gh-47146: Soft-deprecate structmember.h, expose its contents via Python.h (GH-99014)

The ``structmember.h`` header is deprecated, though it continues to be available
and there are no plans to remove it. There are no deprecation warnings. Old code
can stay unchanged (unless the extra include and non-namespaced macros bother
you greatly). Specifically, no uses in CPython are updated -- that would just be
unnecessary churn.
The ``structmember.h`` header is deprecated, though it continues to be
available and there are no plans to remove it.

Its contents are now available just by including ``Python.h``,
with a ``Py`` prefix added if it was missing:

- `PyMemberDef`, `PyMember_GetOne` and`PyMember_SetOne`
- Type macros like `Py_T_INT`, `Py_T_DOUBLE`, etc.
  (previously ``T_INT``, ``T_DOUBLE``, etc.)
- The flags `Py_READONLY` (previously ``READONLY``) and
  `Py_AUDIT_READ` (previously all uppercase)

Several items are not exposed from ``Python.h``:

- `T_OBJECT` (use `Py_T_OBJECT_EX`)
- `T_NONE` (previously undocumented, and pretty quirky)
- The macro ``WRITE_RESTRICTED`` which does nothing.
- The macros ``RESTRICTED`` and ``READ_RESTRICTED``, equivalents of
  `Py_AUDIT_READ`.
- In some configurations, ``<stddef.h>`` is not included from ``Python.h``.
  It should be included manually when using ``offsetof()``.

The deprecated header continues to provide its original
contents under the original names.
Your old code can stay unchanged, unless the extra include and non-namespaced
macros bother you greatly.

There is discussion on the issue to rename `T_PYSSIZET` to `PY_T_SSIZE` or
similar. I chose not to do that -- users will probably copy/paste that with any
spelling, and not renaming it makes migration docs simpler.


Co-Authored-By: Alexander Belopolsky <abalkin@users.noreply.github.com>
Co-Authored-By: Matthias Braun <MatzeB@users.noreply.github.com>

1 files changed, 4 insertions, 147 deletions

diff --git a/Modules/_testcapimodule.c b/Modules/_testcapimodule.c
index 9dd09f6..83eef73 100644
--- a/Modules/_testcapimodule.c
+++ b/Modules/_testcapimodule.c
@@ -21,7 +21,7 @@
 
 #include "Python.h"
 #include "marshal.h"              // PyMarshal_WriteLongToFile
-#include "structmember.h"         // PyMemberDef
+#include "structmember.h"         // for offsetof(), T_OBJECT
 #include <float.h>                // FLT_MAX
 #include <signal.h>
 
@@ -3371,147 +3371,6 @@ static PyMethodDef TestMethods[] = {
     {NULL, NULL} /* sentinel */
 };
 
-typedef struct {
-    char bool_member;
-    char byte_member;
-    unsigned char ubyte_member;
-    short short_member;
-    unsigned short ushort_member;
-    int int_member;
-    unsigned int uint_member;
-    long long_member;
-    unsigned long ulong_member;
-    Py_ssize_t pyssizet_member;
-    float float_member;
-    double double_member;
-    char inplace_member[6];
-    long long longlong_member;
-    unsigned long long ulonglong_member;
-} all_structmembers;
-
-typedef struct {
-    PyObject_HEAD
-    all_structmembers structmembers;
-} test_structmembers;
-
-static struct PyMemberDef test_members[] = {
-    {"T_BOOL", T_BOOL, offsetof(test_structmembers, structmembers.bool_member), 0, NULL},
-    {"T_BYTE", T_BYTE, offsetof(test_structmembers, structmembers.byte_member), 0, NULL},
-    {"T_UBYTE", T_UBYTE, offsetof(test_structmembers, structmembers.ubyte_member), 0, NULL},
-    {"T_SHORT", T_SHORT, offsetof(test_structmembers, structmembers.short_member), 0, NULL},
-    {"T_USHORT", T_USHORT, offsetof(test_structmembers, structmembers.ushort_member), 0, NULL},
-    {"T_INT", T_INT, offsetof(test_structmembers, structmembers.int_member), 0, NULL},
-    {"T_UINT", T_UINT, offsetof(test_structmembers, structmembers.uint_member), 0, NULL},
-    {"T_LONG", T_LONG, offsetof(test_structmembers, structmembers.long_member), 0, NULL},
-    {"T_ULONG", T_ULONG, offsetof(test_structmembers, structmembers.ulong_member), 0, NULL},
-    {"T_PYSSIZET", T_PYSSIZET, offsetof(test_structmembers, structmembers.pyssizet_member), 0, NULL},
-    {"T_FLOAT", T_FLOAT, offsetof(test_structmembers, structmembers.float_member), 0, NULL},
-    {"T_DOUBLE", T_DOUBLE, offsetof(test_structmembers, structmembers.double_member), 0, NULL},
-    {"T_STRING_INPLACE", T_STRING_INPLACE, offsetof(test_structmembers, structmembers.inplace_member), 0, NULL},
-    {"T_LONGLONG", T_LONGLONG, offsetof(test_structmembers, structmembers.longlong_member), 0, NULL},
-    {"T_ULONGLONG", T_ULONGLONG, offsetof(test_structmembers, structmembers.ulonglong_member), 0, NULL},
-    {NULL}
-};
-
-
-static PyObject *
-test_structmembers_new(PyTypeObject *type, PyObject *args, PyObject *kwargs)
-{
-    static char *keywords[] = {
-        "T_BOOL", "T_BYTE", "T_UBYTE", "T_SHORT", "T_USHORT",
-        "T_INT", "T_UINT", "T_LONG", "T_ULONG", "T_PYSSIZET",
-        "T_FLOAT", "T_DOUBLE", "T_STRING_INPLACE",
-        "T_LONGLONG", "T_ULONGLONG",
-        NULL};
-    static const char fmt[] = "|bbBhHiIlknfds#LK";
-    test_structmembers *ob;
-    const char *s = NULL;
-    Py_ssize_t string_len = 0;
-    ob = PyObject_New(test_structmembers, type);
-    if (ob == NULL)
-        return NULL;
-    memset(&ob->structmembers, 0, sizeof(all_structmembers));
-    if (!PyArg_ParseTupleAndKeywords(args, kwargs, fmt, keywords,
-                                     &ob->structmembers.bool_member,
-                                     &ob->structmembers.byte_member,
-                                     &ob->structmembers.ubyte_member,
-                                     &ob->structmembers.short_member,
-                                     &ob->structmembers.ushort_member,
-                                     &ob->structmembers.int_member,
-                                     &ob->structmembers.uint_member,
-                                     &ob->structmembers.long_member,
-                                     &ob->structmembers.ulong_member,
-                                     &ob->structmembers.pyssizet_member,
-                                     &ob->structmembers.float_member,
-                                     &ob->structmembers.double_member,
-                                     &s, &string_len
-                                     , &ob->structmembers.longlong_member,
-                                     &ob->structmembers.ulonglong_member
-        )) {
-        Py_DECREF(ob);
-        return NULL;
-    }
-    if (s != NULL) {
-        if (string_len > 5) {
-            Py_DECREF(ob);
-            PyErr_SetString(PyExc_ValueError, "string too long");
-            return NULL;
-        }
-        strcpy(ob->structmembers.inplace_member, s);
-    }
-    else {
-        strcpy(ob->structmembers.inplace_member, "");
-    }
-    return (PyObject *)ob;
-}
-
-static void
-test_structmembers_free(PyObject *ob)
-{
-    PyObject_Free(ob);
-}
-
-static PyTypeObject test_structmembersType = {
-    PyVarObject_HEAD_INIT(NULL, 0)
-    "test_structmembersType",
-    sizeof(test_structmembers),         /* tp_basicsize */
-    0,                                  /* tp_itemsize */
-    test_structmembers_free,            /* destructor tp_dealloc */
-    0,                                  /* tp_vectorcall_offset */
-    0,                                  /* tp_getattr */
-    0,                                  /* tp_setattr */
-    0,                                  /* tp_as_async */
-    0,                                  /* tp_repr */
-    0,                                  /* tp_as_number */
-    0,                                  /* tp_as_sequence */
-    0,                                  /* tp_as_mapping */
-    0,                                  /* tp_hash */
-    0,                                  /* tp_call */
-    0,                                  /* tp_str */
-    PyObject_GenericGetAttr,            /* tp_getattro */
-    PyObject_GenericSetAttr,            /* tp_setattro */
-    0,                                  /* tp_as_buffer */
-    0,                                  /* tp_flags */
-    "Type containing all structmember types",
-    0,                                  /* traverseproc tp_traverse */
-    0,                                  /* tp_clear */
-    0,                                  /* tp_richcompare */
-    0,                                  /* tp_weaklistoffset */
-    0,                                  /* tp_iter */
-    0,                                  /* tp_iternext */
-    0,                                  /* tp_methods */
-    test_members,                       /* tp_members */
-    0,
-    0,
-    0,
-    0,
-    0,
-    0,
-    0,
-    0,
-    test_structmembers_new,             /* tp_new */
-};
-
 
 typedef struct {
     PyObject_HEAD
@@ -4064,11 +3923,6 @@ PyInit__testcapi(void)
 
     Py_SET_TYPE(&_HashInheritanceTester_Type, &PyType_Type);
 
-    Py_SET_TYPE(&test_structmembersType, &PyType_Type);
-    Py_INCREF(&test_structmembersType);
-    /* don't use a name starting with "test", since we don't want
-       test_capi to automatically call this */
-    PyModule_AddObject(m, "_test_structmembersType", (PyObject *)&test_structmembersType);
     if (PyType_Ready(&matmulType) < 0)
         return NULL;
     Py_INCREF(&matmulType);
@@ -4197,6 +4051,9 @@ PyInit__testcapi(void)
     if (_PyTestCapi_Init_Float(m) < 0) {
         return NULL;
     }
+    if (_PyTestCapi_Init_Structmember(m) < 0) {
+        return NULL;
+    }
 
 #ifndef LIMITED_API_AVAILABLE
     PyModule_AddObjectRef(m, "LIMITED_API_AVAILABLE", Py_False);