Exporting plugins to nav2. How to?

edit

I want to write a custom local planner and a custom recovery. I have made an ament_cmake package, written the code in .cpp files with .h files next to them. It compiles fine. Here's the setup.

./src/prepare_for_path.h
./src/prepare_for_path.cpp
./src/rpp_controller.h
./src/rpp_controller.cpp
./CMakeLists.txt
./package.xml
./plugins.xml

rpp_controller.h:

...
namespace plugins
{
class RPPController : public nav2_core::Controller
...

rpp_controller.cpp:

...
#include "pluginlib/class_list_macros.hpp"
PLUGINLIB_EXPORT_CLASS(plugins::RPPController, nav2_core::Controller)

prepare_for_path.h:

...
namespace plugins 
{
class PrepareForPath : public nav2_recoveries::Recovery<SomeRecoveryType>
...

prepare_for_path.cpp:

...
#include "pluginlib/class_list_macros.hpp"
PLUGINLIB_EXPORT_CLASS(plugins::PrepareForPath, nav2_core::Recovery)

plugins.xml:

<class_libraries>
    <library path="prepare_for_path">
        <class name="plugins/PrepareForPath" type="plugins::PrepareForPath" base_class_type="nav2_core::Recovery">
            <description>This prepares the robot to run a path.</description>
        </class>
    </library>
    <library path="rpp_controller">
        <class name="plugins/RPPController" type="plugins::RPPController" base_class_type="nav2_core::Controller">
            <description>Regulated pure pursuit controller </description>
        </class>
    </library>
</class_libraries>

CMakeLists.txt: (select bits)

set(controller_name rpp_controller)
set(prepare_name prepare_for_path)

add_library(${controller_name} SHARED src/${controller_name}.cpp)
add_library(${prepare_name} SHARED src/${prepare_name}.cpp)

ament_target_dependencies(${controller_name} ${controller_deps})
ament_target_dependencies(${prepare_name} ${prepare_deps})

pluginlib_export_plugin_description_file(nav2_core plugins.xml)

install(TARGETS ${controller_name} ${prepare_name}
  ARCHIVE DESTINATION lib
  LIBRARY DESTINATION lib
  RUNTIME DESTINATION bin
)

install(FILES plugins.xml
  DESTINATION share/{PROJECT_NAME}
)

ament_export_libraries(
  ${controller_name}
  ${prepare_name}
)

ament_package()

Unsure what to write in package.xml, it seems to make no difference so I'm excluding it for brevity. Tell me if this is incorrect.

Meanwhile, launching the nav2 stack with some recovery params:

recoveries_server:
  ros__parameters:
    ...
    recovery_plugins: [..., "prepare"]
    prepare:
      plugin: "plugins/PrepareForPath"

Controller params:

controller_server:
  ros__parameters:
    ...
    controller_plugins: ["FollowPath"]
    FollowPath:
      plugin: plugins/RPPController

Launch output:

...
[controller_server-1]: Created controller : FollowPath of type plugins/RPPController
[controller_server-1]: Controller Server has FollowPath  controllers available.
...
[recoveries_server-3]: Creating recovery plugin prepare of type plugins/PrepareForPath
[recoveries_server-3]: Failed to create recovery prepare of type plugins/PrepareForPath. Exception: Failed to load library /hugo_ws/install/plugins/lib/libprepare_for_path.so. Make sure that you are calling the PLUGINLIB_EXPORT_CLASS macro in the library code, and that names are consistent between this macro and your XML. Error string: Could not load library LoadLibrary error: /hugo_ws/install/plugins/lib/libprepare_for_path.so: undefined symbol: _ZTVN13plugins14PrepareForPathE, at /opt/ros/foxy/src/rcutils/src/shared_library.c:84

And then, it crashes. Now, for some questions. How come the local planner is exported correctly, while the recovery is not? They look identically treated to me.

Pluginlib is extremely opaque to me - how can I view what plugins are available? In general, how do I go about troubleshooting something like this?

I have been following tutorials but I can't ever be sure about which major version these are working with. I reverted back to comparing to the github repo, which should work, but even that doesn't work.