bpo-36025: Fix PyDate_FromTimestamp API (GH-11922)

In the process of converting the date.fromtimestamp function to use
argument clinic in GH-8535, the C API for PyDate_FromTimestamp was
inadvertently changed to expect a timestamp object rather than an
argument tuple.

This PR fixes this backwards-incompatible change by adding a new wrapper
function for the C API function that unwraps the argument tuple and
passes it to the underlying function.

This PR also adds tests for both PyDate_FromTimestamp and
PyDateTime_FromTimestamp to prevent any further regressions.

Modules/_datetimemodule.c

@@ -2921,6 +2921,23 @@ datetime_date_fromtimestamp(PyTypeObject *type, PyObject *timestamp)
     return date_fromtimestamp((PyObject *) type, timestamp);
 }
 
+/* bpo-36025: This is a wrapper for API compatibility with the public C API,
+ * which expects a function that takes an *args tuple, whereas the argument
+ * clinic generates code that takes METH_O.
+ */
+static PyObject *
+datetime_date_fromtimestamp_capi(PyObject *cls, PyObject *args)
+{
+    PyObject *timestamp;
+    PyObject *result = NULL;
+
+    if (PyArg_UnpackTuple(args, "fromtimestamp", 1, 1, &timestamp)) {
+        result = date_fromtimestamp(cls, timestamp);
+    }
+
+    return result;
+}
+
 /* Return new date from proleptic Gregorian ordinal.  Raises ValueError if
  * the ordinal is out of range.
  */
@@ -6275,7 +6292,7 @@ static PyDateTime_CAPI CAPI = {
     new_delta_ex,
     new_timezone,
     datetime_fromtimestamp,
-    date_fromtimestamp,
+    datetime_date_fromtimestamp_capi,
     new_datetime_ex2,
     new_time_ex2
 };

Modules/_testcapimodule.c

@@ -2340,6 +2340,71 @@ get_timezone_utc_capi(PyObject* self, PyObject *args) {
     }
 }
 
+static PyObject *
+get_date_fromtimestamp(PyObject* self, PyObject *args)
+{
+    PyObject *tsargs = NULL, *ts = NULL, *rv = NULL;
+    int macro = 0;
+
+    if (!PyArg_ParseTuple(args, "O|p", &ts, &macro)) {
+        return NULL;
+    }
+
+    // Construct the argument tuple
+    if ((tsargs = PyTuple_Pack(1, ts)) == NULL) {
+        return NULL;
+    }
+
+    // Pass along to the API function
+    if (macro) {
+        rv = PyDate_FromTimestamp(tsargs);
+    }
+    else {
+        rv = PyDateTimeAPI->Date_FromTimestamp(
+                (PyObject *)PyDateTimeAPI->DateType, tsargs
+        );
+    }
+
+    Py_DECREF(tsargs);
+    return rv;
+}
+
+static PyObject *
+get_datetime_fromtimestamp(PyObject* self, PyObject *args)
+{
+    int macro = 0;
+    int usetz = 0;
+    PyObject *tsargs = NULL, *ts = NULL, *tzinfo = Py_None, *rv = NULL;
+    if (!PyArg_ParseTuple(args, "OO|pp", &ts, &tzinfo, &usetz, &macro)) {
+        return NULL;
+    }
+
+    // Construct the argument tuple
+    if (usetz) {
+        tsargs = PyTuple_Pack(2, ts, tzinfo);
+    }
+    else {
+        tsargs = PyTuple_Pack(1, ts);
+    }
+
+    if (tsargs == NULL) {
+        return NULL;
+    }
+
+    // Pass along to the API function
+    if (macro) {
+        rv = PyDateTime_FromTimestamp(tsargs);
+    }
+    else {
+        rv = PyDateTimeAPI->DateTime_FromTimestamp(
+                (PyObject *)PyDateTimeAPI->DateTimeType, tsargs, NULL
+        );
+    }
+
+    Py_DECREF(tsargs);
+    return rv;
+}
+
 
 /* test_thread_state spawns a thread of its own, and that thread releases
  * `thread_done` when it's finished.  The driver code has to know when the
@@ -4769,7 +4834,9 @@ static PyMethodDef TestMethods[] = {
     {"datetime_check_tzinfo",     datetime_check_tzinfo,         METH_VARARGS},
     {"make_timezones_capi",     make_timezones_capi,             METH_NOARGS},
     {"get_timezones_offset_zero",   get_timezones_offset_zero,   METH_NOARGS},
-    {"get_timezone_utc_capi",    get_timezone_utc_capi,            METH_VARARGS},
+    {"get_timezone_utc_capi",    get_timezone_utc_capi,          METH_VARARGS},
+    {"get_date_fromtimestamp",   get_date_fromtimestamp,         METH_VARARGS},
+    {"get_datetime_fromtimestamp", get_datetime_fromtimestamp,   METH_VARARGS},
     {"test_list_api",           test_list_api,                   METH_NOARGS},
     {"test_dict_iteration",     test_dict_iteration,             METH_NOARGS},
     {"dict_getitem_knownhash",  dict_getitem_knownhash,          METH_VARARGS},