Defect: GCC C extensions used in multiple locations

[rouson]

This issue replaces OpenCoarrays issue 549.

Defect/Bug Report

Observed Behavior

• A struct in libcaf_mpi has a variable length member component that is not the last element in the struct: This causes warnings when compiling with clang because it is a GCC C extension
• ISO_Fortran_binding.h uses variable length arrays (VLAs) inside structs which is a GCC C extension

See also discussion on homebrew pull request 28534.

Expected Behavior

Be able to compile all components written in C because the C code is standards conforming

Steps to Reproduce

compile using clang instead of gcc

Discussion

1. Is there no option other than enumerating every possible rank?
2. Could this be done with a macro?
3. Could we point from within the struct to an external VLA?

[rouson]

@scrasmussen The primary motivation for fixing this issue would be to offer ISO_Fortran_binding to non-GNU compilers, the most likely target for which would be flang because flang uses [clang] as its companion C compiler. However, NVIDIA recently released f18, announced that f18 will replace flang in the future, and f18 has an implementation of ISO_Fortran_binding.h and ISO_Fortran_binding.cc. I think that takes the air out of this issue so I'm closing it. We should discuss other ways to contribute to ISO_Fortran_binding and next steps.

[zbeekman]

I think we have GNU extensions in the core library too, so I’m reopening.

[zbeekman]

Wrong repository... sorry. I'll take this for a test drive with clang.