SingleColumn: Fix corner case of empty !$acc data clauses

Adds a small test and does not print data clauses if no arrays
are passed to the routine.

loki/transformations/single_column/annotate.py

@@ -135,9 +135,10 @@ def annotate_kernel_routine(self, routine):
         args += [a for a in routine.arguments if isinstance(a.type.dtype, DerivedType)]
         argnames = [str(a.name) for a in args]
 
-        routine.body.prepend(ir.Pragma(keyword='acc', content=f'data present({", ".join(argnames)})'))
-        # Add comment to prevent false-attachment in case it is preceded by an "END DO" statement
-        routine.body.append((ir.Comment(text=''), ir.Pragma(keyword='acc', content='end data')))
+        if argnames:
+            routine.body.prepend(ir.Pragma(keyword='acc', content=f'data present({", ".join(argnames)})'))
+            # Add comment to prevent false-attachment in case it is preceded by an "END DO" statement
+            routine.body.append((ir.Comment(text=''), ir.Pragma(keyword='acc', content='end data')))
 
     def transform_subroutine(self, routine, **kwargs):
         """

loki/transformations/single_column/tests/test_scc.py

@@ -789,6 +789,43 @@ def test_scc_annotate_routine_seq_pragma(frontend, horizontal, blocking):
     assert pragmas[0].content == 'routine seq'
 
 
+@pytest.mark.parametrize('frontend', available_frontends())
+def test_scc_annotate_empty_data_clause(frontend, horizontal, blocking):
+    """
+    Test that we do not generate empty `!$acc data` clauses.
+    """
+
+    fcode = """
+    subroutine some_kernel(n)
+       implicit none
+       ! Scalars should not show up in `!$acc data` clause
+       integer, intent(inout) :: n
+!$loki routine seq
+       integer :: k
+
+       k = n
+       do k=1, 3
+          n = k + 1.
+       enddo
+    end subroutine some_kernel
+    """
+    routine = Subroutine.from_source(fcode, frontend=frontend)
+
+    pragmas = FindNodes(Pragma).visit(routine.ir)
+    assert len(pragmas) == 1
+    assert pragmas[0].keyword == 'loki'
+    assert pragmas[0].content == 'routine seq'
+
+    transformation = SCCAnnotateTransformation(directive='openacc', block_dim=blocking)
+    transformation.transform_subroutine(routine, role='kernel', targets=['some_kernel',])
+
+    # Ensure the routine pragma is in the first pragma in the spec
+    pragmas = FindNodes(Pragma).visit(routine.ir)
+    assert len(pragmas) == 1
+    assert pragmas[0].keyword == 'acc'
+    assert pragmas[0].content == 'routine seq'
+
+
 @pytest.mark.parametrize('frontend', available_frontends())
 def test_scc_vector_reduction(frontend, horizontal, blocking):
     """