Fix external reference assignment

Cython/Compiler/Code.py

@@ -1738,6 +1738,12 @@ class CCodeWriter(object):
             self.putln("%s_%sDECREF(%s);" % (
                 prefix, X, self.as_pyobject(cname, type)))
 
+    def put_decref_set(self, cname, rhs_cname):
+        self.putln("__Pyx_DECREF_SET(%s, %s);" % (cname, rhs_cname))
+
+    def put_xdecref_set(self, cname, rhs_cname):
+        self.putln("__Pyx_XDECREF_SET(%s, %s);" % (cname, rhs_cname))
+
     def put_var_decref(self, entry):
         if entry.type.is_pyobject:
             self.putln("__Pyx_XDECREF(%s);" % self.entry_as_pyobject(entry))

Cython/Compiler/ExprNodes.py

@@ -1883,7 +1883,7 @@ class NameNode(AtomicExprNode):
                 # variables that the acquired buffer info is stored to is allocated
                 # per entry and coupled with it.
                 self.generate_acquire_buffer(rhs, code)
-
+            assigned = False
             if self.type.is_pyobject:
                 #print "NameNode.generate_assignment_code: to", self.name ###
                 #print "...from", rhs ###
@@ -1898,18 +1898,26 @@ class NameNode(AtomicExprNode):
                                 code.put_xgotref(self.py_result())
                             else:
                                 code.put_gotref(self.py_result())
+                    assigned = True
                     if entry.is_cglobal:
-                        code.put_decref(self.result(), self.ctype())
+                        code.put_decref_set(
+                            self.result(), rhs.result_as(self.ctype()))
                     else:
                         if not self.cf_is_null:
                             if self.cf_maybe_null:
-                                code.put_xdecref(self.result(), self.ctype())
+                                code.put_xdecref_set(
+                                    self.result(), rhs.result_as(self.ctype()))
                             else:
-                                code.put_decref(self.result(), self.ctype())
+                                code.put_decref_set(
+                                    self.result(), rhs.result_as(self.ctype()))
+                        else:
+                            assigned = False
                     if is_external_ref:
                         code.put_giveref(rhs.py_result())
             if not self.type.is_memoryviewslice:
-                code.putln('%s = %s;' % (self.result(), rhs.result_as(self.ctype())))
+                if not assigned:
+                    code.putln('%s = %s;' % (
+                        self.result(), rhs.result_as(self.ctype())))
                 if debug_disposal_code:
                     print("NameNode.generate_assignment_code:")
                     print("...generating post-assignment code for %s" % rhs)

Cython/Utility/ModuleSetupCode.c

@@ -531,6 +531,15 @@ static int __Pyx_check_binary_version(void) {
   #define __Pyx_XGIVEREF(r)
 #endif /* CYTHON_REFNANNY */
 
+#define __Pyx_XDECREF_SET(r, v) do {                            \
+        PyObject *tmp = (PyObject *) r;                         \
+        r = v; __Pyx_XDECREF(tmp);                              \
+    } while (0)
+#define __Pyx_DECREF_SET(r, v) do {                             \
+        PyObject *tmp = (PyObject *) r;                         \
+        r = v; __Pyx_DECREF(tmp);                               \
+    } while (0)
+
 #define __Pyx_CLEAR(r)    do { PyObject* tmp = ((PyObject*)(r)); r = NULL; __Pyx_DECREF(tmp);} while(0)
 #define __Pyx_XCLEAR(r)   do { if((r) != NULL) {PyObject* tmp = ((PyObject*)(r)); r = NULL; __Pyx_DECREF(tmp);}} while(0)
 

tests/run/external_ref_reassignment.pyx

+# Test that variable visible outside of the local scope (e.g. closure, cglobals)
+# is set before original value is decrefed.
+cdef object g
+
+def test_cglobals_reassignment():
+    """
+    >>> test_cglobals_reassignment()
+    1234
+    """
+    global g
+    class Special:
+        def __del__(self):
+            print g
+    g = (Special(),)
+    g = 1234
+
+def test_closure_reassignment():
+    """
+    >>> test_closure_reassignment()
+    4321
+    """
+    class Special:
+        def __del__(self):
+            print c
+    c = (Special(),)
+    c = 4321