vtk-m: upstream issues prevent using Xcode clang for +openmp variant

[chrstphrchvz (Christopher Chavez)]

I am creating this ticket mainly to inform the port maintainer and anyone else who is curious. It may not require much (if any) action on MacPorts’ end.

I am interested in compiler.openmp_version allowing use of Xcode clang: ​https://github.com/macports/macports-base/pull/247. To get an idea of what issues a port may run into, I tried vtk-m +openmp as an example (after applying changes proposed in ​https://github.com/macports/macports-ports/pull/13082 and ​https://github.com/macports/macports-ports/pull/13093#issuecomment-976190084).

I believe I have identified a couple of issues in how VTK-m configures with OpenMP support. I would like to report and suggest fixes for them upstream.

1. VTK-m does not use the OpenMP_CXX_INCLUDE_DIRS variable. This causes omp.h to not be found during build, even though the OpenMP_CXX_INCLUDE_DIR variable was specified (as a configure argument -DOpenMP_CXX_INCLUDE_DIR=${prefix}/include/libomp)

2. VTK-m uses the space-separated OpenMP_CXX_FLAGS variable without converting it to a semicolon-separated list before appending it to the desired target property. This causes -Xclang -fopenmp to be treated as a single command line argument rather than two arguments, leading to warnings during build:

   clang: warning: argument unused during compilation: '-Xclang -fopenmp' [-Wunused-command-line-argument]
   

I will attach a brief patch here containing possible fixes for these two issues.

[chrstphrchvz (Christopher Chavez)]

Upstream pull request opened: ​https://gitlab.kitware.com/vtk/vtk-m/-/merge_requests/2637

[chrstphrchvz (Christopher Chavez)]

Replying to chrstphrchvz:

Upstream pull request opened: ​https://gitlab.kitware.com/vtk/vtk-m/-/merge_requests/2637

I have abandoned the pull request. Some alternatives were discussed which seemed better than what I proposed.

I am not intending that this ticket be kept open.