gh-128863: Deprecate _PyLong_FromDigits() function (#127939)

Author: skirpichev

Doc/deprecations/c-api-pending-removal-in-3.18.rst

@@ -7,7 +7,8 @@ Pending removal in Python 3.18
   * :c:func:`!_PyDict_GetItemStringWithError`: use :c:func:`PyDict_GetItemStringRef`.
   * :c:func:`!_PyDict_Pop()`: :c:func:`PyDict_Pop`.
   * :c:func:`!_PyLong_Sign()`: use :c:func:`PyLong_GetSign`.
-  * :c:func:`!_PyLong_New`: use :c:func:`PyLongWriter_Create`.
+  * :c:func:`!_PyLong_FromDigits` and :c:func:`!_PyLong_New`:
+    use :c:func:`PyLongWriter_Create`.
   * :c:func:`!_PyThreadState_UncheckedGet`: use :c:func:`PyThreadState_GetUnchecked`.
   * :c:func:`!_PyUnicode_AsString`: use :c:func:`PyUnicode_AsUTF8`.
   * :c:func:`!_Py_HashPointer`: use :c:func:`Py_HashPointer`.

Doc/whatsnew/3.14.rst

@@ -1396,7 +1396,8 @@ Deprecated
   * :c:func:`!_PyDict_GetItemStringWithError`: use :c:func:`PyDict_GetItemStringRef`.
   * :c:func:`!_PyDict_Pop()`: use :c:func:`PyDict_Pop`.
   * :c:func:`!_PyLong_Sign()`: use :c:func:`PyLong_GetSign`.
-  * :c:func:`!_PyLong_New`: use :c:func:`PyLongWriter_Create`.
+  * :c:func:`!_PyLong_FromDigits` and :c:func:`!_PyLong_New`:
+    use :c:func:`PyLongWriter_Create`.
   * :c:func:`!_PyThreadState_UncheckedGet`: use :c:func:`PyThreadState_GetUnchecked`.
   * :c:func:`!_PyUnicode_AsString`: use :c:func:`PyUnicode_AsUTF8`.
   * :c:func:`!_Py_HashPointer`: use :c:func:`Py_HashPointer`.

Include/cpython/longintrepr.h

@@ -105,7 +105,7 @@ Py_DEPRECATED(3.14) PyAPI_FUNC(PyLongObject*) _PyLong_New(Py_ssize_t);
 // Return a copy of src.
 PyAPI_FUNC(PyObject*) _PyLong_Copy(PyLongObject *src);
 
-PyAPI_FUNC(PyLongObject*) _PyLong_FromDigits(
+Py_DEPRECATED(3.14) PyAPI_FUNC(PyLongObject*) _PyLong_FromDigits(
     int negative,
     Py_ssize_t digit_count,
     digit *digits);

Misc/NEWS.d/next/C_API/2025-01-15-11-42-07.gh-issue-128863.C9MkB_.rst

@@ -5,7 +5,8 @@ Python 3.18:
 * :c:func:`!_PyDict_GetItemStringWithError`: use :c:func:`PyDict_GetItemStringRef`.
 * :c:func:`!_PyDict_Pop()`: use :c:func:`PyDict_Pop`.
 * :c:func:`!_PyLong_Sign()`: use :c:func:`PyLong_GetSign`.
-* :c:func:`!_PyLong_New`: use :c:func:`PyLongWriter_Create`.
+* :c:func:`!_PyLong_FromDigits` and :c:func:`!_PyLong_New`:
+  use :c:func:`PyLongWriter_Create`.
 * :c:func:`!_PyThreadState_UncheckedGet`: use :c:func:`PyThreadState_GetUnchecked`.
 * :c:func:`!_PyUnicode_AsString`: use :c:func:`PyUnicode_AsUTF8`.
 * :c:func:`!_Py_HashPointer`: use :c:func:`Py_HashPointer`.

Objects/longobject.c

@@ -205,7 +205,6 @@ _PyLong_FromDigits(int negative, Py_ssize_t digit_count, digit *digits)
     }
     PyLongObject *result = long_alloc(digit_count);
     if (result == NULL) {
-        PyErr_NoMemory();
         return NULL;
     }
     _PyLong_SetSignAndDigitCount(result, negative?-1:1, digit_count);
@@ -217,15 +216,29 @@ PyObject *
 _PyLong_Copy(PyLongObject *src)
 {
     assert(src != NULL);
+    int sign;
 
     if (_PyLong_IsCompact(src)) {
         stwodigits ival = medium_value(src);
         if (IS_SMALL_INT(ival)) {
             return get_small_int((sdigit)ival);
         }
+        sign = _PyLong_CompactSign(src);
+    }
+    else {
+        sign = _PyLong_NonCompactSign(src);
     }
+
     Py_ssize_t size = _PyLong_DigitCount(src);
-    return (PyObject *)_PyLong_FromDigits(_PyLong_IsNegative(src), size, src->long_value.ob_digit);
+    PyLongObject *result = long_alloc(size);
+
+    if (result == NULL) {
+        return NULL;
+    }
+    _PyLong_SetSignAndDigitCount(result, sign, size);
+    memcpy(result->long_value.ob_digit, src->long_value.ob_digit,
+           size * sizeof(digit));
+    return (PyObject *)result;
 }
 
 static PyObject *