[Foxy backport] Improve error message for malformed YAML files

[s-hillerk]

Bug report

Passing a malformed YAML parameter file crashes nodes without hinting at the cause. The symptoms are the same as #553:

free(): double free detected in tcache 2
Aborted (core dumped)

Required Info:

• Operating System:
  • Ubuntu 20.04
• Installation type:
  • ROS2 deb repo via apt
• Version or commit hash:
  • ros-foxy-rcl 1.1.7-1focal.20200921.18150
• DDS implementation:
  • default
• Client library (if applicable):
  • (rclpy)

Steps to reproduce issue

echo malformed::: > /tmp/settings.yaml
ros2 run <any node> --ros-args --params-file /tmp/settings.yaml

Expected behavior

The user is informed that the YAML file is malformed.

Actual behavior

The program crashes. The user is puzzled and is not told the cause of the crash.

[clalancette]

I think this is essentially a request to backport #556 to Foxy (since I confirmed that it is fixed on the latest). I'll add this to the Foxy board for a backport.

[clalancette]

Help doing this would be appreciated.

[jacobperron]

With the latest release 1.1.8, we don't see a double free error, but instead:

[ERROR] [1602279724.674172361] [rcl]: Failed to parse global arguments

>>> [rcutils|error_handling.c:108] rcutils_set_error_state()
This error state is being overwritten:

  'Couldn't parse params file: '--params-file /tmp/settings.yaml'. Error: Cannot have a value before ros__parameters at line 1, at /tmp/binarydeb/ros-foxy-rcl-yaml-param-parser-1.1.8/src/parse.c:623, at /tmp/binarydeb/ros-foxy-rcl-1.1.8/src/rcl/arguments.c:391'

with this new error message:

  'context is zero-initialized, at /tmp/binarydeb/ros-foxy-rcl-1.1.8/src/rcl/context.c:51'

rcutils_reset_error() should be called after error handling to avoid this.
<<<
[ERROR] [1602279724.674250769] [rclcpp]: failed to finalize context: context is zero-initialized, at /tmp/binarydeb/ros-foxy-rcl-1.1.8/src/rcl/context.c:51
terminate called after throwing an instance of 'rclcpp::exceptions::RCLInvalidROSArgsError'
  what():  failed to initialize rcl: error not set

Which has a better error message, though we could probably improve things so that we avoid overwriting the error state.

[jacobperron]

I'm going to close this since it looks like the error message has been improved since the latest release for Foxy.