SchemaExtractor cannot resolve action feedback (pkg/action/X_FeedbackMessage) and service event types

[facontidavide]

Summary

SchemaExtractor only resolves types of the form pkg/msg/Type and always looks for <package share>/msg/<Type>.msg. Types published on action feedback topics (pkg/action/<Action>_FeedbackMessage) and on service introspection event topics (pkg/srv/<Srv>_Event, Jazzy+) have no such file, so get_schema() fails and the topic cannot be subscribed with a schema.

Reproduction (ROS 2 Jazzy)

Any action server, e.g. the tf2_msgs/action/LookupTransform action or a nav2 action, publishes /<action>/_action/feedback with type tf2_msgs/action/LookupTransform_FeedbackMessage (the generated type exists in tf2_msgs/action/detail/lookup_transform__struct.hpp).

SchemaExtractor::try_get_message_definition("tf2_msgs/action/LookupTransform_FeedbackMessage"):

• parse_message_type() (ros2/src/schema_extractor.cpp, ~line 205) keeps only the first segment as package and the last as type name, discarding action.
• build_message_definition_recursive() then reads <share>/tf2_msgs/msg/LookupTransform_FeedbackMessage.msg (ros2/src/schema_extractor.cpp:92), which does not exist. The result is "failed to resolve message definition".

The same happens for pkg/srv/Foo_Event when service introspection is enabled.

Expected

The feedback message is defined by the .action file: X_FeedbackMessage is unique_identifier_msgs/UUID goal_id plus X_Feedback feedback, where X_Feedback is the third section of action/X.action. Service events are defined by the .srv file plus service_msgs/msg/ServiceEventInfo. rosbag2 resolves both in rosbag2_cpp/src/rosbag2_cpp/message_definitions/local_message_definition_source.cpp (see the /action/ and _Event handling around lines 304-346), and it locates interface files through the package's rosidl_interfaces ament resource (ament_index_cpp::get_resource("rosidl_interfaces", pkg, ...)) rather than a fixed path.

Suggested fix

1. Parse the middle segment (msg, srv, action) instead of discarding it.
2. Locate files through the rosidl_interfaces resource index.
3. For action, synthesise X_FeedbackMessage (and X_Goal, X_Result if ever needed) from the .action sections; for srv _Event, synthesise from the .srv sections plus ServiceEventInfo.

A related limitation: types that only ship an .idl (no .msg) are also unresolvable; rosbag2 falls back to the .idl text with encoding ros2idl.

Found while porting SchemaExtractor into another recorder, after comparing it with rosbag2's implementation. Happy to open a PR if the approach above is acceptable.

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Reported with the help of Claude Code.