FMS2: Safe inspection of unlimited dim name

The FMS2 function `get_unlimited_dimension_name` raises a netCDF error
if no unlimited dimension is found.  This is problematic for legacy or
externally created input files which may have not identifed their time
axis as unlimited.

This patch adds a new function, `find_unlimited_dimension_name` which
mirrors the FMS2 function but returns an empty string if none are found.

This is an internal function, not intended for use outside of the
module.

config_src/infra/FMS2/MOM_io_infra.F90

@@ -17,6 +17,7 @@ module MOM_io_infra
 use fms2_io_mod,          only : variable_att_exists, get_variable_attribute, get_variable_num_dimensions
 use fms2_io_mod,          only : get_variable_dimension_names, is_dimension_registered, get_dimension_size
 use fms2_io_mod,          only : is_dimension_unlimited, register_axis, unlimited
+use fms2_io_mod,          only : get_dimension_names
 use fms2_io_mod,          only : get_global_io_domain_indices
 use fms_io_utils_mod,     only : fms2_file_exist => file_exists
 use fms_io_utils_mod,     only : get_filename_appendix
@@ -335,7 +336,7 @@ subroutine open_file(IO_handle, filename, action, MOM_domain, threading, fileset
   if ((file_mode == APPEND_FILE) .and. file_exists(filename_tmp, MOM_Domain)) then
     ! Determine the latest file time and number of records so far.
     success = fms2_open_file(fileObj_read, trim(filename_tmp), "read", MOM_domain%mpp_domain)
-    call get_unlimited_dimension_name(fileObj_read, dim_unlim_name)
+    dim_unlim_name = find_unlimited_dimension_name(fileObj_read)
     if (len_trim(dim_unlim_name) > 0) &
       call get_dimension_size(fileObj_read, trim(dim_unlim_name), IO_handle%num_times)
     if (IO_handle%num_times > 0) &
@@ -477,7 +478,7 @@ subroutine get_file_info(IO_handle, ndim, nvar, ntime)
   if (present(nvar)) nvar = get_num_variables(IO_handle%fileobj)
   if (present(ntime)) then
     ntime = 0
-    call get_unlimited_dimension_name(IO_handle%fileobj, dim_unlim_name)
+    dim_unlim_name = find_unlimited_dimension_name(IO_handle%fileobj)
     if (len_trim(dim_unlim_name) > 0) &
       call get_dimension_size(IO_handle%fileobj, trim(dim_unlim_name), ntime)
   endif
@@ -500,8 +501,9 @@ subroutine get_file_times(IO_handle, time_values, ntime)
   if (present(ntime)) ntime = ntimes
   if (ntimes > 0) then
     allocate(time_values(ntimes))
-    call get_unlimited_dimension_name(IO_handle%fileobj, dim_unlim_name)
-    call fms2_read_data(IO_handle%fileobj, trim(dim_unlim_name), time_values)
+    dim_unlim_name = find_unlimited_dimension_name(IO_handle%fileobj)
+    if (len_trim(dim_unlim_name) > 0) &
+      call fms2_read_data(IO_handle%fileobj, trim(dim_unlim_name), time_values)
   endif
 end subroutine get_file_times
 
@@ -1747,9 +1749,10 @@ integer function write_time_if_later(IO_handle, field_time)
   if ((field_time > IO_handle%file_time) .or. (IO_handle%num_times == 0)) then
     IO_handle%file_time = field_time
     IO_handle%num_times = IO_handle%num_times + 1
-    call get_unlimited_dimension_name(IO_handle%fileobj, dim_unlim_name)
-    call write_data(IO_handle%fileobj, trim(dim_unlim_name), (/field_time/), &
-                    corner=(/IO_handle%num_times/), edge_lengths=(/1/))
+    dim_unlim_name = find_unlimited_dimension_name(IO_handle%fileobj)
+    if (len_trim(dim_unlim_name) > 0) &
+      call write_data(IO_handle%fileobj, trim(dim_unlim_name), [field_time], &
+                      corner=[IO_handle%num_times], edge_lengths=[1])
   endif
 
   write_time_if_later = IO_handle%num_times
@@ -1935,4 +1938,34 @@ subroutine write_metadata_global(IO_handle, name, attribute)
   call register_global_attribute(IO_handle%fileobj, name, attribute, len_trim(attribute))
 end subroutine write_metadata_global
 
+!> Return unlimited dimension name in file, or empty string if none exists.
+function find_unlimited_dimension_name(fileobj) result(label)
+  type(FmsNetcdfDomainFile_t), intent(in) :: fileobj
+    !< File handle
+  character(len=:), allocatable :: label
+    !< Unlimited dimension name, or empty string if none exists
+
+  integer :: ndims
+    !< Number of dimensions
+  character(len=256), allocatable :: dim_names(:)
+    !< File handle dimension names
+  integer :: i
+    !< Loop index
+
+  ndims = get_num_dimensions(fileobj)
+  allocate(dim_names(ndims))
+  call get_dimension_names(fileobj, dim_names)
+
+  do i = 1, ndims
+    if (is_dimension_unlimited(fileobj, dim_names(i))) then
+      label = trim(dim_names(i))
+      exit
+    endif
+  enddo
+  deallocate(dim_names)
+
+  if (.not. allocated(label)) &
+    label = ''
+end function find_unlimited_dimension_name
+
 end module MOM_io_infra