rosbag2_storage_mcap message definition cache cannot find .msg definitions outside msg dir

[james-rms]

Description

Copying over the description from ros-tooling/rosbag2_storage_mcap#77 :

We were trying to use mcap on a large ROS2 project and ran into an issue where .msg files were not being found in the install/<package_name>/share/<package_name>/msg/*.msg path. We got errors like below and the produced mcap files were empty.

[node-2] [WARN] [1668788082.046164202] [rosbag2_storage_mcap]: no .msg definition for AAA/BBB.msg, falling back to IDL

On closer look we saw that our package is structured to create .msg files in paths like install/<package_name>/share/<package_name>/<sub_directory_name>/*.msg. This is purely for organizational purposes and ROS2 doesn't have issue in finding these. So this PR modifies the MCAP plugin code to look for .msg files in any sub-directory within install/<package_name>/share/<package_name>/. It resolves our problem

Expected Behavior

The MCAP storage plugin finds MSG definitions in any directory that the rest of ROS2 build infrastructure deems acceptable.

Actual Behavior

the MCAP storage plugin fails to find MSG definitions outside of an msg package subdirectory.

To Reproduce

** Steps to reproduce the behavior, e.g.

1. Go to '...'
2. Click on '....'
3. Scroll down to '....'
4. Logs print error '...' **

System (please complete the following information)

• OS: [e.g. Ubuntu Bionic]
• ROS 2 Distro: [e.g. Dashing]
• Version: [release, branch, or commit hash]

Additional context

** Add any other context about the problem here **

[jhurliman]

This should fix the issue, just needs to be ported to this repo: foxglove/ros-foxglove-bridge#95

[aditya2592]

@jhurliman Thanks for making the changes in foxglove-bridge, I copied over and tested the changes to this repo here. Would be great if you could have a look whenever possible!