Fixed handling of kwds in generator closures (GH-3268)

Cython/Compiler/Nodes.py

@@ -3256,8 +3256,14 @@ class DefNode(FuncDefNode):
         def put_into_closure(entry):
             if entry.in_closure:
                 code.putln('%s = %s;' % (entry.cname, entry.original_cname))
-                code.put_var_incref(entry)
-                code.put_var_giveref(entry)
+                if entry.xdecref_cleanup:
+                    # mostly applies to the starstar arg - this can sometimes be NULL
+                    # so must be xincrefed instead
+                    code.put_var_xincref(entry)
+                    code.put_var_xgiveref(entry)
+                else:
+                    code.put_var_incref(entry)
+                    code.put_var_giveref(entry)
         for arg in self.args:
             put_into_closure(arg.entry)
         for arg in self.star_arg, self.starstar_arg:

tests/run/generators.pyx

@@ -522,3 +522,37 @@ def test_generator_frame(a=1):
     """
     b = a + 1
     yield b
+
+# GH Issue 3265 - **kwds could cause a crash in some cases due to not
+# handling NULL pointers (in testing it shows as a REFNANNY error).
+# This was on creation of the generator and
+# doesn't really require it to be iterated through:
+def some_function():
+    return 0
+
+def test_generator_kwds1(**kwargs):
+    """
+    >>> for a in test_generator_kwds1():
+    ...     print(a)
+    0
+    """
+    yield some_function(**kwargs)
+
+def test_generator_kwds2(**kwargs):
+    """
+    >>> for a in test_generator_kwds2():
+    ...     print(a)
+    0
+    """
+    yield 0
+
+def test_generator_kwds3(**kwargs):
+    """
+    This didn't actually crash before but is still worth a try
+    >>> len(list(test_generator_kwds3()))
+    0
+    >>> for a in test_generator_kwds3(a=1):
+    ...    print(a)
+    a
+    """
+    yield from kwargs.keys()