[F2C transpilation] (driver level) convert interface to import

loki/transformations/transpile/fortran_c.py

@@ -182,6 +182,7 @@ def transform_subroutine(self, routine, **kwargs):
             depth = depths[item]
 
         if role == 'driver':
+            self.interface_to_import(routine, targets)
             return
 
         for arg in routine.arguments:
@@ -243,6 +244,30 @@ def convert_kwargs_to_args(self, routine, targets):
         if inline_call_map:
             routine.body = SubstituteExpressions(inline_call_map).visit(routine.body)
 
+    def interface_to_import(self, routine, targets):
+        """
+        Convert interface to import.
+        """
+        for call in FindNodes(CallStatement).visit(routine.body):
+            if str(call.name).lower() in as_tuple(targets):
+                call.convert_kwargs_to_args()
+        intfs = FindNodes(Interface).visit(routine.spec)
+        removal_map = {}
+        for i in intfs:
+            for b in i.body:
+                if isinstance(b, Subroutine):
+                    if targets and b.name.lower() in targets:
+                        # Create a new module import with explicitly qualified symbol
+                        modname = f'{b.name}_FC_MOD'
+                        new_symbol = Variable(name=f'{b.name}_FC', scope=routine)
+                        new_import = Import(module=modname, c_import=False, symbols=(new_symbol,))
+                        routine.spec.prepend(new_import)
+                        # Mark current import for removal
+                        removal_map[i] = None
+        # Apply any scheduled interface removals to spec
+        if removal_map:
+            routine.spec = Transformer(removal_map).visit(routine.spec)
+
     def c_struct_typedef(self, derived):
         """
         Create the :class:`TypeDef` for the C-wrapped struct definition.

loki/transformations/transpile/tests/test_transpile.py

@@ -1372,6 +1372,50 @@ def init_var(dtype, val=0):
         fc_function(in_var, out_var)
         assert int(out_var) == expected_results[i]
 
+@pytest.mark.parametrize('frontend', available_frontends())
+def test_transpile_interface_to_module(tmp_path, frontend):
+    driver_fcode = """
+SUBROUTINE driver_interface_to_module(a, b, c)
+  IMPLICIT NONE
+  INTERFACE
+    SUBROUTINE KERNEL(a, b, c)
+      INTEGER, INTENT(INOUT) :: a, b, c
+    END SUBROUTINE KERNEL
+  END INTERFACE
+  INTERFACE
+    SUBROUTINE KERNEL2(a, b)
+      INTEGER, INTENT(INOUT) :: a, b
+    END SUBROUTINE KERNEL2
+  END INTERFACE
+  INTERFACE
+    SUBROUTINE KERNEL3(a)
+      INTEGER, INTENT(INOUT) :: a
+    END SUBROUTINE KERNEL3
+  END INTERFACE
+
+  INTEGER, INTENT(INOUT) :: a, b, c
+
+  CALL kernel(a, b ,c)
+  CALL kernel2(a, b)
+END SUBROUTINE driver_interface_to_module
+    """.strip()
+
+    routine = Subroutine.from_source(driver_fcode, frontend=frontend)
+
+    interfaces = FindNodes(ir.Interface).visit(routine.spec)
+    imports = FindNodes(ir.Import).visit(routine.spec)
+    assert len(interfaces) == 3
+    assert not imports
+
+    f2c = FortranCTransformation()
+    f2c.apply(source=routine, path=tmp_path, targets=('kernel',), role='driver')
+
+    interfaces = FindNodes(ir.Interface).visit(routine.spec)
+    imports = FindNodes(ir.Import).visit(routine.spec)
+    assert len(interfaces) == 2
+    assert len(imports) == 1
+    assert imports[0].module.upper() == 'KERNEL_FC_MOD'
+
 
 @pytest.fixture(scope='module', name='horizontal')
 def fixture_horizontal():