bpo-41832: PyType_FromModuleAndSpec() can accept the NULL tp_doc slot.

Doc/whatsnew/3.10.rst

@@ -366,6 +366,9 @@ New Features
 * Added :c:func:`PyUnicode_AsUTF8AndSize` to the limited C API.
   (Contributed by Alex Gaynor in :issue:`41784`.)
 
+* The :c:func:`PyType_FromModuleAndSpec` function can accept tp_doc=NULL.
+  (Contributed by Hai Shi in :issue:`41832`.)
+
 
 Porting to Python 3.10
 ----------------------

Misc/NEWS.d/next/C API/2020-11-03-19-47-06.bpo-41832.dL1VJJ.rst

@@ -0,0 +1 @@
+:c:func:`PyType_FromModuleAndSpec` can accept tp_doc=NULL.

Modules/_testcapimodule.c

@@ -3987,6 +3987,11 @@ test_structseq_newtype_doesnt_leak(PyObject *Py_UNUSED(self),
     assert(PyType_FastSubclass(structseq_type, Py_TPFLAGS_TUPLE_SUBCLASS));
     Py_DECREF(structseq_type);
 
+    descr.doc = NULL;
+    structseq_type = PyStructSequence_NewType(&descr);
+    assert(structseq_type != NULL);
+    Py_DECREF(structseq_type);
+
     Py_RETURN_NONE;
 }
 

Objects/typeobject.c

@@ -3012,6 +3012,12 @@ PyType_FromModuleAndSpec(PyObject *module, PyType_Spec *spec, PyObject *bases)
         else if (slot->slot == Py_tp_doc) {
             /* For the docstring slot, which usually points to a static string
                literal, we need to make a copy */
+
+            /* bpo-41832: PyType_FromModuleAndSpec() can accept tp_doc=NULL. */
+            if (slot->pfunc == NULL) {
+                type->tp_doc = NULL;
+                continue;
+            }
             size_t len = strlen(slot->pfunc)+1;
             char *tp_doc = PyObject_MALLOC(len);
             if (tp_doc == NULL) {