Field copy - return if both fields point to the same data (#4713)

* MAPL_GridCompAddSpec: rename default_value -> fill_value

Also propagate the name change downstream to VariableSpec and state item specs (Field, Bracket, Vector) and affected routines

* FieldCopy: return early if both fields point to the same data

* Make FieldBundleCopy available to users

* Fixed tests

* Fixed tests

---------

Co-authored-by: Tom Clune <thomas.l.clune@nasa.gov>

Author: pchakraborty

field/FieldPointerUtilities.F90

@@ -3,7 +3,7 @@
 module MAPL_FieldPointerUtilities
    use ESMF
    use MAPL_ExceptionHandling
-   use, intrinsic :: iso_c_binding, only: c_ptr, c_f_pointer, c_loc
+   use, intrinsic :: iso_c_binding, only: c_ptr, c_f_pointer, c_loc, c_associated
    implicit none
    private
 
@@ -788,20 +788,21 @@ subroutine copy(x, y, rc)
       logical :: conformable
       logical :: x_is_double
       logical :: y_is_double
-      character(len=*), parameter :: UNSUPPORTED_TK = &
-         'Unsupported typekind in FieldCOPY() for '
+      character(len=*), parameter :: UNSUPPORTED_TK = 'Unsupported typekind in FieldCOPY() for '
 
       conformable = FieldsAreConformable(x, y)
       !wdb fixme need to pass RC
       _ASSERT(conformable, 'FieldCopy() - fields not conformable.')
+
       call FieldGetCptr(x, cptr_x, _RC)
+      call FieldGetCptr(y, cptr_y, _RC)
+      _RETURN_IF(c_associated(cptr_x, cptr_y)) ! nothing to copy if both point to the same data
+
       call ESMF_FieldGet(x, typekind = tk_x, _RC)
+      call ESMF_FieldGet(y, typekind = tk_y, _RC)
 
       n  = FieldGetLocalSize(x, _RC)
 
-      call FieldGetCptr(y, cptr_y, _RC)
-      call ESMF_FieldGet(y, typekind = tk_y, _RC)
-
       !wdb  fixme convert between precisions ? get rid of extra cases
       y_is_double = (tk_y == ESMF_TYPEKIND_R8)
       _ASSERT(y_is_double .or. (tk_y == ESMF_TYPEKIND_R4), UNSUPPORTED_TK//'y.')
@@ -919,7 +920,7 @@ subroutine MAPL_FieldGetLocalElementCount(field,local_count,rc)
          end select
          _RETURN(_SUCCESS)
       end if
-      
+
       if (tk == ESMF_TypeKind_R8) then
          select case(rank)
          case(1)

field_bundle/API.F90

@@ -10,6 +10,7 @@ module mapl3g_FieldBundle_API
    use mapl3g_FieldBundleInfo, only: MAPL_FieldBundleInfoGetInternal => FieldBundleInfoGetInternal
    use mapl3g_FieldBundleInfo, only: MAPL_FieldBundleInfoSetInternal => FieldBundleInfoSetInternal
    use mapl3g_FieldBundleGetPointer, only: MAPL_FieldBundleGetPointer => FieldBundleGetPointerToData
+   use mapl3g_FieldBundleCopy, only: MAPL_FieldBundleCopy => FieldBundleCopy
 
    implicit none
 
@@ -22,6 +23,7 @@ module mapl3g_FieldBundle_API
    public :: MAPL_FieldBundleSet
    public :: MAPL_FieldBundleAdd
    public :: MAPL_FieldBundleGetPointer
+   public :: MAPL_FieldBundleCopy
    ! Maybe these should be private?
    public :: MAPL_FieldBundleInfoGetInternal
    public :: MAPL_FieldBundleInfoSetInternal