Fix resizing to 0 length / clearing leaving one byte alloc

Author: cmaloney

Lib/test/test_bytes.py

@@ -1394,10 +1394,11 @@ def test_clear(self):
         b = bytearray(b'abc')
         b.clear()
         self.assertEqual(b.__alloc__(), 0)
-        self.assertEqual(sys.getsizeof(b), 0)
+        base_size = sys.getsizeof(bytearray())
+        self.assertEqual(sys.getsizeof(b), base_size)
         c = b.copy()
         self.assertEqual(c.__alloc__(), 0)
-        self.assertEqual(sys.getsizeof(c), 0)
+        self.assertEqual(sys.getsizeof(c), base_size)
 
     def test_copy(self):
         b = bytearray(b'abc')
@@ -1466,7 +1467,8 @@ def test_take_bytes(self):
         self.assertEqual(len(ba), 0)
         self.assertEqual(ba, bytearray(b''))
         self.assertEqual(ba.__alloc__(), 0)
-        self.assertEqual(sys.getsizeof(ba), 0)
+        base_size = sys.getsizeof(bytearray())
+        self.assertEqual(sys.getsizeof(ba), base_size)
 
         # Positive and negative slicing.
         ba = bytearray(b'abcdef')

Objects/bytearrayobject.c

@@ -223,6 +223,11 @@ bytearray_resize_lock_held(PyObject *self, Py_ssize_t requested_size)
         if (size < alloc / 2) {
             /* Major downsize; resize down to exact size */
             alloc = size + 1;
+
+            /* If new size is 0; don't need to allocate one byte for null. */
+            if (size == 0) {
+                alloc = 0;
+            }
         }
         else {
             /* Minor downsize; quick exit */
@@ -238,7 +243,7 @@ bytearray_resize_lock_held(PyObject *self, Py_ssize_t requested_size)
             alloc = size + (size >> 3) + (size < 9 ? 3 : 6);
         }
         else {
-            /* Major upsize; resize up to exact size */
+            /* Major upsize; resize up to exact size. Upsize always means size > 0 */
             alloc = size + 1;
         }
     }