Issue with compling drake-ros using colcon in Ubuntu 22.04

[phanikiran1169]

Hello,

I am facing issues while building drake_ros (main branch) using colcon

Details

OS: Ubuntu LTS 22.04 LTS
ROS Distribution: Iron
Drake (installed via APT): drake-dev 1.37.0-1

Error Log

Starting >>> drake_ros
Finished <<< drake_ros [28.5s]                       
Starting >>> drake_ros_examples
--- stderr: drake_ros_examples                              
/home/sirhawk/ws_temp/src/drake-ros/drake_ros_examples/examples/multirobot/multirobot.cc: In function ‘int main(int, char**)’:
/home/sirhawk/ws_temp/src/drake-ros/drake_ros_examples/examples/multirobot/multirobot.cc:47:16: error: ‘struct drake::multibody::MultibodyPlantConfig’ has no member named ‘discrete_contact_solver’
   47 |   plant_config.discrete_contact_solver = "sap";
      |                ^~~~~~~~~~~~~~~~~~~~~~~
gmake[2]: *** [examples/multirobot/CMakeFiles/multirobot.dir/build.make:76: examples/multirobot/CMakeFiles/multirobot.dir/multirobot.cc.o] Error 1
gmake[1]: *** [CMakeFiles/Makefile2:258: examples/multirobot/CMakeFiles/multirobot.dir/all] Error 2
gmake[1]: *** Waiting for unfinished jobs....
gmake: *** [Makefile:146: all] Error 2
---
Failed   <<< drake_ros_examples [7.38s, exited with code 2]

Temporary Fix

I have made the following changes in drake-ros/drake_ros_examples/examples/multirobot/multirobot.cc and drake-ros/drake_ros_examples/examples/multirobot/multirobot.py

   // Add a multibody plant and a scene graph to hold the robots
   drake::multibody::MultibodyPlantConfig plant_config;
   plant_config.time_step = 0.001;
-  plant_config.discrete_contact_solver = "sap";
+  // plant_config.discrete_contact_solver = "sap";
   auto [plant, scene_graph] =
       drake::multibody::AddMultibodyPlant(plant_config, &builder);

     # Add a multibody plant and a scene graph to hold the robots
     plant, scene_graph = AddMultibodyPlant(
-        MultibodyPlantConfig(time_step=0.001, discrete_contact_solver="sap"),
+        MultibodyPlantConfig(time_step=0.001),
         builder,
     )

Kindly let me know if the above fix is correct

[IanTheEngineer]

@phanikiran1169, thank you for posting this issue. Your assessment is correct. drake-ros is not yet compatible with Drake version 1.37.0. We'll work to rectify that in #377, but the temporary fix you outlined is a valid solution to allow your workspace to build with the colcon tool. We were using a deprecated flag to designate SAP as the discrete contact solver but that has since become the default solver.