binding flow fix

Author: wpbonelli

flopy4/mf6/codec/reader/transformer.py

@@ -375,7 +375,8 @@ def __default__(self, data, children, meta):
                 return (data, child)
 
         # Handle keyword rules (no children) - return (name, True)
-        if not children:
+        # But not for _fields rules which may legitimately be empty
+        if not children and not data.endswith("_fields"):
             return (data, True)
 
         # Handle block rules (e.g., options_block, dimensions_block)
@@ -405,12 +406,16 @@ def __default__(self, data, children, meta):
                 elif isinstance(item, tuple):
                     field_tuples.append(item)
 
-            # For binding blocks (models, exchanges, solutiongroup), return just the
-            # records list. The _block handler will wrap it as {block_name: list},
-            # which is what the converter expects for binding resolution.
+            # For binding blocks (models, exchanges, solutiongroup), always return
+            # a list (possibly empty). The _block handler will wrap it as
+            # {block_name: list}, which is what the converter expects.
             # Note: solutiongroup has mxiter, but we ignore it here since the
             # Simulation class doesn't have a place for it yet.
-            if records and (not field_tuples or block_name == "solutiongroup"):
+            if block_name in ("models", "exchanges", "solutiongroup"):
+                return records
+
+            # For other blocks with only records (no scalar fields), return list
+            if records and not field_tuples:
                 return records
 
             # Build result dict from scalar fields

flopy4/mf6/converter/__init__.py

@@ -112,8 +112,9 @@ def _resolve_bindings_in_dict(data: dict, workspace: Path, target_type: type) ->
     """
     Resolve binding tuples in data dict to component instances.
 
-    Detects lists of binding tuples (e.g., [['gwf6', 'file.nam', 'name']])
-    and transforms them to component instances or dicts of instances.
+    Detects:
+    - Lists of binding tuples (e.g., [['gwf6', 'file.nam', 'name']])
+    - Scalar bindings (e.g., {'tdis6': 'simulation.tdis'})
 
     Parameters
     ----------
@@ -140,7 +141,18 @@ def _resolve_bindings_in_dict(data: dict, workspace: Path, target_type: type) ->
 
         value = resolved[field_name]
 
-        # Skip if not a list (no binding tuples to resolve)
+        # Handle scalar bindings: {'tdis6': 'filename.tdis'}
+        # These are dicts with a single key ending in '6'
+        if isinstance(value, dict) and len(value) == 1:
+            binding_key = next(iter(value.keys()))
+            if isinstance(binding_key, str) and binding_key.lower().endswith("6"):
+                binding_fname = value[binding_key]
+                binding_tuple = [binding_key, binding_fname]
+                component = Binding.to_component(binding_tuple, workspace)
+                resolved[field_name] = component
+                continue
+
+        # Handle list bindings
         if not isinstance(value, list):
             continue