Fix SetUseSimTime for launch frontends (#488)

1. Fix parsing of action for frontends.
2. Make the Python action handle & normalize substitutions and then
   perform them.

And add frontend tests.

Signed-off-by: Christophe Bedard <[email protected]>

Author: christophebedard

launch_ros/launch_ros/actions/set_use_sim_time.py

@@ -12,12 +12,18 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from typing import List
+from typing import Union
 
 from launch import Action
 from launch.frontend import Entity
 from launch.frontend import expose_action
 from launch.frontend import Parser
 from launch.launch_context import LaunchContext
+from launch.some_substitutions_type import SomeSubstitutionsType
+from launch.substitution import Substitution
+from launch.utilities.type_utils import normalize_typed_substitution
+from launch.utilities.type_utils import perform_typed_substitution
 
 from launch_ros.ros_adapters import get_ros_node
 
@@ -30,32 +36,33 @@ class SetUseSimTime(Action):
 
     def __init__(
         self,
-        value: bool,
+        value: Union[bool, SomeSubstitutionsType],
         **kwargs
     ) -> None:
         """Create a SetUseSimTime action."""
         super().__init__(**kwargs)
-        self.__value = value
+        self.__value = normalize_typed_substitution(value, bool)
 
     @classmethod
     def parse(cls, entity: Entity, parser: Parser):
         """Return `SetUseSimTime` action and kwargs for constructing it."""
         _, kwargs = super().parse(entity, parser)
-        kwargs['value'] = parser.parse_substitution(entity.get_attr('value'))
+        kwargs['value'] = parser.parse_if_substitutions(entity.get_attr('value', data_type=bool))
         return cls, kwargs
 
     @property
-    def value(self) -> bool:
+    def value(self) -> List[Substitution]:
         """Getter for value."""
         return self.__value
 
     def execute(self, context: LaunchContext):
         """Execute the action."""
+        value = perform_typed_substitution(context, self.value, bool)
         node = get_ros_node(context)
         param = Parameter(
             'use_sim_time',
             Parameter.Type.BOOL,
-            self.value
+            value,
         )
         node.set_parameters([param])
         if not node.get_parameter('use_sim_time').get_parameter_value().bool_value:

test_launch_ros/test/test_launch_ros/frontend/test_set_use_sim_timer_frontend.py

@@ -0,0 +1,64 @@
+# Copyright 2025 Open Source Robotics Foundation, Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import io
+import textwrap
+
+from launch import LaunchService
+from launch.frontend import Parser
+from launch.utilities.type_utils import perform_typed_substitution
+from launch_ros.actions import SetUseSimTime
+import pytest
+
+
+yaml_file = textwrap.dedent(
+    r"""
+    launch:
+        - let:
+            name: sim_time
+            value: '1'
+        - set_use_sim_time:
+            value: $(var sim_time)
+    """
+)
+
+
+xml_file = textwrap.dedent(
+    r"""
+    <launch>
+        <let name="sim_time" value="1" />
+        <set_use_sim_time value="$(var sim_time)" />
+    </launch>
+    """
+)
+
+
+@pytest.mark.parametrize(
+    'file',
+    [
+        pytest.param(yaml_file, id='YAML'),
+        pytest.param(xml_file, id='XML'),
+    ],
+)
+def test_set_use_sim_timer(file):
+    root_entity, parser = Parser.load(io.StringIO(file))
+    ld = parser.parse_description(root_entity)
+    ls = LaunchService()
+    ls.include_launch_description(ld)
+    assert 0 == ls.run()
+
+    lc = ls.context
+    assert len(ld.entities) == 2
+    assert isinstance(ld.entities[1], SetUseSimTime)
+    assert perform_typed_substitution(lc, ld.entities[1].value, bool) is True