gh-110964: Remove private _PyArg functions (#110966)

Move the following private functions and structures to
pycore_modsupport.h internal C API:

* _PyArg_BadArgument()
* _PyArg_CheckPositional()
* _PyArg_NoKeywords()
* _PyArg_NoPositional()
* _PyArg_ParseStack()
* _PyArg_ParseStackAndKeywords()
* _PyArg_Parser structure
* _PyArg_UnpackKeywords()
* _PyArg_UnpackKeywordsWithVararg()
* _PyArg_UnpackStack()
* _Py_ANY_VARARGS()

Changes:

* Python/getargs.h now includes pycore_modsupport.h to export
  functions.
* clinic.py now adds pycore_modsupport.h when one of these functions
  is used.
* Add pycore_modsupport.h includes when a C extension uses one of
  these functions.
* Define Py_BUILD_CORE_MODULE in C extensions which now include
  directly or indirectly (via code generated by Argument Clinic)
  pycore_modsupport.h:

  * _csv
  * _curses_panel
  * _dbm
  * _gdbm
  * _multiprocessing.posixshmem
  * _sqlite.row
  * _statistics
  * grp
  * resource
  * syslog

* _testcapi: bad_get() no longer uses METH_FASTCALL calling
  convention but METH_VARARGS. Replace _PyArg_UnpackStack() with
  PyArg_ParseTuple().
* _testcapi: add PYTESTCAPI_NEED_INTERNAL_API macro which is defined
  by _testcapi sub-modules which need the internal C API
  (pycore_modsupport.h): exceptions.c, float.c, vectorcall.c,
  watchers.c.
* Remove Include/cpython/modsupport.h header file.
  Include/modsupport.h no longer includes the removed header file.
* Fix mypy clinic.py

9 files changed, 41 insertions, 16 deletions

diff --git a/Modules/_testcapi/clinic/exceptions.c.h b/Modules/_testcapi/clinic/exceptions.c.h
index 39b5f8b..a797444 100644
--- a/Modules/_testcapi/clinic/exceptions.c.h
+++ b/Modules/_testcapi/clinic/exceptions.c.h
@@ -6,6 +6,7 @@ preserve
 #  include "pycore_gc.h"          // PyGC_Head
 #  include "pycore_runtime.h"     // _Py_ID()
 #endif
+#include "pycore_modsupport.h"    // _PyArg_CheckPositional()
 
 PyDoc_STRVAR(_testcapi_err_set_raised__doc__,
 "err_set_raised($module, exception, /)\n"
@@ -455,4 +456,4 @@ _testcapi_unstable_exc_prep_reraise_star(PyObject *module, PyObject *const *args
 exit:
     return return_value;
 }
-/*[clinic end generated code: output=ff19512450b3bbdb input=a9049054013a1b77]*/
+/*[clinic end generated code: output=0b11ef105030a48e input=a9049054013a1b77]*/
diff --git a/Modules/_testcapi/clinic/float.c.h b/Modules/_testcapi/clinic/float.c.h
index fb0931a..d5a00c8 100644
--- a/Modules/_testcapi/clinic/float.c.h
+++ b/Modules/_testcapi/clinic/float.c.h
@@ -2,6 +2,8 @@
 preserve
 [clinic start generated code]*/
 
+#include "pycore_modsupport.h"    // _PyArg_CheckPositional()
+
 PyDoc_STRVAR(_testcapi_float_pack__doc__,
 "float_pack($module, size, d, le, /)\n"
 "--\n"
@@ -79,4 +81,4 @@ _testcapi_float_unpack(PyObject *module, PyObject *const *args, Py_ssize_t nargs
 exit:
     return return_value;
 }
-/*[clinic end generated code: output=50146051f1341cce input=a9049054013a1b77]*/
+/*[clinic end generated code: output=b43dfd3a77fe04ba input=a9049054013a1b77]*/
diff --git a/Modules/_testcapi/clinic/vectorcall.c.h b/Modules/_testcapi/clinic/vectorcall.c.h
index 48688e9..c6049a4 100644
--- a/Modules/_testcapi/clinic/vectorcall.c.h
+++ b/Modules/_testcapi/clinic/vectorcall.c.h
@@ -2,6 +2,8 @@
 preserve
 [clinic start generated code]*/
 
+#include "pycore_modsupport.h"    // _PyArg_CheckPositional()
+
 PyDoc_STRVAR(_testcapi_pyobject_fastcalldict__doc__,
 "pyobject_fastcalldict($module, func, func_args, kwargs, /)\n"
 "--\n"
@@ -204,4 +206,4 @@ _testcapi_has_vectorcall_flag(PyObject *module, PyObject *arg)
 exit:
     return return_value;
 }
-/*[clinic end generated code: output=0667266b825ec9ec input=a9049054013a1b77]*/
+/*[clinic end generated code: output=210ae67caab177ba input=a9049054013a1b77]*/
diff --git a/Modules/_testcapi/clinic/watchers.c.h b/Modules/_testcapi/clinic/watchers.c.h
index fd2ef60..ebd71d1 100644
--- a/Modules/_testcapi/clinic/watchers.c.h
+++ b/Modules/_testcapi/clinic/watchers.c.h
@@ -2,6 +2,8 @@
 preserve
 [clinic start generated code]*/
 
+#include "pycore_modsupport.h"    // _PyArg_CheckPositional()
+
 PyDoc_STRVAR(_testcapi_watch_dict__doc__,
 "watch_dict($module, watcher_id, dict, /)\n"
 "--\n"
@@ -189,4 +191,4 @@ _testcapi_set_func_kwdefaults_via_capi(PyObject *module, PyObject *const *args,
 exit:
     return return_value;
 }
-/*[clinic end generated code: output=5ad5771d6b29dfb9 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=0e07ce7f295917a5 input=a9049054013a1b77]*/
diff --git a/Modules/_testcapi/exceptions.c b/Modules/_testcapi/exceptions.c
index b54ce0c..e463e62 100644
--- a/Modules/_testcapi/exceptions.c
+++ b/Modules/_testcapi/exceptions.c
@@ -1,3 +1,6 @@
+// clinic/exceptions.c.h uses internal pycore_modsupport.h API
+#define PYTESTCAPI_NEED_INTERNAL_API
+
 #include "parts.h"
 #include "util.h"
 #include "clinic/exceptions.c.h"
diff --git a/Modules/_testcapi/float.c b/Modules/_testcapi/float.c
index cff53fb..2a7d979 100644
--- a/Modules/_testcapi/float.c
+++ b/Modules/_testcapi/float.c
@@ -1,3 +1,6 @@
+// clinic/float.c.h uses internal pycore_modsupport.h API
+#define PYTESTCAPI_NEED_INTERNAL_API
+
 #include "parts.h"
 #include "clinic/float.c.h"
 
diff --git a/Modules/_testcapi/parts.h b/Modules/_testcapi/parts.h
index acdba86..e5dbb9c 100644
--- a/Modules/_testcapi/parts.h
+++ b/Modules/_testcapi/parts.h
@@ -4,21 +4,27 @@
 // Always enable assertions
 #undef NDEBUG
 
-// The _testcapi extension tests the public C API: header files in Include/ and
-// Include/cpython/ directories. The internal C API must not be tested by
-// _testcapi: use _testinternalcapi for that.
-//
-// _testcapi C files can built with the Py_BUILD_CORE_BUILTIN macro defined if
-// one of the Modules/Setup files asks to build _testcapi as "static"
-// (gh-109723).
-//
-// The Visual Studio projects builds _testcapi with Py_BUILD_CORE_MODULE.
-#undef Py_BUILD_CORE_MODULE
-#undef Py_BUILD_CORE_BUILTIN
+#ifdef PYTESTCAPI_NEED_INTERNAL_API
+#  ifndef Py_BUILD_CORE_BUILTIN
+#    define Py_BUILD_CORE_MODULE 1
+#  endif
+#else
+   // The _testcapi extension tests the public C API: header files in Include/
+   // and Include/cpython/ directories. The internal C API must not be tested
+   // by _testcapi: use _testinternalcapi for that.
+   //
+   // _testcapi C files can built with the Py_BUILD_CORE_BUILTIN macro defined
+   // if one of the Modules/Setup files asks to build _testcapi as "static"
+   // (gh-109723).
+   //
+   // The Visual Studio projects builds _testcapi with Py_BUILD_CORE_MODULE.
+#  undef Py_BUILD_CORE_MODULE
+#  undef Py_BUILD_CORE_BUILTIN
+#endif
 
 #include "Python.h"
 
-#ifdef Py_BUILD_CORE
+#if defined(Py_BUILD_CORE) && !defined(PYTESTCAPI_NEED_INTERNAL_API)
 #  error "_testcapi must test the public Python C API, not the internal C API"
 #endif
 
diff --git a/Modules/_testcapi/vectorcall.c b/Modules/_testcapi/vectorcall.c
index 2b5110f..b30c5e8 100644
--- a/Modules/_testcapi/vectorcall.c
+++ b/Modules/_testcapi/vectorcall.c
@@ -1,3 +1,6 @@
+// clinic/vectorcall.c.h uses internal pycore_modsupport.h API
+#define PYTESTCAPI_NEED_INTERNAL_API
+
 #include "parts.h"
 #include "clinic/vectorcall.c.h"
 
diff --git a/Modules/_testcapi/watchers.c b/Modules/_testcapi/watchers.c
index 8a264bb..a763ff4 100644
--- a/Modules/_testcapi/watchers.c
+++ b/Modules/_testcapi/watchers.c
@@ -1,3 +1,6 @@
+// clinic/watchers.c.h uses internal pycore_modsupport.h API
+#define PYTESTCAPI_NEED_INTERNAL_API
+
 #include "parts.h"
 
 #include "clinic/watchers.c.h"