Feature ci new ubuntu

[holke]

Describe your changes here:

Update the CI to use Ubuntu 22.04.
This step is necessary to prepare for using the VTK library in the CI, since VTK 9.1 is only available from Ubuntu 22.04.

Needed to fix some new compiler warnings.

Unfortunately one warning cannot be fixed, since it is concerned with MPI usage and know by the MPI community.
Disabling the warning only temporarily did not work, so now the compiler option causing this warning (-Wstringop-overflow) is disabled for all CI runs.

All these boxes must be checked by the reviewers before merging the pull request:

• The author added a BSD statement to doc/ (or already has one)

• The code compiles without warning in debugging and release mode, with and without MPI (this should be executed automatically in a github action)

  If the Pull request indroduces code that is not covered by the github action (for example coupling with a new library):

  • Should this use case be added to the github action?
  • If not, does the specific use case compile and all tests pass (check manually)

• All tests pass (in various configurations, this should be executed automatically in a github action)

• New source/header files are properly added to the Makefiles

• The reviewer executed the new code features at least once and checked the results manually

• The code is covered in an existing or new test case

• The code follows the t8code coding guidelines

• The code is well documented

• All function declarations, structs/classes and their members have a proper doxygen documentation

• All new algorithms and data structures are sufficiently optimal in terms of memory and runtime (If this should be merged, but there is still potential for optimization, create a new issue)

• Testing of this template: If you feel something is missing from this list, contact the developers

[holke]

The problem is an unsolvable issue with autotools library finding and newer C++ compilers.
It occurs when we build with CC=g++
We cannot fix this at the moment.

Proposed solution, that i will try: Only use Ubuntu 22.04. for the VTK runs and use older versions for the other runs.

[sandro-elsweijer]

The problem is an unsolvable issue with autotools library finding and newer C++ compilers. It occurs when we build with CC=g++ We cannot fix this at the moment.

Proposed solution, that i will try: Only use Ubuntu 22.04. for the VTK runs and use older versions for the other runs.

Does this mean, that t8code is not able to run on Ubuntu 22.04 with autotools in general?

[holke]

The problem is an unsolvable issue with autotools library finding and newer C++ compilers. It occurs when we build with CC=g++ We cannot fix this at the moment.
Proposed solution, that i will try: Only use Ubuntu 22.04. for the VTK runs and use older versions for the other runs.

Does this mean, that t8code is not able to run on Ubuntu 22.04 with autotools in general?

No, t8code will (and does) run on Ubuntu 22.04.
Only the configuration CC=g++ CXX=g++ (or CC=mpicxx ...) does fail.
This configuration is covered in several ways in our test cases and is somewhat important.
However, i do not see it as that critical, since most use cases would just use the C compiler.

[holke]

For the record, here is a link to the discussion on the autotools mailing list.
https://www.mail-archive.com/bug-autoconf@gnu.org/msg04294.html

When using AC_SEARCH_LIB (or similar), autotools builds a test program in the configure script to detect the library.
From gcc v8 on, the C++ compiler throws an error on the test script (instead of a warning as before).
This causes the configure script to fail in finding the library and thus abort.

We have to wait for an update of autotools to fix this.

[holke]

I close this now since we cannot solve the autotools issue.

[holke]

Added this to the known issues Wik page https://github.com/holke/t8code/wiki/Known-issues