Message generation bombs for multiple package versions

[stonier]

Problem: If there's a deb installed version of a package and a source installed version, it will sometimes pull the older version.

Reason: message generation's StringFileProvider stores information in a google concurrentmap (hashmap) which provides no guarantees about ordering. When generating sources, it will then ignore the second message file found in that map...A comment from MessageDefinitionFileProvider:

// First definition wins.

[stonier]

Need something that will read catkin package information...I used to have some java code lying around that did this.

Probably easiest place to insert it is where that comment is.

[stonier]

Easier solution, just narrow the scope of the package path to the package with the newer version. The catkin-gradle plugin is already close to getting that data, just feed that to the message generator.

Longer term, it would be good if message generation parsed over a catkin package database, which could additionally check for message generation dependencies instead of making assumptions such as everything is in 'msg' subfolders.