_is_coroutine', False)
 
 
+_COROUTINE_TYPES = (CoroWrapper, types.GeneratorType)
+
 def iscoroutine(obj):
     """Return True if obj is a coroutine object."""
-    return isinstance(obj, CoroWrapper) or inspect.isgenerator(obj)
+    return isinstance(obj,  _COROUTINE_TYPES)
 
 
 def _format_coroutine(coro):

Lib/test/test_asyncio/test_tasks.py

@@ -1621,6 +1621,7 @@ class TaskTests(test_utils.TestCase):
                          (__file__,
                           lineno,
                           'test_task_source_traceback'))
+        self.loop.run_until_complete(task)
 
 
 class GatherTestsBase: