Build issue with flang 21

[opoplawski]

There is an attempt to rebuild the stripy conda package with flang 21 here: conda-forge/stripy-feedstock#25

It's failing with errors like:

  [34/39] Linking target _stripack.cp310-win_amd64.pyd
  FAILED: [code=1104] _stripack.cp310-win_amd64.pyd
  "link"  /MACHINE:x64 /OUT:_stripack.cp310-win_amd64.pyd _stripack.cp310-win_amd64.pyd.p/meson-generated_..__stripackmodule.c.obj _stripack.cp310-win_amd64.pyd.p/meson-generated_..__stripack-f2pywrappers.f.obj _stripack.cp310-win_amd64.pyd.p/src_stripack.f90.obj _stripack.cp310-win_amd64.pyd.p/D__bld_stripy_1763207111809__h_env_lib_site-packages_numpy_f2py_src_fortranobject.c.obj "/release" "/nologo" "/OPT:REF" "/DLL" "/IMPLIB:_stripack.cp310-win_amd64.lib" "-static" "-Wl,-defaultlib:D:/bld/stripy_1763207111809/_build_env/lib/clang/21/lib/windows/clang_rt.builtins-x86_64.lib" "D:\bld\stripy_1763207111809\_h_env\libs\python310.lib" "kernel32.lib" "user32.lib" "gdi32.lib" "winspool.lib" "shell32.lib" "ole32.lib" "oleaut32.lib" "uuid.lib" "comdlg32.lib" "advapi32.lib"
  LINK : warning LNK4044: unrecognized option '/static'; ignored
  LINK : warning LNK4044: unrecognized option '/Wl,-defaultlib:D:/bld/stripy_1763207111809/_build_env/lib/clang/21/lib/windows/clang_rt.builtins-x86_64.lib'; ignored
  LINK : fatal error LNK1104: cannot open file 'flang_rt.runtime.dynamic.lib'
  [35/39] Linking target _tripack.cp310-win_amd64.pyd
  FAILED: [code=1104] _tripack.cp310-win_amd64.pyd
  "link"  /MACHINE:x64 /OUT:_tripack.cp310-win_amd64.pyd _tripack.cp310-win_amd64.pyd.p/meson-generated_..__tripackmodule.c.obj _tripack.cp310-win_amd64.pyd.p/meson-generated_..__tripack-f2pywrappers.f.obj _tripack.cp310-win_amd64.pyd.p/src_tripack.f90.obj _tripack.cp310-win_amd64.pyd.p/D__bld_stripy_1763207111809__h_env_lib_site-packages_numpy_f2py_src_fortranobject.c.obj "/release" "/nologo" "/OPT:REF" "/DLL" "/IMPLIB:_tripack.cp310-win_amd64.lib" "-static" "-Wl,-defaultlib:D:/bld/stripy_1763207111809/_build_env/lib/clang/21/lib/windows/clang_rt.builtins-x86_64.lib" "D:\bld\stripy_1763207111809\_h_env\libs\python310.lib" "kernel32.lib" "user32.lib" "gdi32.lib" "winspool.lib" "shell32.lib" "ole32.lib" "oleaut32.lib" "uuid.lib" "comdlg32.lib" "advapi32.lib"
  LINK : warning LNK4044: unrecognized option '/static'; ignored
  LINK : warning LNK4044: unrecognized option '/Wl,-defaultlib:D:/bld/stripy_1763207111809/_build_env/lib/clang/21/lib/windows/clang_rt.builtins-x86_64.lib'; ignored
  LINK : fatal error LNK1104: cannot open file 'flang_rt.runtime.dynamic.lib'
  [36/39] Compiling Fortran object _ssrfpack.cp310-win_amd64.pyd.p/src_ssrfpack.f.obj
  flang: warning: argument unused during compilation: '-Wall' [-Wunused-command-line-argument]
  ninja: build stopped: subcommand failed.
  error: subprocess-exited-with-error

Any idea what might be going on here? Thanks.

[brmather]

Thanks for the report. I've pushed a change on branch numpy2-build-robustness (031477f) that makes meson.build only emit the GNU/gfortran-specific link flags when the Fortran compiler actually is gfortran:

if meson.get_compiler('fortran').get_id() == 'gcc'
  # -static (Windows/MinGW) or -Wl,-rpath,... (Unix)
endif

That removes stripy's contribution to the noise in your log — the LNK4044: unrecognized option '/static'; ignored warning came from our unconditional -static, which is a MinGW convention that MSVC's link doesn't understand. (get_compiler('fortran') returns the host compiler, so gfortran cross-builds like conda-forge linux-aarch64/osx-arm64 still get the right flags.)

However, I don't think this fully fixes your build. The fatal error in that log is separate from stripy:

LINK : fatal error LNK1104: cannot open file 'flang_rt.runtime.dynamic.lib'

That's flang 21's runtime library (the flang runtime was renamed to flang_rt around LLVM 20/21), and the -Wl,-defaultlib:...clang_rt.builtins... line is injected by the flang driver itself, not by stripy. So the remaining failure looks like a flang-21 / compiler-activation packaging issue on the feedstock side rather than something in stripy's build. Worth checking whether flang_rt is being provided/linked correctly in conda-forge/stripy-feedstock#25.

If you can retry PR #25 against this branch, it'd confirm whether removing our -static clears the warnings and isolates the flang_rt problem.