👩‍🌾 Export ignition-cmakeN_INCLUDE_DIRS

[chapulina]

While trying to use the macros from #102 on ign-rendering, that library was not being able to find the include ignition/utilities/ExtraTestMacros.hh.

Strangely, ign-gazebo and ign-gui are able to find it fine, see gazebosim/gz-sim#209 and gazebosim/gz-gui#76.

After digging through the CMake variables, I suspect ign-gazebo and ign-gui may be getting the correct include directory from another dependency. My initial guess was ign-tools, because that's a top-level include (IGNITION-TOOLS_INCLUDE_DIRS=/home/chapulina/blueprint_ws/install/include) as opposed to a library-specific include path.

In any case, this PR exposes the standard _INCLUDE_DIRS variable for ign-cmake so it can be used by other projects.

[mxgrey]

Could you point me at the CMakeLists.txt for ign-rendering that links to the ignition-cmake#::utilities target? This sounds like an issue that should be solved in the downstream cmake project, not in this project.

[scpeters]

I suspect ign-gazebo and ign-gui may be getting the correct include directory from another dependency.

Could you point me at the CMakeLists.txt for ign-rendering that links to the ignition-cmake#::utilities target? This sounds like an issue that should be solved in the downstream cmake project, not in this project.

I think ign-gazebo and ign-gui are getting the ignition-cmake#::utilities target from ignition-plugin, which links to it publicly in the core and loader components:

• https://github.com/ignitionrobotics/ign-plugin/blob/master/loader/CMakeLists.txt#L12
• https://github.com/ignitionrobotics/ign-plugin/blob/master/core/CMakeLists.txt#L12

So I agree with @mxgrey that the problem is likely that ign-rendering is not properly linking to ignition-cmake#::utilities when it should be, and we shouldn't need to merge this.

[scpeters]

I think this is a problem in downstream libraries, not in ign-cmake (see earlier comments)

[chapulina]

Ah thank you both. I was just using include_directories on ign-rendering with the new variable:

gazebosim/gz-rendering@ign-rendering2...chapulina/disable_failing

Nice detective work, @scpeters. I searched for an example throughout the libraries and forgot to check ign-plugin. That's what I need!