$ g++-15 --version
g++-15 (Ubuntu 15.2.0-1ubuntu1) 15.2.0

$ cmake .. -GNinja -DCMAKE_CXX_COMPILER=g++-15 -DFLUX_BUILD_MODULE=On
-- The CXX compiler identification is GNU 15.2.0
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/g++-15 - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
CMake Deprecation Warning at build-gcc-modules/_deps/doctest-src/CMakeLists.txt:1 (cmake_minimum_required):
  Compatibility with CMake < 3.10 will be removed from a future version of
  CMake.

  Update the VERSION argument <min> value.  Or, use the <min>...<max> syntax
  to tell CMake that the project requires at least <min> but has been updated
  to work with policies introduced by <max> or earlier.


-- Configuring done (13.5s)
-- Generating done (2.7s)
-- Build files have been written to: /home/ubuntu/Coding/libflux/build-gcc-modules

$ cmake --build . --target test-module-import
[0/2] Re-checking globbed directories...
[5/9] Building CXX object module/CMakeFiles/flux-mod.dir/flux.cpp.o
FAILED: module/CMakeFiles/flux-mod.dir/flux.cpp.o module/CMakeFiles/flux-mod.dir/flux.gcm 
/usr/bin/g++-15  -I/home/ubuntu/Coding/libflux/include -std=c++20 -MD -MT module/CMakeFiles/flux-mod.dir/flux.cpp.o -MF module/CMakeFiles/flux-mod.dir/flux.cpp.o.d -fmodules-ts -fmodule-mapper=module/CMakeFiles/flux-mod.dir/flux.cpp.o.modmap -MD -fdeps-format=p1689r5 -x c++ -o module/CMakeFiles/flux-mod.dir/flux.cpp.o -c /home/ubuntu/Coding/libflux/module/flux.cpp
In file included from /home/ubuntu/Coding/libflux/include/flux/sequence.hpp:20,
                 from /home/ubuntu/Coding/libflux/include/flux.hpp:12,
                 from /home/ubuntu/Coding/libflux/module/flux.cpp:51:
/home/ubuntu/Coding/libflux/include/flux/sequence/unfold.hpp:89:1: internal compiler error: Segmentation fault
   89 | } // namespace flux
      | ^
0x16b39af internal_error(char const*, ...)
	../../src/gcc/diagnostic-global-context.cc:517
0x1093d15 crash_signal
	../../src/gcc/toplev.cc:322
0xf0238c memcpy
	/usr/include/x86_64-linux-gnu/bits/string_fortified.h:29
0xf0238c write
	../../src/gcc/cp/module.cc:2131
0xf030b3 elf_out::end()
	../../src/gcc/cp/module.cc:2258
0x816357 late_finish_module
	../../src/gcc/cp/module.cc:22371
0x816357 fini_modules(cpp_reader*, void*, bool)
	../../src/gcc/cp/module.cc:22413
0x17af1d6 c_parse_final_cleanups()
	../../src/gcc/cp/decl2.cc:5903
0x1cf18e5 c_common_parse_file()
	../../src/gcc/c-family/c-opts.cc:1399
Please submit a full bug report, with preprocessed source (by using -freport-bug).
Please include the complete backtrace with any bug report.
See <file:///usr/share/doc/gcc-15/README.Bugs> for instructions.
ninja: build stopped: subcommand failed.