Fix MOM6SOLO build in the EMC branch.

[aerorahul]

There is an issue with compiling the standalone MOM6 within UFS (or even without UFS) in the dev/emc branch

There was a bug in the way the wave forcing subroutine was being called with incorrect number of arguments.

To reproduce the compilation error from the UFS-weather-model repo

CMAKE_FLAGS="-DMOM6SOLO=ON -DS2S=ON -DDATM=ON" BUILD_VERBOSE=1 BUILD_JOBS=1 BUILD_DIR=build-datmmom6 ./build.sh

[ 99%] Building Fortran object MOM6-interface/CMakeFiles/mom6solo.dir/MOM6/config_src/solo_driver/MOM_driver.F90.o
cd /Users/rmahajan/scratch/UFSwork/weather-develop/build-datmmom6/MOM6-interface && /opt/modules/gnu-9.3.0/mpich/3.3.1/bin/mpifort -DENABLE_QUAD_PRECISION -DGFS_PHYS -DINTERNAL_FILE_NML -Duse_libMPI -Duse_netCDF -I/Users/rmahajan/scratch/UFSwork/weather-develop/build-datmmom6/MOM6-interface/mod -I/Users/rmahajan/scratch/UFSwork/weather-develop/build-datmmom6/MOM6-interface/mod_solo -I/Users/rmahajan/scratch/UFSwork/weather-develop/MOM6-interface/MOM6/config_src/dynamic -I/Users/rmahajan/scratch/UFSwork/weather-develop/MOM6-interface/MOM6/src/framework -I/Users/rmahajan/scratch/UFSwork/weather-develop/FMS/include -I/Users/rmahajan/scratch/UFSwork/weather-develop/FMS/fms -I/Users/rmahajan/scratch/UFSwork/weather-develop/FMS/mpp/include -I/Users/rmahajan/scratch/UFSwork/weather-develop/build-datmmom6/FMS/mod -I/opt/modules/gnu-9.3.0/mpich-3.3.1/netcdf/4.7.4/include -g -fbacktrace -fdefault-real-8 -fdefault-double-8 -Waliasing -fcray-pointer -fconvert=big-endian -ffree-line-length-none -fno-range-check -fbacktrace -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX11.0.sdk -mmacosx-version-min=10.15 -Jmod_solo -c /Users/rmahajan/scratch/UFSwork/weather-develop/MOM6-interface/MOM6/config_src/solo_driver/MOM_driver.F90 -o CMakeFiles/mom6solo.dir/MOM6/config_src/solo_driver/MOM_driver.F90.o
/Users/rmahajan/scratch/UFSwork/weather-develop/MOM6-interface/MOM6/config_src/solo_driver/MOM_driver.F90:491:79:

  491 |       call Update_Surface_Waves(grid, GV, US, time, time_step_ocean, waves_csp)
      |                                                                               1
Error: Missing actual argument for argument 'forces' at (1)
make[2]: *** [MOM6-interface/CMakeFiles/mom6solo.dir/MOM6/config_src/solo_driver/MOM_driver.F90.o] Error 1
make[1]: *** [MOM6-interface/CMakeFiles/mom6solo.dir/all] Error 2
make: *** [all] Error 2

[aerorahul]

Please assign to the appropriate person.

[aerorahul]

This is all that is required to enable building of mom6solo at this time.

~/s/U/w/M/MOM6 ❯❯❯ git diff                                       feature/update-to-GFDL-20201022 ✱
diff --git i/src/user/MOM_wave_interface.F90 w/src/user/MOM_wave_interface.F90
index e9b0669f4..b2ca9c875 100644
--- i/src/user/MOM_wave_interface.F90
+++ w/src/user/MOM_wave_interface.F90
@@ -452,7 +452,7 @@ subroutine Update_Surface_Waves(G, GV, US, Day, dt, CS, forces)
   type(unit_scale_type),   intent(in)  :: US   !< A dimensional unit scaling type
   type(time_type),         intent(in)  :: Day !< Current model time
   type(time_type),         intent(in)  :: dt  !< Timestep as a time-type
-  type(mech_forcing),      intent(in)  :: forces !< MOM_forcing_type
+  type(mech_forcing),      intent(in), optional  :: forces !< MOM_forcing_type
   ! Local variables
   integer :: ii, jj, kk, b
   type(time_type) :: Day_Center

But the issue should be resolved more carefully and systematically by working with someone from GFDL. dev/emc should not maintain its own version of the following files that reside in src, else we would be cherry-picking every single time there is a rebase/merge from main

src/core/MOM_forcing_type.F90
src/user/MOM_wave_interface.F90

[jiandewang]

besides what you pointed, there are also some codes need to be cleaned in GFDL's driver code. I fully agree with you that we need to solve this in a careful way as we don't want to break GFDL side system. At the time when Brandon and Jessica merged in the wave section of code in EMC repo, they didn't test in the stand along mode (and they couldn't as the stand alone feature was not in the system yet at that time).

[aerorahul]

Ok. Good. Please start with identifying those codes that need to be cleaned, create issues and assign them.
The longer this stays diverged, the more difficult it will be to reconcile later.
There are other groups developing ocean wave interaction with MOM6.