Fix crash when extending from proxy (#1100)

Author: asvetlov

CHANGES/1100.bugfix

@@ -0,0 +1 @@
+Fixed a crash when extending a multidict from multidict proxy if C Extensions were used.

multidict/_multidict.c

@@ -227,7 +227,11 @@ _multidict_extend_with_args(MultiDictObject *self, PyObject *arg,
 
     if (PyObject_HasAttrString(arg, "items")) {
         if (_MultiDict_Check(arg)) {
-            arg_items = multidict_items((MultiDictObject*)arg);
+            if (MultiDict_CheckExact(arg) || CIMultiDict_CheckExact(arg)) {
+                arg_items = multidict_items((MultiDictObject*)arg);
+            } else if (MultiDictProxy_CheckExact(arg) || CIMultiDictProxy_CheckExact(arg)) {
+                arg_items = multidict_items(((MultiDictProxyObject*)arg)->md);
+            }
         } else {
             arg_items = PyMapping_Items(arg);
         }

multidict/_multilib/iter.h

@@ -81,6 +81,8 @@ multidict_items_iter_iternext(MultidictIter *self)
         return NULL;
     }
     if (res == 0) {
+        Py_CLEAR(key);
+        Py_CLEAR(value);
         PyErr_SetNone(PyExc_StopIteration);
         return NULL;
     }

multidict/_multilib/pair_list.h

@@ -421,10 +421,22 @@ pair_list_next(pair_list_t *list, pair_list_pos_t *pos,
                PyObject **pkey, PyObject **pvalue)
 {
     if (pos->pos >= list->size) {
+        if (pkey) {
+            *pkey = NULL;
+        }
+        if (pvalue) {
+            *pvalue = NULL;
+        }
         return 0;
     }
 
     if (pos->version != list->version) {
+        if (pkey) {
+            *pkey = NULL;
+        }
+        if (pvalue) {
+            *pvalue = NULL;
+        }
         PyErr_SetString(PyExc_RuntimeError, "MultiDict changed during iteration");
         return -1;
     }

tests/test_multidict.py

@@ -793,6 +793,14 @@ def test_basics(self, cls: type[CIMultiDict[str]]) -> None:
         with pytest.raises(KeyError, match="key2"):
             d.getone("key2")
 
+    def test_from_md_and_kwds(self, cls: type[CIMultiDict[str]]) -> None:
+        d = cls([("KEY", "value1")])
+        d2 = cls(d, KEY="value2")
+
+        print(type(d))
+
+        assert list(d2.items()) == [("KEY", "value1"), ("KEY", "value2")]
+
     def test_getall(self, cls: type[CIMultiDict[str]]) -> None:
         d = cls([("KEY", "value1")], KEY="value2")