follow PEP492 change in Py3.5.2 that makes __aiter__() a simple function...

follow PEP492 change in Py3.5.2 that makes __aiter__() a simple function instead of an async function
See https://bugs.python.org/issue27243

Cython/Compiler/ExprNodes.py

@@ -9237,6 +9237,13 @@ class AwaitExprNode(YieldFromExprNode):
         return "__Pyx_Coroutine_Yield_From"
 
 
+class AIterAwaitExprNode(AwaitExprNode):
+    # 'await' expression node used in async-for loops to support the pre-Py3.5.2 'aiter' protocol
+    def yield_from_func(self, code):
+        code.globalstate.use_utility_code(UtilityCode.load_cached("CoroutineAIterYieldFrom", "Coroutine.c"))
+        return "__Pyx_Coroutine_AIter_Yield_From"
+
+
 class AwaitIterNextExprNode(AwaitExprNode):
     # 'await' expression node as part of 'async for' iteration
     #

Cython/Compiler/Nodes.py

@@ -6144,7 +6144,7 @@ class _ForInStatNode(LoopNode, StatNode):
     #  Base class of 'for-in' statements.
     #
     #  target        ExprNode
-    #  iterator      IteratorNode | AwaitExprNode(AsyncIteratorNode)
+    #  iterator      IteratorNode | AIterAwaitExprNode(AsyncIteratorNode)
     #  body          StatNode
     #  else_clause   StatNode
     #  item          NextNode | AwaitExprNode(AsyncNextNode)
@@ -6250,7 +6250,7 @@ class ForInStatNode(_ForInStatNode):
 class AsyncForStatNode(_ForInStatNode):
     #  'async for' statement
     #
-    #  iterator      AwaitExprNode(AsyncIteratorNode)
+    #  iterator      AIterAwaitExprNode(AsyncIteratorNode)
     #  item          AwaitIterNextExprNode(AsyncIteratorNode)
 
     is_async = True
@@ -6259,7 +6259,7 @@ class AsyncForStatNode(_ForInStatNode):
         assert 'item' not in kw
         from . import ExprNodes
         # AwaitExprNodes must appear before running MarkClosureVisitor
-        kw['iterator'] = ExprNodes.AwaitExprNode(iterator.pos, arg=iterator)
+        kw['iterator'] = ExprNodes.AIterAwaitExprNode(iterator.pos, arg=iterator)
         kw['item'] = ExprNodes.AwaitIterNextExprNode(iterator.pos, arg=None)
         _ForInStatNode.__init__(self, pos, **kw)
 

Cython/Utility/Coroutine.c

@@ -45,15 +45,40 @@ static CYTHON_INLINE PyObject* __Pyx_Generator_Yield_From(__pyx_CoroutineObject
 
 //////////////////// CoroutineYieldFrom.proto ////////////////////
 
-static CYTHON_INLINE PyObject* __Pyx_Coroutine_Yield_From(__pyx_CoroutineObject *gen, PyObject *source);
+#define __Pyx_Coroutine_Yield_From(gen, source) __Pyx__Coroutine_Yield_From(gen, source, 0)
+static CYTHON_INLINE PyObject* __Pyx__Coroutine_Yield_From(__pyx_CoroutineObject *gen, PyObject *source, int warn);
 
 //////////////////// CoroutineYieldFrom ////////////////////
 //@requires: Coroutine
 //@requires: GetAwaitIter
 
-static CYTHON_INLINE PyObject* __Pyx_Coroutine_Yield_From(__pyx_CoroutineObject *gen, PyObject *source) {
+static int __Pyx_WarnAIterDeprecation(PyObject *aiter) {
+    int result;
+#if PY_MAJOR_VERSION >= 3
+    result = PyErr_WarnFormat(
+        PyExc_PendingDeprecationWarning, 1,
+        "'%.100s' implements legacy __aiter__ protocol; "
+        "__aiter__ should return an asynchronous "
+        "iterator, not awaitable",
+        Py_TYPE(aiter)->tp_name);
+#else
+    result = PyErr_WarnEx(
+        PyExc_PendingDeprecationWarning,
+        "object implements legacy __aiter__ protocol; "
+        "__aiter__ should return an asynchronous "
+        "iterator, not awaitable",
+        1);
+#endif
+    return result != 0;
+}
+
+static CYTHON_INLINE PyObject* __Pyx__Coroutine_Yield_From(__pyx_CoroutineObject *gen, PyObject *source, int warn) {
     PyObject *retval;
     if (__Pyx_Coroutine_CheckExact(source)) {
+        if (warn && unlikely(__Pyx_WarnAIterDeprecation(source))) {
+            /* Warning was converted to an error. */
+            return NULL;
+        }
         retval = __Pyx_Generator_Next(source);
         if (retval) {
             Py_INCREF(source);
@@ -64,6 +89,11 @@ static CYTHON_INLINE PyObject* __Pyx_Coroutine_Yield_From(__pyx_CoroutineObject
         PyObject *source_gen = __Pyx__Coroutine_GetAwaitableIter(source);
         if (unlikely(!source_gen))
             return NULL;
+        if (warn && unlikely(__Pyx_WarnAIterDeprecation(source))) {
+            /* Warning was converted to an error. */
+            Py_DECREF(source_gen);
+            return NULL;
+        }
         // source_gen is now the iterator, make the first next() call
         if (__Pyx_Coroutine_CheckExact(source_gen)) {
             retval = __Pyx_Generator_Next(source_gen);
@@ -80,6 +110,53 @@ static CYTHON_INLINE PyObject* __Pyx_Coroutine_Yield_From(__pyx_CoroutineObject
 }
 
 
+//////////////////// CoroutineAIterYieldFrom.proto ////////////////////
+
+static CYTHON_INLINE PyObject* __Pyx_Coroutine_AIter_Yield_From(__pyx_CoroutineObject *gen, PyObject *source);
+
+//////////////////// CoroutineAIterYieldFrom ////////////////////
+//@requires: CoroutineYieldFrom
+
+static CYTHON_INLINE PyObject* __Pyx_Coroutine_AIter_Yield_From(__pyx_CoroutineObject *gen, PyObject *source) {
+#if PY_MAJOR_VERSION >= 3
+    __Pyx_PyAsyncMethodsStruct* am = __Pyx_PyType_AsAsync(source);
+    if (likely(am && am->am_anext)) {
+        // Starting with CPython 3.5.2, __aiter__ should return
+        // asynchronous iterators directly (not awaitables that
+        // resolve to asynchronous iterators.)
+        //
+        // Therefore, we check if the object that was returned
+        // from __aiter__ has an __anext__ method.  If it does,
+        // we return it directly as StopIteration result,
+        // which avoids yielding.
+        //
+        // See http://bugs.python.org/issue27243 for more
+        // details.
+        PyErr_SetObject(PyExc_StopIteration, source);
+        return NULL;
+    }
+#endif
+#if PY_VERSION_HEX < 0x030500B2
+    if (!__Pyx_PyType_AsAsync(source)) {
+        #ifdef __Pyx_Coroutine_USED
+        if (!__Pyx_Coroutine_CheckExact(source))  // quickly rule out a likely case
+        #endif
+        {
+            // same as above in slow
+            PyObject *method = __Pyx_PyObject_GetAttrStr(source, PYIDENT("__anext__"));
+            if (method) {
+                Py_DECREF(method);
+                PyErr_SetObject(PyExc_StopIteration, source);
+                return NULL;
+            }
+            PyErr_Clear();
+        }
+    }
+#endif
+    return __Pyx__Coroutine_Yield_From(gen, source, 1);
+}
+
+
 //////////////////// GetAwaitIter.proto ////////////////////
 
 static CYTHON_INLINE PyObject *__Pyx_Coroutine_GetAwaitableIter(PyObject *o); /*proto*/
@@ -196,7 +273,7 @@ static CYTHON_INLINE PyObject *__Pyx_Coroutine_GetAsyncIter(PyObject *obj) {
             return NULL;
     }
 #else
-    // avoid 'unused function' warning
+    // avoid C warning about 'unused function'
     if (0) (void) __Pyx_PyObject_CallMethod0(obj, PYIDENT("__aiter__"));
 #endif
 

tests/run/test_coroutines_pep492.pyx

@@ -5,7 +5,9 @@
 import re
 import gc
 import sys
+import copy
 #import types
+import pickle
 import os.path
 #import inspect
 import unittest
@@ -128,6 +130,17 @@ def silence_coro_gc():
         gc.collect()
 
 
+def min_py27(method):
+    return None if sys.version_info < (2, 7) else method
+
+
+def ignore_py26(manager):
+    @contextlib.contextmanager
+    def dummy():
+        yield
+    return dummy() if sys.version_info < (2, 7) else manager
+
+
 class AsyncBadSyntaxTest(unittest.TestCase):
 
     @contextlib.contextmanager
@@ -1238,6 +1251,7 @@ class CoroutineTest(unittest.TestCase):
 
         buffer = []
         async def test1():
+            with ignore_py26(self.assertWarnsRegex(PendingDeprecationWarning, "legacy")):
                 async for i1, i2 in AsyncIter():
                     buffer.append(i1 + i2)
 
@@ -1251,6 +1265,7 @@ class CoroutineTest(unittest.TestCase):
         buffer = []
         async def test2():
             nonlocal buffer
+            with ignore_py26(self.assertWarnsRegex(PendingDeprecationWarning, "legacy")):
                 async for i in AsyncIter():
                     buffer.append(i[0])
                     if i[0] == 20:
@@ -1269,6 +1284,7 @@ class CoroutineTest(unittest.TestCase):
         buffer = []
         async def test3():
             nonlocal buffer
+            with ignore_py26(self.assertWarnsRegex(PendingDeprecationWarning, "legacy")):
                 async for i in AsyncIter():
                     if i[0] > 20:
                         continue
@@ -1321,7 +1337,7 @@ class CoroutineTest(unittest.TestCase):
 
     def test_for_4(self):
         class I(object):
-            async def __aiter__(self):
+            def __aiter__(self):
                 return self
 
             def __anext__(self):
@@ -1351,6 +1367,7 @@ class CoroutineTest(unittest.TestCase):
                 return 123
 
         async def foo():
+            with self.assertWarnsRegex(PendingDeprecationWarning, "legacy"):
                 async for i in I():
                     print('never going to happen')
 
@@ -1376,7 +1393,7 @@ class CoroutineTest(unittest.TestCase):
             def __init__(self):
                 self.i = 0
 
-            async def __aiter__(self):
+            def __aiter__(self):
                 return self
 
             async def __anext__(self):
@@ -1453,6 +1470,21 @@ class CoroutineTest(unittest.TestCase):
         class AI(object):
             async def __aiter__(self):
                 1/0
+        async def foo():
+            nonlocal CNT
+            with self.assertWarnsRegex(PendingDeprecationWarning, "legacy"):
+                async for i in AI():
+                    CNT += 1
+            CNT += 10
+        with self.assertRaises(ZeroDivisionError):
+            run_async(foo())
+        self.assertEqual(CNT, 0)
+
+    def test_for_8(self):
+        CNT = 0
+        class AI:
+            def __aiter__(self):
+                1/0
         async def foo():
             nonlocal CNT
             async for i in AI():
@@ -1460,8 +1492,74 @@ class CoroutineTest(unittest.TestCase):
             CNT += 10
         with self.assertRaises(ZeroDivisionError):
             run_async(foo())
+            with warnings.catch_warnings():
+                warnings.simplefilter("error")
+                # Test that if __aiter__ raises an exception it propagates
+                # without any kind of warning.
+                run_async(foo())
         self.assertEqual(CNT, 0)
 
+    @min_py27
+    def test_for_9(self):
+        # Test that PendingDeprecationWarning can safely be converted into
+        # an exception (__aiter__ should not have a chance to raise
+        # a ZeroDivisionError.)
+        class AI:
+            async def __aiter__(self):
+                1/0
+        async def foo():
+            async for i in AI():
+                pass
+
+        with self.assertRaises(PendingDeprecationWarning):
+            with warnings.catch_warnings():
+                warnings.simplefilter("error")
+                run_async(foo())
+
+    @min_py27
+    def test_for_10(self):
+        # Test that PendingDeprecationWarning can safely be converted into
+        # an exception.
+        class AI:
+            async def __aiter__(self):
+                pass
+        async def foo():
+            async for i in AI():
+                pass
+
+        with self.assertRaises(PendingDeprecationWarning):
+            with warnings.catch_warnings():
+                warnings.simplefilter("error")
+                run_async(foo())
+
+    def test_copy(self):
+        async def func(): pass
+        coro = func()
+        with self.assertRaises(TypeError):
+            copy.copy(coro)
+
+        aw = coro.__await__()
+        try:
+            with self.assertRaises(TypeError):
+                copy.copy(aw)
+        finally:
+            aw.close()
+
+    def test_pickle(self):
+        async def func(): pass
+        coro = func()
+        for proto in range(pickle.HIGHEST_PROTOCOL + 1):
+            with self.assertRaises((TypeError, pickle.PicklingError)):
+                pickle.dumps(coro, proto)
+
+        aw = coro.__await__()
+        try:
+            for proto in range(pickle.HIGHEST_PROTOCOL + 1):
+                with self.assertRaises((TypeError, pickle.PicklingError)):
+                    pickle.dumps(aw, proto)
+        finally:
+            aw.close()
+
 
 class CoroAsyncIOCompatTest(unittest.TestCase):