Adding check for standalone project.

[pshriwise]

This PR adds a check to determine if mcnp2cad is being built as standalone or as part of another project (the DAGMC-Trelis plugin). This should fix the problem we're seeing with having to run make and cmake more than once when building the importer.

[gonuke]

Hmmm... surprised that this was necessary....

[gonuke]

doesn't it find the library when being built as part of the plugin?

[pshriwise]

Not if it hasn't been built yet. find_library wants a pre-existing library. Skipping this step allows the dependencies in DAGMC-Trelis (or another external package) to set the build order correctly.

[gonuke]

What if, instead, we tweaked the DAGMC-Trelis CMakeLists.txt file to add_subdirectory(mcnp2cad) after the the iGeom is build?

[pshriwise]

I looked into that, but most of the solutions were fairly complicated and fragile, being outside of CMake's intended use of add_subdirectory.

One other solution I looked at was the externalproject_add Cmake command, which would get, configure, and build mcnp2cad. It can also make this process dependent on other targets in the main project. Maybe that's the way to go for a DAGMC-Trelis side solution?

https://cmake.org/cmake/help/v3.0/module/ExternalProject.html

[gonuke]

If line 82 is moved to line 140 in the plugin's CMakeList.txt file, won't this ensure that iGeom has been built?

[pshriwise]

Sadly no. CMake is going to traverse all subdirectories and configure them before building any of the targets. (I did try this to make sure though.)

[gonuke]

boo! OK - but don't we eventually need to find_library when we build as part of the plugin, as well?

[pshriwise]

We build the iGeom target/library in the plugin so CMake knows right where it is, thankfully :)

[gonuke]

yeah... OK - work for us now, but if someone else wants to connect mcnp2cad they'll have to be careful to do the same...
Thanks @pshriwise