Remove plugin interface and support custom sensors

[chapulina]

Requires gazebosim/gz-plugin#35

This does a lot of the same things as #38, except for:

• I got rid of the IGN_SENSORS_REGISTER_SENSOR in favor of using IGNITION_ADD_PLUGIN directly. That matches better what we've been doing on other libraries and simplifies some registration details. The downside is that it isn't being tick-tocked yet. But I wonder if this was even usable by downstream users, considering Support custom sensors #9. What do you think, @iche033 ?
• I didn't need to change any tests or anything in the Manager
• There's no assumption that the interface we want is the last one, we iterate until finding the correct interface.

I only tested this locally, curious to see how it will work on CI.

---

6 months later...

This PR now depends on gazebosim/sdformat#652

This pull request started as a migration from Ignition Common plugins to Ignition Plugins. As we iterated on it, it became clear that it wasn't feasible to link against the sensor plugins, and then load them at runtime one more time, which is what the old implementation was doing.

We can't escape linking against each sensor if we want to use their APIs in Gazebo systems. But we can live without the plugin interface. With that in mind, we decided to completely remove the plugin interface instead of migrating it to Ignition Plugin.

See the migration guide for more information on what has changed, and the new examples for how to use the current APIs, including an example of how to implement custom sensors.

---

Let me know what you think, @ahcorde

[ahcorde]

Did you try to run any test on ign-gazebo ? or Did you try to run ign gazebo with some sensor plugins?

All sensor plugins are failing

	 47 - INTEGRATION_air_pressure_system (Failed)
	 49 - INTEGRATION_altimeter_system (SEGFAULT)
	 67 - INTEGRATION_diff_drive_system (Failed)
	 81 - INTEGRATION_imu_system (SEGFAULT)
	 99 - INTEGRATION_logical_camera_system (SEGFAULT)
	103 - INTEGRATION_magnetometer_system (SEGFAULT)
	127 - INTEGRATION_sdf_include (Failed)
	139 - INTEGRATION_log_system (Failed)
	141 - INTEGRATION_wheel_slip (Failed)
	147 - INTEGRATION_camera_video_record_system (SEGFAULT)
	149 - INTEGRATION_depth_camera (SEGFAULT)
	151 - INTEGRATION_gpu_lidar (SEGFAULT)
	153 - INTEGRATION_rgbd_camera (SEGFAULT)
	155 - INTEGRATION_sensors_system (SEGFAULT)

When I run for example ign gazebo -r -v 4 camera_sensor.sdf I got this error:

[Err] [SensorFactory.cc:119] Unable to instantiate sensor plugin for [ignition-sensors4-camera]
[Err] [Sensors.cc:516] Failed to create sensor [camera::link::camera]
[Err] [SceneManager.cc:993] Unable to find sensor []
[Err] [RenderUtil.cc:503] Failed to create sensor []

This is the issue why I think we should use GLOBAL instead of LOCAL.

[chapulina]

Did you try to run any test on ign-gazebo ?

Argh, no I hadn't, and now I see it doesn't work. It was too good to be true. I'll look into it more.

I'm having a hard time trying out #38 because it's outdated, so I'm pulling changes from it. I tried fixing conflicts but I must have done something wrong because it wasn't working for me 😕

[ahcorde]

I will update my PR

[chapulina]

I opened this for review.

• All tests pass locally using Accept null dlhandle and support custom dlopen flags gz-plugin#35
• ign-gazebo's tests pass locally and sensors work at runtime using Upgrade ign-sensors and support custom sensors gz-sim#617 (be sure to update to the latest main branch on ign-rendering)
• This approach lets anyone implement custom sensors that aren't installed with ign-sensors, see Support custom sensors #100

[ahcorde]

Style issues https://github.com/ignitionrobotics/ign-sensors/pull/90/checks?check_run_id=3265904621

[ahcorde]

ups still some style issues https://github.com/ignitionrobotics/ign-sensors/pull/90/checks?check_run_id=3293527185

[codecov]

Codecov Report

Merging #90 (949f519) into main (d21c6f3) will increase coverage by 0.28%.
The diff coverage is 56.84%.

@@            Coverage Diff             @@
##             main      #90      +/-   ##
==========================================
+ Coverage   77.22%   77.51%   +0.28%     
==========================================
  Files          23       24       +1     
  Lines        2358     2326      -32     
==========================================
- Hits         1821     1803      -18     
+ Misses        537      523      -14     

Impacted Files	Coverage Δ
src/AirPressureSensor.cc	85.50% <ø> (-0.21%)	⬇️
src/AltimeterSensor.cc	87.95% <ø> (-0.15%)	⬇️
src/CameraSensor.cc	76.49% <ø> (+1.77%)	⬆️
src/DepthCameraSensor.cc	73.83% <ø> (-0.11%)	⬇️
src/GpuLidarSensor.cc	88.15% <ø> (-0.08%)	⬇️
src/ImuSensor.cc	90.09% <ø> (-0.10%)	⬇️
src/Lidar.cc	72.19% <ø> (-0.15%)	⬇️
src/LogicalCameraSensor.cc	89.55% <ø> (-0.16%)	⬇️
src/MagnetometerSensor.cc	88.09% <ø> (-0.15%)	⬇️
src/SensorFactory.cc	25.00% <0.00%> (-29.44%)	⬇️
... and 8 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update d21c6f3...949f519. Read the comment docs.

Style issues are resolved and CI is all happy

[chapulina]

As mentioned on the migration guide, it wasn't possible to tick-tock all of the API. So once this is merged, downstream (i.e. ign-gazebo) will be broken. So here are the next steps:

• Someone other than me needs to approve Upgrade ign-sensors and support custom sensors gz-sim#617
• We merge this PR
• Trigger nightlies in the middle of the day so we have them quickly: https://build.osrfoundation.org/job/ign-sensors6-debbuilder/
• Once nightlies are in, rerun CI for the ign-gazebo PR
• Merge that after CI comes back ok