bpo-35081: Remove Py_BUILD_CORE from datetime.h (GH-10416)

Datetime macros like PyDate_Check() have two implementations, one using
the C API capsule and one using direct access to the datetime type
symbols defined in _datetimemodule.c. Since the direct access versions
of the macros are only used in _datetimemodule.c, they have been moved
out of "datetime.h" and into _datetimemodule.c.

The _PY_DATETIME_IMPL macro is currently necessary in order to avoid
both duplicate definitions of these macros in _datetimemodule.c and
unnecessary declarations of C API capsule-related macros and varibles in
datetime.h.
Co-Authored-By: Victor Stinner <vstinner@redhat.com>

Include/datetime.h

@@ -180,26 +180,11 @@ typedef struct {
 #define PyDateTime_CAPSULE_NAME "datetime.datetime_CAPI"
 
 
-#ifdef Py_BUILD_CORE
-
-/* Macros for type checking when building the Python core. */
-#define PyDate_Check(op) PyObject_TypeCheck(op, &PyDateTime_DateType)
-#define PyDate_CheckExact(op) (Py_TYPE(op) == &PyDateTime_DateType)
-
-#define PyDateTime_Check(op) PyObject_TypeCheck(op, &PyDateTime_DateTimeType)
-#define PyDateTime_CheckExact(op) (Py_TYPE(op) == &PyDateTime_DateTimeType)
-
-#define PyTime_Check(op) PyObject_TypeCheck(op, &PyDateTime_TimeType)
-#define PyTime_CheckExact(op) (Py_TYPE(op) == &PyDateTime_TimeType)
-
-#define PyDelta_Check(op) PyObject_TypeCheck(op, &PyDateTime_DeltaType)
-#define PyDelta_CheckExact(op) (Py_TYPE(op) == &PyDateTime_DeltaType)
-
-#define PyTZInfo_Check(op) PyObject_TypeCheck(op, &PyDateTime_TZInfoType)
-#define PyTZInfo_CheckExact(op) (Py_TYPE(op) == &PyDateTime_TZInfoType)
-
-#else
-
+/* This block is only used as part of the public API and should not be
+ * included in _datetimemodule.c, which does not use the C API capsule.
+ * See bpo-35081 for more details.
+ * */
+#ifndef _PY_DATETIME_IMPL
 /* Define global variable for the C API and a macro for setting it. */
 static PyDateTime_CAPI *PyDateTimeAPI = NULL;
 
@@ -225,6 +210,7 @@ static PyDateTime_CAPI *PyDateTimeAPI = NULL;
 #define PyTZInfo_Check(op) PyObject_TypeCheck(op, PyDateTimeAPI->TZInfoType)
 #define PyTZInfo_CheckExact(op) (Py_TYPE(op) == PyDateTimeAPI->TZInfoType)
 
+
 /* Macros for accessing constructors in a simplified fashion. */
 #define PyDate_FromDate(year, month, day) \
     PyDateTimeAPI->Date_FromDate(year, month, day, PyDateTimeAPI->DateType)
@@ -264,7 +250,7 @@ static PyDateTime_CAPI *PyDateTimeAPI = NULL;
     PyDateTimeAPI->Date_FromTimestamp( \
         (PyObject*) (PyDateTimeAPI->DateType), args)
 
-#endif  /* Py_BUILD_CORE */
+#endif   /* !defined(_PY_DATETIME_IMPL) */
 
 #ifdef __cplusplus
 }

Modules/_datetimemodule.c

@@ -2,7 +2,13 @@
  *  http://www.zope.org/Members/fdrake/DateTimeWiki/FrontPage
  */
 
+/* bpo-35081: Defining this prevents including the C API capsule;
+ * internal versions of the  Py*_Check macros which do not require
+ * the capsule are defined below */
+#define _PY_DATETIME_IMPL
+
 #include "Python.h"
+#include "datetime.h"
 #include "structmember.h"
 
 #include <time.h>
@@ -11,14 +17,21 @@
 #  include <winsock2.h>         /* struct timeval */
 #endif
 
-/* Differentiate between building the core module and building extension
- * modules.
- */
-#ifndef Py_BUILD_CORE
-#define Py_BUILD_CORE
-#endif
-#include "datetime.h"
-#undef Py_BUILD_CORE
+#define PyDate_Check(op) PyObject_TypeCheck(op, &PyDateTime_DateType)
+#define PyDate_CheckExact(op) (Py_TYPE(op) == &PyDateTime_DateType)
+
+#define PyDateTime_Check(op) PyObject_TypeCheck(op, &PyDateTime_DateTimeType)
+#define PyDateTime_CheckExact(op) (Py_TYPE(op) == &PyDateTime_DateTimeType)
+
+#define PyTime_Check(op) PyObject_TypeCheck(op, &PyDateTime_TimeType)
+#define PyTime_CheckExact(op) (Py_TYPE(op) == &PyDateTime_TimeType)
+
+#define PyDelta_Check(op) PyObject_TypeCheck(op, &PyDateTime_DeltaType)
+#define PyDelta_CheckExact(op) (Py_TYPE(op) == &PyDateTime_DeltaType)
+
+#define PyTZInfo_Check(op) PyObject_TypeCheck(op, &PyDateTime_TZInfoType)
+#define PyTZInfo_CheckExact(op) (Py_TYPE(op) == &PyDateTime_TZInfoType)
+
 
 /*[clinic input]
 module datetime