Don't crash when type definition cannot be found

[emersonknapp]

Fail gracefully to an empty type definition, if the name of the type was not fully understood by the local message definition source file search.

This is a fix to the crashing aspect of #1336 and #1286, which will downgrade the issue to "incomplete information in bag", which we have decided is a better outcome than a crash.

[MichaelOrlov]

LGTM.

[emersonknapp]

Gist: https://gist.githubusercontent.com/emersonknapp/0765b85b4298c80c570196adb92faa35/raw/cb4ebfa636908f3e5e1d6d4ad8f5a5d3d1c135da/ros2.repos
BUILD args: --packages-above-and-dependencies rosbag2_cpp
TEST args: --packages-above rosbag2_cpp
ROS Distro: rolling
Job: ci_launcher
ci_launcher ran: https://ci.ros2.org/job/ci_launcher/12117

• Linux
• Linux-aarch64
• Windows

[emersonknapp]

@Mergifyio backport iron

[mergify]

backport iron

✅ Backports have been created

• #1352 Don't crash when type definition cannot be found (backport #1350) has been created for branch iron

[russkel]

Given that humble is going to be around for a while as LTS, should this also be backported?

[emersonknapp]

@russkel Good instincts! It would be a yes, except the feature set LocalMessageDefinitionSource that finds message definitions to add to bagfiles doesn't exist yet in Humble, so it doesn't have that crash case.

[russkel]

@russkel Good instincts! It would be a yes, except the feature set LocalMessageDefinitionSource that finds message definitions to add to bagfiles doesn't exist yet in Humble, so it doesn't have that crash case.

How unfortunate. Presumably that's not a trivial merge then?

[emersonknapp]

Typically significant API changes (and therefore large new features) are very hard to backport, mostly we'll only do minor feature extensions and bugfixes.

I did just remember while looking at it, that Humble does have the MessageDefinitionCache, but it was part of the rosbag2_storage_mcap plugin (it was later moved into the rosbag2_cpp core where it can pass defintions to any storage implementation). That being the case, I do believe that Humble actually does have this crash case for MCAP users, so I can do a manual backport of the equivalent fix.

[ros-discourse]

This pull request has been mentioned on ROS Discourse. There might be relevant details there:

https://discourse.ros.org/t/ros-2-tsc-meeting-minutes-2023-06-15/32038/1