Fix bytearray_resize_storage()

Rename bytearray_realign_data_lock_held() to
bytearray_resize_storage().

On error, only move data if ob_start was different than ob_bytes.

Add one more test: resize() shrinks without logical offset.

Author: vstinner

Lib/test/test_bytes.py

@@ -1573,28 +1573,30 @@ def test_resize_error(self):
         # gh-157242: If bytearray.resize() fails (memory allocation failure),
         # the bytearray must be left unchanged.
 
-        # Simple bytearray
-        data = b'some data'
-        ba = bytearray(data)
-        with inject_memory_error(self, 0):
-            ba.resize(1024)
-        self.assertEqual(ba, bytearray(data))
-
-        # growing bytearray with non-zero logical start
-        ba = bytearray(b'0123456789')
-        expected = ba[3:]
-        del ba[:3]
-        with inject_memory_error(self, 0):
-            ba.resize(1024)
-        self.assertEqual(ba, expected)
-
-        # shrink bytearray with non-zero logical start
-        ba = bytearray(b'0123456789')
-        expected = ba[3:]
-        del ba[:3]
-        with inject_memory_error(self, 0):
-            ba.resize(1)
-        self.assertEqual(ba, expected)
+        offset = 3
+        for logical_offset in (False, True):
+            with self.subTest(logical_offset=logical_offset):
+                # grow bytearray
+                ba = bytearray(b'0123456789')
+                if logical_offset:
+                    expected = ba[offset:]
+                    del ba[:offset]
+                else:
+                    expected = ba.copy()
+                with inject_memory_error(self, 0):
+                    ba.resize(1024)
+                self.assertEqual(ba, expected)
+
+                # shrink bytearray
+                ba = bytearray(b'0123456789')
+                if logical_offset:
+                    expected = ba[offset:]
+                    del ba[:offset]
+                else:
+                    expected = ba.copy()
+                with inject_memory_error(self, 0):
+                    ba.resize(1)
+                self.assertEqual(ba, expected)
 
     def test_take_bytes(self):
         ba = bytearray(b'ab')

Objects/bytearrayobject.c

@@ -225,8 +225,8 @@ PyByteArray_AsString(PyObject *self)
 
 
 static int
-bytearray_realign_data_lock_held(PyByteArrayObject *self,
-                                 Py_ssize_t new_size, Py_ssize_t alloc)
+bytearray_resize_storage(PyByteArrayObject *self,
+                         Py_ssize_t new_size, Py_ssize_t alloc)
 {
     _Py_CRITICAL_SECTION_ASSERT_OBJECT_LOCKED(self);
     assert(1 <= new_size && new_size <= alloc);
@@ -247,7 +247,7 @@ bytearray_realign_data_lock_held(PyByteArrayObject *self,
     }
 
     if (_PyBytes_ResizeKeepOnError(&self->ob_bytes_object, alloc) < 0) {
-        if (new_size < size) {
+        if (old_start != self->ob_bytes && new_size < size) {
             // Move remaining bytes
             Py_ssize_t moved = new_size;
             Py_ssize_t remaining = size - moved;
@@ -330,8 +330,7 @@ bytearray_resize_lock_held(PyObject *self, Py_ssize_t requested_size)
         return -1;
     }
 
-    if (bytearray_realign_data_lock_held(obj, requested_size,
-                                         (Py_ssize_t)alloc) < 0) {
+    if (bytearray_resize_storage(obj, requested_size, (Py_ssize_t)alloc) < 0) {
         return -1;
     }
 
@@ -1670,7 +1669,7 @@ bytearray_take_bytes_impl(PyByteArrayObject *self, PyObject *n)
     memcpy(PyBytes_AS_STRING(remaining), self->ob_start + to_take,
            remaining_length);
 
-    if (bytearray_realign_data_lock_held(self, to_take, to_take) < 0) {
+    if (bytearray_resize_storage(self, to_take, to_take) < 0) {
         Py_DECREF(remaining);
         return NULL;
     }