Work around error "__reduce_cython__ cannot be found" (GH-3549)

* Work around error that "__reduce_cython__ cannot be found" when re-importing an extension module that was already initialised before.
* Exclude "reimport_failure" test in Py2 and PyPy since Py2 does not allow reimports and PyPy3 apparently does nothing for them.

Closes #3545.

Cython/Utility/ExtensionTypes.c

@@ -235,16 +235,28 @@ 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_GetAttrStrNoError(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);
         }

runtests.py

@@ -417,6 +417,7 @@ VER_DEP_MODULES = {
                                            'run.test_raisefrom',
                                            'run.different_package_names',
                                            'run.unicode_imports',  # encoding problems on appveyor in Py2
+                                           '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

@@ -38,6 +38,7 @@ run.index
 run.pyclass_special_methods
 run.reimport_from_package
 run.reimport_from_subinterpreter
+run.reimport_failure
 pkg.cimportfrom
 embedded
 TestCyCache

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!")