bpo-45482: Rename namespaceobject.h to pycore_namespace.h (GH-28975)

Rename Include/namespaceobject.h to
Include/internal/pycore_namespace.h.

The _testmultiphase extension is now built with the
Py_BUILD_CORE_MODULE macro defined to access _PyNamespace_Type.

object.c: remove unused "pycore_context.h" include.
diff --git a/Include/Python.h b/Include/Python.h
index a2de514..c0a621a 100644
--- a/Include/Python.h
+++ b/Include/Python.h
@@ -77,7 +77,6 @@
 #include "warnings.h"
 #include "weakrefobject.h"
 #include "structseq.h"
-#include "namespaceobject.h"
 #include "cpython/picklebufobject.h"
 #include "cpython/pytime.h"
 #include "codecs.h"
diff --git a/Include/internal/pycore_namespace.h b/Include/internal/pycore_namespace.h
new file mode 100644
index 0000000..cb76f04
--- /dev/null
+++ b/Include/internal/pycore_namespace.h
@@ -0,0 +1,20 @@
+// Simple namespace object interface
+
+#ifndef Py_INTERNAL_NAMESPACE_H
+#define Py_INTERNAL_NAMESPACE_H
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#ifndef Py_BUILD_CORE
+#  error "this header requires Py_BUILD_CORE define"
+#endif
+
+PyAPI_DATA(PyTypeObject) _PyNamespace_Type;
+
+PyAPI_FUNC(PyObject *) _PyNamespace_New(PyObject *kwds);
+
+#ifdef __cplusplus
+}
+#endif
+#endif  // !Py_INTERNAL_NAMESPACE_H
diff --git a/Include/namespaceobject.h b/Include/namespaceobject.h
deleted file mode 100644
index 0c8d95c..0000000
--- a/Include/namespaceobject.h
+++ /dev/null
@@ -1,19 +0,0 @@
-
-/* simple namespace object interface */
-
-#ifndef NAMESPACEOBJECT_H
-#define NAMESPACEOBJECT_H
-#ifdef __cplusplus
-extern "C" {
-#endif
-
-#ifndef Py_LIMITED_API
-PyAPI_DATA(PyTypeObject) _PyNamespace_Type;
-
-PyAPI_FUNC(PyObject *) _PyNamespace_New(PyObject *kwds);
-#endif /* !Py_LIMITED_API */
-
-#ifdef __cplusplus
-}
-#endif
-#endif /* !NAMESPACEOBJECT_H */
diff --git a/Makefile.pre.in b/Makefile.pre.in
index b79b71f..9de5171 100644
--- a/Makefile.pre.in
+++ b/Makefile.pre.in
@@ -1151,7 +1151,6 @@
 		$(srcdir)/Include/methodobject.h \
 		$(srcdir)/Include/modsupport.h \
 		$(srcdir)/Include/moduleobject.h \
-		$(srcdir)/Include/namespaceobject.h \
 		$(srcdir)/Include/object.h \
 		$(srcdir)/Include/objimpl.h \
 		$(srcdir)/Include/opcode.h \
@@ -1261,6 +1260,7 @@
 		$(srcdir)/Include/internal/pycore_list.h \
 		$(srcdir)/Include/internal/pycore_long.h \
 		$(srcdir)/Include/internal/pycore_moduleobject.h \
+		$(srcdir)/Include/internal/pycore_namespace.h \
 		$(srcdir)/Include/internal/pycore_object.h \
 		$(srcdir)/Include/internal/pycore_pathconfig.h \
 		$(srcdir)/Include/internal/pycore_pyarena.h \
diff --git a/Modules/_testcapimodule.c b/Modules/_testcapimodule.c
index 7cbd2dc..82cfc04 100644
--- a/Modules/_testcapimodule.c
+++ b/Modules/_testcapimodule.c
@@ -1167,8 +1167,8 @@
     assert(strcmp(PyUnicode_AsUTF8(tp_qualname), "int") == 0);
     Py_DECREF(tp_qualname);
 
-    tp_qualname = PyType_GetQualName(&_PyNamespace_Type);
-    assert(strcmp(PyUnicode_AsUTF8(tp_qualname), "SimpleNamespace") == 0);
+    tp_qualname = PyType_GetQualName(&PyODict_Type);
+    assert(strcmp(PyUnicode_AsUTF8(tp_qualname), "OrderedDict") == 0);
     Py_DECREF(tp_qualname);
 
     PyObject *HeapTypeNameType = PyType_FromSpec(&HeapTypeNameType_Spec);
diff --git a/Modules/_testmultiphase.c b/Modules/_testmultiphase.c
index e0ed77d..2d25e16 100644
--- a/Modules/_testmultiphase.c
+++ b/Modules/_testmultiphase.c
@@ -3,6 +3,7 @@
  */
 
 #include "Python.h"
+#include "pycore_namespace.h"     // _PyNamespace_New()
 
 /* State for testing module state access from methods */
 
diff --git a/Modules/timemodule.c b/Modules/timemodule.c
index ca8d62d..0ef3b2f 100644
--- a/Modules/timemodule.c
+++ b/Modules/timemodule.c
@@ -2,6 +2,7 @@
 
 #include "Python.h"
 #include "pycore_fileutils.h"     // _Py_BEGIN_SUPPRESS_IPH
+#include "pycore_namespace.h"     // _PyNamespace_New()
 
 #include <ctype.h>
 
diff --git a/Objects/namespaceobject.c b/Objects/namespaceobject.c
index fa37ed2..7875e7c 100644
--- a/Objects/namespaceobject.c
+++ b/Objects/namespaceobject.c
@@ -1,6 +1,7 @@
 // namespace object implementation
 
 #include "Python.h"
+#include "pycore_namespace.h"     // _PyNamespace_Type
 #include "structmember.h"         // PyMemberDef
 
 
diff --git a/Objects/object.c b/Objects/object.c
index 5e719d4..25f5a21 100644
--- a/Objects/object.c
+++ b/Objects/object.c
@@ -4,10 +4,10 @@
 #include "Python.h"
 #include "pycore_call.h"          // _PyObject_CallNoArgs()
 #include "pycore_ceval.h"         // _Py_EnterRecursiveCall()
-#include "pycore_context.h"
-#include "pycore_dict.h"
+#include "pycore_dict.h"          // _PyObject_MakeDictFromInstanceAttributes()
 #include "pycore_floatobject.h"   // _PyFloat_DebugMallocStats()
 #include "pycore_initconfig.h"    // _PyStatus_EXCEPTION()
+#include "pycore_namespace.h"     // _PyNamespace_Type
 #include "pycore_object.h"        // _PyType_CheckConsistency()
 #include "pycore_pyerrors.h"      // _PyErr_Occurred()
 #include "pycore_pylifecycle.h"   // _PyTypes_InitSlotDefs()
diff --git a/PCbuild/pythoncore.vcxproj b/PCbuild/pythoncore.vcxproj
index 357d0a7..015d783 100644
--- a/PCbuild/pythoncore.vcxproj
+++ b/PCbuild/pythoncore.vcxproj
@@ -202,6 +202,7 @@
     <ClInclude Include="..\Include\internal\pycore_list.h" />
     <ClInclude Include="..\Include\internal\pycore_long.h" />
     <ClInclude Include="..\Include\internal\pycore_moduleobject.h" />
+    <ClInclude Include="..\Include\internal\pycore_namespace.h" />
     <ClInclude Include="..\Include\internal\pycore_object.h" />
     <ClInclude Include="..\Include\internal\pycore_pathconfig.h" />
     <ClInclude Include="..\Include\internal\pycore_pyarena.h" />
@@ -229,7 +230,6 @@
     <ClInclude Include="..\Include\methodobject.h" />
     <ClInclude Include="..\Include\modsupport.h" />
     <ClInclude Include="..\Include\moduleobject.h" />
-    <ClInclude Include="..\Include\namespaceobject.h" />
     <ClInclude Include="..\Include\object.h" />
     <ClInclude Include="..\Include\objimpl.h" />
     <ClInclude Include="..\Include\opcode.h" />
diff --git a/PCbuild/pythoncore.vcxproj.filters b/PCbuild/pythoncore.vcxproj.filters
index 1a3ad88..94528b9 100644
--- a/PCbuild/pythoncore.vcxproj.filters
+++ b/PCbuild/pythoncore.vcxproj.filters
@@ -327,9 +327,6 @@
     <ClInclude Include="..\Include\pyhash.h">
       <Filter>Include</Filter>
     </ClInclude>
-    <ClInclude Include="..\Include\namespaceobject.h">
-      <Filter>Include</Filter>
-    </ClInclude>
     <ClInclude Include="..\Modules\hashtable.h">
       <Filter>Modules</Filter>
     </ClInclude>
@@ -558,6 +555,9 @@
     <ClInclude Include="..\Include\internal\pycore_moduleobject.h">
       <Filter>Include\internal</Filter>
     </ClInclude>
+    <ClInclude Include="..\Include\internal\pycore_namespace.h">
+      <Filter>Include</Filter>
+    </ClInclude>
     <ClInclude Include="..\Include\internal\pycore_object.h">
       <Filter>Include\internal</Filter>
     </ClInclude>
diff --git a/Python/import.c b/Python/import.c
index f216092..fe4686c 100644
--- a/Python/import.c
+++ b/Python/import.c
@@ -3,19 +3,19 @@
 #include "Python.h"
 
 #include "pycore_import.h"        // _PyImport_BootstrapImp()
-#include "pycore_initconfig.h"
-#include "pycore_pyerrors.h"
-#include "pycore_pyhash.h"
+#include "pycore_initconfig.h"    // _PyStatus_OK()
+#include "pycore_interp.h"        // _PyInterpreterState_ClearModules()
+#include "pycore_namespace.h"     // _PyNamespace_Type
+#include "pycore_pyerrors.h"      // _PyErr_SetString()
+#include "pycore_pyhash.h"        // _Py_KeyedHash()
 #include "pycore_pylifecycle.h"
 #include "pycore_pymem.h"         // _PyMem_SetDefaultAllocator()
-#include "pycore_interp.h"        // _PyInterpreterState_ClearModules()
 #include "pycore_pystate.h"       // _PyInterpreterState_GET()
-#include "pycore_sysmodule.h"
-#include "marshal.h"
-#include "code.h"
-#include "importdl.h"
-#include "pydtrace.h"
-#include <stdbool.h>
+#include "pycore_sysmodule.h"     // _PySys_Audit()
+#include "marshal.h"              // PyMarshal_ReadObjectFromString()
+#include "importdl.h"             // _PyImport_DynLoadFiletab
+#include "pydtrace.h"             // PyDTrace_IMPORT_FIND_LOAD_START_ENABLED()
+#include <stdbool.h>              // bool
 
 #ifdef HAVE_FCNTL_H
 #include <fcntl.h>
diff --git a/Python/sysmodule.c b/Python/sysmodule.c
index ae3cbf1..ad9be71 100644
--- a/Python/sysmodule.c
+++ b/Python/sysmodule.c
@@ -20,6 +20,7 @@
 #include "pycore_code.h"          // _Py_QuickenedCount
 #include "pycore_frame.h"         // InterpreterFrame
 #include "pycore_initconfig.h"    // _PyStatus_EXCEPTION()
+#include "pycore_namespace.h"     // _PyNamespace_New()
 #include "pycore_object.h"        // _PyObject_IS_GC()
 #include "pycore_pathconfig.h"    // _PyPathConfig_ComputeSysPath0()
 #include "pycore_pyerrors.h"      // _PyErr_Fetch()
diff --git a/setup.py b/setup.py
index 56c06cb..24365ef 100644
--- a/setup.py
+++ b/setup.py
@@ -1043,7 +1043,8 @@
         self.add(Extension('_testimportmultiple', ['_testimportmultiple.c']))
 
         # Test multi-phase extension module init (PEP 489)
-        self.add(Extension('_testmultiphase', ['_testmultiphase.c']))
+        self.add(Extension('_testmultiphase', ['_testmultiphase.c'],
+                           extra_compile_args=['-DPy_BUILD_CORE_MODULE']))
 
         # Fuzz tests.
         self.add(Extension('_xxtestfuzz',