Fix reference counting of memoryview arguments to special functions

Fixes cython#5571.

I believe this is to any function with a special signature
(essentially most dunder methods of cdef classes). The specific
report was about properties though.

Cython/Compiler/Nodes.py

@@ -2170,6 +2170,9 @@ def generate_function_definitions(self, env, code):
                                     have_gil=code.funcstate.gil_owned)
         for entry in lenv.var_entries:
             if entry.is_arg and entry.cf_is_reassigned and not entry.in_closure:
+                if entry.type.is_memoryviewslice:
+                    code.put_var_incref_memoryviewslice(entry,
+                                        have_gil=code.funcstate.gil_owned)
                 if entry.xdecref_cleanup:
                     code.put_var_xincref(entry)
                 else:
@@ -2357,10 +2360,9 @@ def align_error_path_gil_to_success_path(): pass
             if not entry.used or entry.in_closure:
                 continue
 
-            if entry.type.is_pyobject:
+            if entry.type.needs_refcounting:
                 if entry.is_arg and not entry.cf_is_reassigned:
                     continue
-            if entry.type.needs_refcounting:
                 assure_gil('success')
             # FIXME ideally use entry.xdecref_cleanup but this currently isn't reliable
             code.put_var_xdecref(entry, have_gil=gil_owned['success'])
@@ -3729,13 +3731,12 @@ def generate_function_definitions(self, env, code):
 
         # ----- Non-error return cleanup
         code.put_label(code.return_label)
-        for entry in lenv.var_entries:
-            if entry.is_arg:
-                # mainly captures the star/starstar args
-                if entry.xdecref_cleanup:
-                    code.put_var_xdecref(entry)
+        for arg in [self.star_arg, self.starstar_arg]:
+            if arg and arg.entry.is_arg:
+                if arg.entry.xdecref_cleanup:
+                    code.put_var_xdecref(arg.entry)
                 else:
-                    code.put_var_decref(entry)
+                    code.put_var_decref(arg.entry)
         for arg in self.args:
             if not arg.type.is_pyobject:
                 # This captures anything that's been converted from a PyObject.

tests/memoryview/memoryview.pyx

@@ -978,6 +978,46 @@ def test_acquire_memoryview_slice():
     print b[2, 4]
     print c[2, 4]
 
+cdef class TestPassMemoryviewToSetter:
+    """
+    Setter has a fixed function signature and the
+    argument needs conversion so it ends up passing through
+    some slightly different reference counting code
+
+    >>> dmb = DoubleMockBuffer("dmb", range(2), shape=(2,))
+    >>> TestPassMemoryviewToSetter().prop = dmb
+    acquired dmb
+    In prop setter
+    released dmb
+    >>> TestPassMemoryviewToSetter().prop_with_reassignment = dmb
+    acquired dmb
+    In prop_with_reassignment setter
+    released dmb
+    >>> dmb = DoubleMockBuffer("dmb", range(1,3), shape=(2,))
+    >>> TestPassMemoryviewToSetter().prop_with_reassignment = dmb
+    acquired dmb
+    In prop_with_reassignment setter
+    released dmb
+    """
+    @property
+    def prop(self):
+        return None
+
+    @prop.setter
+    def prop(self, double[:] x):
+        print("In prop setter")
+
+    @property
+    def prop_with_reassignment(self):
+        return None
+
+    @prop_with_reassignment.setter
+    def prop_with_reassignment(self, double[:] x):
+        # reassignment again requires slightly different code
+        if x[0]:
+            x = x[1:]
+        print("In prop_with_reassignment setter")
+
 class SingleObject(object):
     def __init__(self, value):
         self.value = value