Treat IGN_LAUNCH_CONFIG_PATH as a path list.

[peci1]

Bug Report

Fixes issue #92.

Summary

Treat IGN_LAUNCH_CONFIG_PATH as a path list instead of just one path.

Depends on ign-common C bindings: gazebosim/gz-common#168 , because I felt reinventing the C++ wheel in Ruby is not really the way to go.

This is my first piece of code in Ruby, so give it a thorough check because I generally didn't know what I'm doing :) Most importantly, it'd be fine to find a way to use the Importer in such a way that importing the second library doesn't break the code loaded from the first one, but I couldn't wrap my head around it...

I was also thinking whether it's better to pass an absolute path to the ign-common library or just a filename, and decided just for the filename to ease having multiple ign-common versions side-by-side and choosing between them based on LD_LIBRARY_PATH. But passing the absolute path is possible if you'd think it's better for some reason.

I also didn't know how to add tests for this feature. However, there were none for the whole Ruby command file anyways...

I do the development on Dome, though it seemed to me this feature could go even in Citadel, so I pointed this PR to the Citadel version and maintain a 1-1 cherry-pick of it for Dome in https://github.com/peci1/ign-launch/tree/env-pathlist . That might speed up forward-porting of the feature, which I'm interested in :)

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• codecheck passed (See
  contributing)
• All tests passed (See
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[peci1]

After a discussion in gazebosim/gz-common#168 I changed this PR to not use the C API of ign-common SystemPaths and instead implemented a simple path split mechanism in Ruby.

I tested locally on Linux all possible combinations of launch files - a default-installed one, launch file from first workspace, launchfile from an overlay workspace, absolute path. In all cases, ign launch behaves as expected both with 1-element and 2-element path lists.

[peci1]

To say it explicitly - this PR no longer depends on gazebosim/gz-common#168 .

[chapulina]

Thanks for iterating and thanks for the documentation!