gh-122943: Rework support of var-positional parameter in Argument Cli…

…nic (GH-122945)

Move creation of a tuple for var-positional parameter out of
_PyArg_UnpackKeywordsWithVararg().
Merge _PyArg_UnpackKeywordsWithVararg() with _PyArg_UnpackKeywords().
Add a new parameter in _PyArg_UnpackKeywords().

The "parameters" and "converters" attributes of ParseArgsCodeGen no
longer contain the var-positional parameter. It is now available as the
"varpos" attribute. Optimize code generation for var-positional
parameter and reuse the same generating code for functions with and without
keyword parameters.

Add special converters for var-positional parameter. "tuple" represents it as
a Python tuple and "array" represents it as a continuous array of PyObject*.
"object" is a temporary alias of "tuple".

Include/internal/pycore_modsupport.h

@@ -76,7 +76,7 @@ PyAPI_FUNC(int) _PyArg_ParseStackAndKeywords(
     ...);
 
 // Export for 'math' shared extension
-PyAPI_FUNC(PyObject * const *) _PyArg_UnpackKeywords(
+PyAPI_FUNC(PyObject * const *) _PyArg_UnpackKeywordsEx(
     PyObject *const *args,
     Py_ssize_t nargs,
     PyObject *kwargs,
@@ -85,20 +85,19 @@ PyAPI_FUNC(PyObject * const *) _PyArg_UnpackKeywords(
     int minpos,
     int maxpos,
     int minkw,
+    int varpos,
     PyObject **buf);
 #define _PyArg_UnpackKeywords(args, nargs, kwargs, kwnames, parser, minpos, maxpos, minkw, buf) \
     (((minkw) == 0 && (kwargs) == NULL && (kwnames) == NULL && \
-      (minpos) <= (nargs) && (nargs) <= (maxpos) && (args) != NULL) ? (args) : \
-     _PyArg_UnpackKeywords((args), (nargs), (kwargs), (kwnames), (parser), \
-                           (minpos), (maxpos), (minkw), (buf)))
-
-// Export for '_testclinic' shared extension
-PyAPI_FUNC(PyObject * const *) _PyArg_UnpackKeywordsWithVararg(
-        PyObject *const *args, Py_ssize_t nargs,
-        PyObject *kwargs, PyObject *kwnames,
-        struct _PyArg_Parser *parser,
-        int minpos, int maxpos, int minkw,
-        int vararg, PyObject **buf);
+      (minpos) <= (nargs) && (nargs) <= (maxpos) && (args) != NULL) ? \
+      (args) : \
+     _PyArg_UnpackKeywordsEx((args), (nargs), (kwargs), (kwnames), (parser), \
+                           (minpos), (maxpos), (minkw), 0, (buf)))
+#define _PyArg_UnpackKeywordsWithVararg(args, nargs, kwargs, kwnames, parser, minpos, maxpos, minkw, buf) \
+    (((minkw) == 0 && (kwargs) == NULL && (kwnames) == NULL && \
+      (minpos) <= (nargs) && (args) != NULL) ? (args) : \
+     _PyArg_UnpackKeywordsEx((args), (nargs), (kwargs), (kwnames), (parser), \
+                           (minpos), (maxpos), (minkw), 1, (buf)))
 
 #ifdef __cplusplus
 }

Include/internal/pycore_tuple.h

@@ -20,7 +20,7 @@ extern PyStatus _PyTuple_InitGlobalObjects(PyInterpreterState *);
 
 #define _PyTuple_ITEMS(op) _Py_RVALUE(_PyTuple_CAST(op)->ob_item)
 
-extern PyObject *_PyTuple_FromArray(PyObject *const *, Py_ssize_t);
+PyAPI_FUNC(PyObject *)_PyTuple_FromArray(PyObject *const *, Py_ssize_t);
 PyAPI_FUNC(PyObject *)_PyTuple_FromStackRefSteal(const union _PyStackRef *, Py_ssize_t);
 PyAPI_FUNC(PyObject *)_PyTuple_FromArraySteal(PyObject *const *, Py_ssize_t);