Hi,

adios2 fails to build in a test rebuild on at least amd64 and arm64 with
gcc-16/g++-16, but builds properly with gcc-15/g++-15. The severity of this
report will be raised before the forky release.

The full build log can be found at:
https://people.debian.org/~ema/gcc-16-rebuilds/output-1/adios2_arm64.build.xz

The last lines of the build log are at the end of this report.

To build with GCC 16, either set CC=gcc-16 CXX=g++-16 explicitly,
or install the gcc, g++, gfortran, ... packages from experimental.

  apt-get -t=experimental install g++

Common build failures include unused (but set) variables, array subscripts
partly outside array bounds, and new/dropped symbols in Debian symbols files.
For other C/C++ related build failures see the porting guide at
http://gcc.gnu.org/gcc-16/porting_to.html

Please only close this issue after double-checking that the package can be
built correctly.

Please do not reassign this bug to another package. If a fix in another package
is required, then file a bug for the other package (or clone), and mark this
bug as blocked by the bug in the other package.

[...]

This is not a bug in adios2.  The error message states that it's
coming from openmpi (mpifort).

I don't think this is a bug in openmpi either.  It's just looking for
the fortran it was compiled against.  Other compilers can be used
instead through the FC environment variable. Perhaps it's an openmpi
bug that it's looking for the specific gfortran version by default,
rather than using the general /usr/bin/gfortran.

So the build error in adios2 will clear once openmpi is rebuilt
against gcc 16 (or reconfigured to use default gfortran).

This is not a bug in adios2 as such. adios2 is simply using mpifort
from openmpi-bin.

mpifort has some issues with hardcoding the gfortran version,
cf. Bug#1133595