comm_env_push_compute_comm Subroutine

   subroutine comm_env_push_compute_comm(comm)
      !! TEST/TOOLING-ONLY.  Temporarily overrides what
      !! `comm_env_compute_comm()` returns to `comm`, until the matching
      !! `comm_env_pop_compute_comm()`.
      !!
      !! Exists so a test can run a genuinely serial "reference" engine
      !! (`compute_size=1`) on EVERY physical rank while still calling a
      !! COLLECTIVE report (`ocean_console_stats_report`, which always
      !! reduces over `comm_env_compute_comm()`, the real job
      !! communicator): pushing a per-rank self-communicator around that
      !! one call makes the collective an identity op on each rank's own
      !! copy instead of allreducing `nprocs` independent serial replicas
      !! into one bogus sum.  See
      !! `tests/mpi/test_ocean_decomp_bitid_mpi.F90`'s
      !! `check_periodic_sponge_serial_out` for the call site and
      !! `run_one`'s HAZARD comment for the full story.
      !!
      !! NOT for production code paths — it exists purely to let a test
      !! stand up an alternate communicator around a fixed call without
      !! threading a `comm` argument through every intermediate routine.
      !! One-level only: a push while an override is already active is a
      !! bug in the caller (a missing pop, or an attempt to nest) and
      !! fails loud rather than silently discarding or stacking past
      !! `COMPUTE_COMM_OVERRIDE_MAX_DEPTH`.
      type(comm_t), intent(in) :: comm
      if (compute_comm_override_depth >= COMPUTE_COMM_OVERRIDE_MAX_DEPTH) then
         error stop "comm_env_push_compute_comm: override already active "// &
            "(one-level stack) -- call comm_env_pop_compute_comm first"
      end if
      compute_comm_override = comm
      compute_comm_override_depth = compute_comm_override_depth + 1
   end subroutine comm_env_push_compute_comm