Work around error that "__reduce_cython__ cannot be found" when re-importing...

Work around error that "__reduce_cython__ cannot be found" when re-importing an extension module that was already initialised before.
Backport to 0.29.x.
Closes #3545.

Cython/Utility/ExtensionTypes.c

@@ -132,6 +132,7 @@ static void __Pyx_call_next_tp_clear(PyObject* obj, inquiry current_tp_clear) {
 static int __Pyx_setup_reduce(PyObject* type_obj);
 
 /////////////// SetupReduce ///////////////
+//@requires: ObjectHandling.c::PyObjectGetAttrStrNoError
 //@requires: ObjectHandling.c::PyObjectGetAttrStr
 //@substitute: naming
 
@@ -188,16 +189,28 @@ static int __Pyx_setup_reduce(PyObject* type_obj) {
         reduce = __Pyx_PyObject_GetAttrStr(type_obj, PYIDENT("__reduce__")); if (unlikely(!reduce)) goto __PYX_BAD;
 
         if (reduce == object_reduce || __Pyx_setup_reduce_is_named(reduce, PYIDENT("__reduce_cython__"))) {
-            reduce_cython = __Pyx_PyObject_GetAttrStr(type_obj, PYIDENT("__reduce_cython__")); if (unlikely(!reduce_cython)) goto __PYX_BAD;
+            reduce_cython = __Pyx_PyObject_GetAttrStrNoError(type_obj, PYIDENT("__reduce_cython__"));
+            if (likely(reduce_cython)) {
                 ret = PyDict_SetItem(((PyTypeObject*)type_obj)->tp_dict, PYIDENT("__reduce__"), reduce_cython); if (unlikely(ret < 0)) goto __PYX_BAD;
                 ret = PyDict_DelItem(((PyTypeObject*)type_obj)->tp_dict, PYIDENT("__reduce_cython__")); if (unlikely(ret < 0)) goto __PYX_BAD;
+            } else if (reduce == object_reduce || PyErr_Occurred()) {
+                // Ignore if we're done, i.e. if 'reduce' already has the right name and the original is gone.
+                // Otherwise: error.
+                goto __PYX_BAD;
+            }
 
             setstate = __Pyx_PyObject_GetAttrStr(type_obj, PYIDENT("__setstate__"));
             if (!setstate) PyErr_Clear();
             if (!setstate || __Pyx_setup_reduce_is_named(setstate, PYIDENT("__setstate_cython__"))) {
-                setstate_cython = __Pyx_PyObject_GetAttrStr(type_obj, PYIDENT("__setstate_cython__")); if (unlikely(!setstate_cython)) goto __PYX_BAD;
+                setstate_cython = __Pyx_PyObject_GetAttrStrNoError(type_obj, PYIDENT("__setstate_cython__"));
+                if (likely(setstate_cython)) {
                     ret = PyDict_SetItem(((PyTypeObject*)type_obj)->tp_dict, PYIDENT("__setstate__"), setstate_cython); if (unlikely(ret < 0)) goto __PYX_BAD;
                     ret = PyDict_DelItem(((PyTypeObject*)type_obj)->tp_dict, PYIDENT("__setstate_cython__")); if (unlikely(ret < 0)) goto __PYX_BAD;
+                } else if (!setstate || PyErr_Occurred()) {
+                    // Ignore if we're done, i.e. if 'setstate' already has the right name and the original is gone.
+                    // Otherwise: error.
+                    goto __PYX_BAD;
+                }
             }
             PyType_Modified((PyTypeObject*)type_obj);
         }

Cython/Utility/ObjectHandling.c

@@ -1361,6 +1361,41 @@ static PyObject* __Pyx_PyObject_GenericGetAttr(PyObject* obj, PyObject* attr_nam
 #endif
 
 
+/////////////// PyObjectGetAttrStrNoError.proto ///////////////
+
+static CYTHON_INLINE PyObject* __Pyx_PyObject_GetAttrStrNoError(PyObject* obj, PyObject* attr_name);/*proto*/
+
+/////////////// PyObjectGetAttrStrNoError ///////////////
+//@requires: PyObjectGetAttrStr
+//@requires: Exceptions.c::PyThreadStateGet
+//@requires: Exceptions.c::PyErrFetchRestore
+//@requires: Exceptions.c::PyErrExceptionMatches
+
+static void __Pyx_PyObject_GetAttrStr_ClearAttributeError(void) {
+    __Pyx_PyThreadState_declare
+    __Pyx_PyThreadState_assign
+    if (likely(__Pyx_PyErr_ExceptionMatches(PyExc_AttributeError)))
+        __Pyx_PyErr_Clear();
+}
+
+static CYTHON_INLINE PyObject* __Pyx_PyObject_GetAttrStrNoError(PyObject* obj, PyObject* attr_name) {
+    PyObject *result;
+#if CYTHON_COMPILING_IN_CPYTHON && CYTHON_USE_TYPE_SLOTS && PY_VERSION_HEX >= 0x030700B1
+    // _PyObject_GenericGetAttrWithDict() in CPython 3.7+ can avoid raising the AttributeError.
+    // See https://bugs.python.org/issue32544
+    PyTypeObject* tp = Py_TYPE(obj);
+    if (likely(tp->tp_getattro == PyObject_GenericGetAttr)) {
+        return _PyObject_GenericGetAttrWithDict(obj, attr_name, NULL, 1);
+    }
+#endif
+    result = __Pyx_PyObject_GetAttrStr(obj, attr_name);
+    if (unlikely(!result)) {
+        __Pyx_PyObject_GetAttrStr_ClearAttributeError();
+    }
+    return result;
+}
+
+
 /////////////// PyObjectGetAttrStr.proto ///////////////
 
 #if CYTHON_USE_TYPE_SLOTS

runtests.py

@@ -424,6 +424,7 @@ VER_DEP_MODULES = {
     # to be unsafe...
     (2,999): (operator.lt, lambda x: x in ['run.special_methods_T561_py3',
                                            'run.test_raisefrom',
+                                           'run.reimport_failure',  # reimports don't do anything in Py2
                                            ]),
     (3,): (operator.ge, lambda x: x in ['run.non_future_division',
                                         'compile.extsetslice',

tests/pypy_bugs.txt

@@ -11,6 +11,8 @@ sequential_parallel
 yield_from_pep380
 memoryview_inplace_division
 
+run.reimport_failure
+
 # gc issue?
 memoryview_in_subclasses
 external_ref_reassignment

tests/run/reimport_failure.srctree

+# mode: run
+# tag: pep489
+
+"""
+PYTHON setup.py build_ext -i
+PYTHON tester.py
+"""
+
+######## setup.py ########
+
+from Cython.Build.Dependencies import cythonize
+from distutils.core import setup
+
+setup(
+  ext_modules = cythonize("*.pyx"),
+)
+
+
+######## failure.pyx ########
+
+if globals():  # runtime True to confuse dead code removal
+    raise ImportError
+
+cdef class C:
+    cdef int a
+
+
+######## tester.py ########
+
+try:
+    try:
+        import failure  # 1
+    except ImportError:
+        import failure  # 2
+except ImportError:
+    pass
+else:
+    raise RuntimeError("ImportError was not raised on second import!")