perf: clear generated primitive arrays with slice deletion

rosidl_generator_py/resource/_msg_support.c.em

@@ -678,25 +678,15 @@ if isinstance(type_, AbstractNestedType):
 @(bi)      Py_DECREF(field);
 @(bi)      return NULL;
 @(bi)    }
-@(bi)    // clear the array, poor approach to remove potential default values
+@(bi)    // clear the array to remove potential default values
 @(bi)    Py_ssize_t length = PyObject_Length(field);
 @(bi)    if (-1 == length) {
 @(bi)      Py_DECREF(field);
 @(bi)      return NULL;
 @(bi)    }
-@(bi)    if (length > 0) {
-@(bi)      PyObject * pop = PyObject_GetAttrString(field, "pop");
-@(bi)      assert(pop != NULL);
-@(bi)      for (Py_ssize_t i = 0; i < length; ++i) {
-@(bi)        PyObject * ret = PyObject_CallFunctionObjArgs(pop, NULL);
-@(bi)        if (!ret) {
-@(bi)          Py_DECREF(pop);
-@(bi)          Py_DECREF(field);
-@(bi)          return NULL;
-@(bi)        }
-@(bi)        Py_DECREF(ret);
-@(bi)      }
-@(bi)      Py_DECREF(pop);
+@(bi)    if (PySequence_DelSlice(field, 0, length) == -1) {
+@(bi)      Py_DECREF(field);
+@(bi)      return NULL;
 @(bi)    }
 @(bi)    if (ros_message->@(member.name).size > 0) {
 @(bi)      // populating the array.array using the frombytes method

rosidl_generator_py/test/test_interfaces.py

@@ -13,8 +13,10 @@
 # limitations under the License.
 
 import array
+import ctypes
 import math
 import sys
+from typing import Any
 
 import numpy
 import pytest
@@ -39,6 +41,48 @@
 from rosidl_parser.definition import UnboundedString
 
 
+_PY_CAPSULE_GET_POINTER = ctypes.pythonapi.PyCapsule_GetPointer
+_PY_CAPSULE_GET_POINTER.argtypes = [ctypes.py_object, ctypes.c_char_p]
+_PY_CAPSULE_GET_POINTER.restype = ctypes.c_void_p
+
+
+def _get_capsule_pointer(capsule: object) -> int:
+    pointer = _PY_CAPSULE_GET_POINTER(capsule, None)
+    assert pointer is not None
+    return pointer
+
+
+def _convert_through_type_support(message_type: Any, message: Any) -> Any:
+    message_type.__import_type_support__()
+    assert message_type._CREATE_ROS_MESSAGE is not None
+    assert message_type._CONVERT_FROM_PY is not None
+    assert message_type._CONVERT_TO_PY is not None
+    assert message_type._DESTROY_ROS_MESSAGE is not None
+
+    create_ros_message_type = ctypes.PYFUNCTYPE(ctypes.c_void_p)
+    convert_from_py_type = ctypes.PYFUNCTYPE(
+        ctypes.c_bool, ctypes.py_object, ctypes.c_void_p)
+    convert_to_py_type = ctypes.PYFUNCTYPE(ctypes.py_object, ctypes.c_void_p)
+    destroy_ros_message_type = ctypes.PYFUNCTYPE(None, ctypes.c_void_p)
+
+    create_ros_message = create_ros_message_type(
+        _get_capsule_pointer(message_type._CREATE_ROS_MESSAGE))
+    convert_from_py = convert_from_py_type(
+        _get_capsule_pointer(message_type._CONVERT_FROM_PY))
+    convert_to_py = convert_to_py_type(
+        _get_capsule_pointer(message_type._CONVERT_TO_PY))
+    destroy_ros_message = destroy_ros_message_type(
+        _get_capsule_pointer(message_type._DESTROY_ROS_MESSAGE))
+
+    ros_message = create_ros_message()
+    assert ros_message is not None
+    try:
+        assert convert_from_py(message, ros_message)
+        return convert_to_py(ros_message)
+    finally:
+        destroy_ros_message(ros_message)
+
+
 def test_basic_types() -> None:
     msg = BasicTypes(check_fields=True)
 
@@ -765,6 +809,33 @@ def test_bounded_sequences() -> None:
     assert msg.bool_values == [True, False]
 
 
+@pytest.mark.parametrize(
+    ('message_type', 'field_name', 'type_code', 'values'),
+    (
+        (BoundedSequences, 'char_values', 'B', [0, 1, 255]),
+        (BoundedSequences, 'float32_values', 'f', [0.0, 1.25, -2.5]),
+        (BoundedSequences, 'int16_values', 'h', [0, -32768, 32767]),
+        (UnboundedSequences, 'uint16_values', 'H', [0, 1, 65535]),
+        (UnboundedSequences, 'int32_values', 'l', [0, -2147483648, 2147483647]),
+        (UnboundedSequences, 'uint64_values', 'Q', [0, 1, 18446744073709551615]),
+    ),
+)
+def test_primitive_sequences_convert_to_py(
+    message_type: Any,
+    field_name: str,
+    type_code: str,
+    values: list[Any],
+) -> None:
+    msg = message_type(check_fields=True)
+    setattr(msg, field_name, values)
+
+    converted_msg = _convert_through_type_support(message_type, msg)
+    converted_field = getattr(converted_msg, field_name)
+
+    assert converted_field.typecode == type_code
+    assert converted_field == array.array(type_code, values)
+
+
 def test_unbounded_sequences() -> None:
     msg = UnboundedSequences(check_fields=True)