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

Doc/whatsnew/3.10.rst

@@ -366,6 +366,10 @@ 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 now accepts NULL ``tp_doc``
+  slot.
+  (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/_lsprof.c

@@ -489,14 +489,12 @@ static PyStructSequence_Field profiler_subentry_fields[] = {
 
 static PyStructSequence_Desc profiler_entry_desc = {
     .name = "_lsprof.profiler_entry",
-    .doc = "",
     .fields = profiler_entry_fields,
     .n_in_sequence = 6
 };
 
 static PyStructSequence_Desc profiler_subentry_desc = {
     .name = "_lsprof.profiler_subentry",
-    .doc = "",
     .fields = profiler_subentry_fields,
     .n_in_sequence = 5
 };

Modules/_testcapimodule.c

@@ -3990,6 +3990,21 @@ test_structseq_newtype_doesnt_leak(PyObject *Py_UNUSED(self),
     Py_RETURN_NONE;
 }
 
+static PyType_Spec HeapDocCType_spec;
+
+static PyObject *
+test_PyType_FromSpec(PyObject *Py_UNUSED(self), PyObject *Py_UNUSED(args))
+{
+    void *tp_doc = HeapDocCType_spec.slots[0].pfunc;
+    HeapDocCType_spec.slots[0].pfunc = NULL;
+    PyObject *HeapDocCType = PyType_FromSpec(&HeapDocCType_spec);
+    assert(HeapDocCType != NULL);
+    HeapDocCType_spec.slots[0].pfunc = tp_doc;
+    Py_DECREF(HeapDocCType);
+
+    Py_RETURN_NONE;
+}
+
 static PyObject *
 test_incref_decref_API(PyObject *ob, PyObject *Py_UNUSED(ignored))
 {
@@ -5601,6 +5616,7 @@ static PyMethodDef TestMethods[] = {
     {"test_decref_doesnt_leak", test_decref_doesnt_leak,         METH_NOARGS},
     {"test_structseq_newtype_doesnt_leak",
         test_structseq_newtype_doesnt_leak, METH_NOARGS},
+    {"test_PyType_FromSpec", test_PyType_FromSpec, METH_NOARGS},
     {"test_incref_decref_API",  test_incref_decref_API,          METH_NOARGS},
     {"test_long_and_overflow",  test_long_and_overflow,          METH_NOARGS},
     {"test_long_as_double",     test_long_as_double,             METH_NOARGS},

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) {