gh-100637: Fix int and bool __sizeof__ calculation to include the 1 element ob_digit array for 0 and False (#100663)

Fixes behaviour where int (and subtypes like bool) __sizeof__ under-reports true size as it did not take into account the size 1 `ob_digit` array for the zero int.

Co-authored-by: Mark Dickinson <dickinsm@gmail.com>

Lib/test/test_sys.py

@@ -1322,6 +1322,7 @@ class SizeofTest(unittest.TestCase):
         check = self.check_sizeof
         # bool
         check(True, vsize('') + self.longdigit)
+        check(False, vsize('') + self.longdigit)
         # buffer
         # XXX
         # builtin_function_or_method
@@ -1459,7 +1460,7 @@ class SizeofTest(unittest.TestCase):
         # listreverseiterator (list)
         check(reversed([]), size('nP'))
         # int
-        check(0, vsize(''))
+        check(0, vsize('') + self.longdigit)
         check(1, vsize('') + self.longdigit)
         check(-1, vsize('') + self.longdigit)
         PyLong_BASE = 2**sys.int_info.bits_per_digit

Misc/NEWS.d/next/Core and Builtins/2023-01-01-15-59-48.gh-issue-100637.M2n6Kg.rst

@@ -0,0 +1 @@
+Fix :func:`int.__sizeof__` calculation to include the 1 element ob_digit array for 0 and False.

Objects/longobject.c

@@ -5879,7 +5879,10 @@ int___sizeof___impl(PyObject *self)
 {
     Py_ssize_t res;
 
-    res = offsetof(PyLongObject, ob_digit) + Py_ABS(Py_SIZE(self))*sizeof(digit);
+    res = offsetof(PyLongObject, ob_digit)
+        /* using Py_MAX(..., 1) because we always allocate space for at least
+           one digit, even though the integer zero has a Py_SIZE of 0 */
+        + Py_MAX(Py_ABS(Py_SIZE(self)), 1)*sizeof(digit);
     return res;
 }