uninformative crash and error message for invalid parameter override

[christianrauch]

Bug report

Setting an invalid parameter override crashes the process and gives an uninformative error message.

Required Info:

• Operating System: Ubuntu 22.04
• Installation type: binaries
• Version or commit hash: 5.3.1
• DDS implementation: default
• Client library (if applicable): rcl

Steps to reproduce issue

1. sudo apt install ros-humble-demo-nodes-cpp
2. ros2 run demo_nodes_cpp talker --ros-args -p bla

Expected behavior

An error message or warning informing about the missing value assignment should be shown. I.e. the message should say that -p bla is not a valid parameter override, but -p bla:=5 is.

Even better, the parameter bla should be set to uninitialised (ParameterType::PARAMETER_NOT_SET).

Actual behavior

Crash with:

[ERROR] [1660855233.229710370] [rcl]: Failed to parse global arguments
terminate called after throwing an instance of 'rclcpp::exceptions::RCLInvalidROSArgsError'
  what():  failed to initialize rcl: Couldn't parse parameter override rule: '-p bla'. Error: Expected lexeme type (22) not found, search ended at index 3, at ./src/rcl/lexer_lookahead.c:239, at ./src/rcl/arguments.c:343
[ros2run]: Aborted

[fujitatomoya]

I think that this is because application does not catch the exception from rclcpp::init (rcl_init)

# ros2 run demo_nodes_cpp add_two_ints_client 1 2 --ros-args -p bla
[ERROR] [1660931840.357026857] [rcl]: Failed to parse global arguments
terminate called after throwing an instance of 'rclcpp::exceptions::RCLInvalidROSArgsError'
  what():  failed to initialize rcl: Couldn't parse parameter override rule: '-p bla'. Error: Expected lexeme type (22) not found, search ended at index 3, at /root/ros2_ws/colcon_ws/src/ros2/rcl/rcl/src/rcl/lexer_lookahead.c:239, at /root/ros2_ws/colcon_ws/src/ros2/rcl/rcl/src/rcl/arguments.c:343
[ros2run]: Aborted

this can be with following patch,

diff --git a/demo_nodes_cpp/src/services/add_two_ints_client.cpp b/demo_nodes_cpp/src/services/add_two_ints_client.cpp
index 8442801..b0cdf0d 100644
--- a/demo_nodes_cpp/src/services/add_two_ints_client.cpp
+++ b/demo_nodes_cpp/src/services/add_two_ints_client.cpp
@@ -43,7 +43,12 @@ int main(int argc, char ** argv)
   // Force flush of the stdout buffer.
   setvbuf(stdout, NULL, _IONBF, BUFSIZ);
 
-  rclcpp::init(argc, argv);
+  try {
+    rclcpp::init(argc, argv);
+  } catch (const std::exception & exception) {
+    RCLCPP_ERROR(rclcpp::get_logger("rclcpp"), exception.what());
+    return EXIT_FAILURE;
+  }
 
   auto node = rclcpp::Node::make_shared("add_two_ints_client");

# ros2 run demo_nodes_cpp add_two_ints_client 1 2 --ros-args -p bla
[ERROR] [1660931652.776928271] [rcl]: Failed to parse global arguments
[ERROR] [1660931652.776993285] [rclcpp]: failed to initialize rcl: Couldn't parse parameter override rule: '-p bla'. Error: Expected lexeme type (22) not found, search ended at index 3, at /root/ros2_ws/colcon_ws/src/ros2/rcl/rcl/src/rcl/lexer_lookahead.c:239, at /root/ros2_ws/colcon_ws/src/ros2/rcl/rcl/src/rcl/arguments.c:343
[ros2run]: Process exited with failure 1

[clalancette]

[rclcpp]: failed to initialize rcl: Couldn't parse parameter override rule: '-p bla'. Error: Expected lexeme type (22) not found, search ended at index 3, at /root/ros2_ws/colcon_ws/src/ros2/rcl/rcl/src/rcl/lexer_lookahead.c:239, at /root/ros2_ws/colcon_ws/src/ros2/rcl/rcl/src/rcl/arguments.c:343

I still think this error message isn't as useful as it could be. It's exposing a low-level detail (the lexer parse error), rather than the higher-level "you provided an parameter argument that is missing :=", which is arguably more useful to the end-user.