building open_gmapping from source on melodic/ubuntu 18.04

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Edit: update (2019-07-09): it would appear that at least openslam_gmapping has been released into Melodic now by the "ROS Orphaned Package Maintainers" (see here).

That still leaves gmapping itself (ie: the ROS package), so building from source may still be necessary, but it seems that will be done as well (ros-perception/slam_gmapping#72).

Instead of using vanilla upstream, using the latest (Kinetic/Lunar released) patched sources from ros-perception/openslam_gmapping (linked from wiki/openslam_gmapping) built cleanly for me in a ros:melodic Docker container.

Adding ros-perception/slam_gmapping (linked from wiki/slam_gmapping) to that same workspace and building it resulted in a happy catkin_make.

$ docker run -it --rm ros:melodic
(docker) $ apt update
(docker) $ rosdep update
(docker) $ mkdir -p /ros_ws/src
(docker) $ cd /ros_ws
(docker) $ git clone https://github.com/ros-perception/openslam_gmapping src/openslam_gmapping
(docker) $ git clone https://github.com/ros-perception/slam_gmapping src/slam_gmapping
(docker) $ rosdep install --from-paths src/ -i
(docker) $ catkin_make -DCMAKE_BUILD_TYPE=RelWithDebInfo

I've not tested whether it actually all runs, but the fact it still compiles is nice.

After this works, you might also want to take a look at some of the open pull requests against both ros-perception/openslam_gmapping (here) and ros-perception/slam_gmapping (here). They seem to propose a few enhancements and fixes especially for more recent systems and OS.