tl;dr: Enabling quoted string literals in condition attributes in package.xml files.
REP 149 introduced the package manifest format 3 about three years ago.: see the previous thread RFC on REP 149: package format 3 In that format version we introduced a condition attribute with support for a minimal set of expressions.
After using this feature for while we noticed that a particular kind of condition can’t be expressed naturally: if a specific environment variable is or is not empty / not set. To address this use case we want to introduce support for quoted string literals as described in ros-infrastructure/rep#288.
We think this enhancement can be rolled out as an update to the existing REP / format version. That being said if packages start using this new feature they will require an updated parser. An update to the reference implementation is proposed in ros-infrastructure/catkin_pkg#295.
Please provide your feedback on either the REP pull request or if applicable on the catkin_pkg pull request. (Please do not reply in this discourse thread since the audience is very big and not everyone might be interested in the in-depth discussion of this topic.)
Your friendly ROS team