fix(python): handle non union self referencing schemas

generators/python/sdk/versions.yml

@@ -1,4 +1,13 @@
 # For unreleased changes, use unreleased.yml
+- version: 4.0.0-rc3
+  irVersion: 53
+  changelogEntry:
+    - type: fix
+      summary: | 
+        Pydantic models now call update forward refs on non-uion circular references. This 
+        prevents runtime errors in certain cases where types self reference itself through 
+        a union. 
+
 - version: 4.0.0-rc2
   irVersion: 53
   changelogEntry:

generators/python/src/fern_python/generators/context/pydantic_generator_context.py

@@ -68,6 +68,10 @@ def get_class_reference_for_type_id(
     def does_circularly_reference_itself(self, type_id: ir_types.TypeId) -> bool:
         ...
 
+    @abstractmethod
+    def get_non_union_circular_references(self) -> Set[ir_types.TypeId]:
+        ...
+
     @abstractmethod
     def do_types_reference_each_other(self, a: ir_types.TypeId, b: ir_types.TypeId) -> bool:
         ...

generators/python/src/fern_python/generators/context/pydantic_generator_context_impl.py

@@ -44,6 +44,15 @@ def __init__(
         self._allow_leveraging_defaults = allow_leveraging_defaults
         self._reserved_names: Set[str] = reserved_names or set()
 
+        self._non_union_self_referencing_type_ids = set()
+        for id, type in self.ir.types.items():
+            if (
+                id in type.referenced_types
+                and type.shape.get_as_union().type != "union"
+                and type.shape.get_as_union().type != "undiscriminatedUnion"
+            ):
+                self._non_union_self_referencing_type_ids.add(id)
+
     def get_module_path_in_project(self, module_path: AST.ModulePath) -> AST.ModulePath:
         return self._project_module_path + module_path
 
@@ -135,6 +144,9 @@ def get_class_reference_for_type_id(
     def does_circularly_reference_itself(self, type_id: ir_types.TypeId) -> bool:
         return self.does_type_reference_other_type(type_id, type_id)
 
+    def get_non_union_circular_references(self) -> Set[ir_types.TypeId]:
+        return self._non_union_self_referencing_type_ids
+
     def do_types_reference_each_other(self, a: ir_types.TypeId, b: ir_types.TypeId) -> bool:
         return self.does_type_reference_other_type(a, b) and self.does_type_reference_other_type(b, a)
 

generators/python/src/fern_python/generators/pydantic_model/fern_aware_pydantic_model.py

@@ -186,15 +186,20 @@ def _type_id_for_forward_ref(self) -> Optional[ir_types.TypeId]:
 
     def _must_import_after_current_declaration(self, type_name: ir_types.DeclaredTypeName) -> bool:
         type_id_to_reference = self._type_id_for_forward_ref()
-        is_circular_reference = False
+        should_import_after = False
         if type_id_to_reference is not None:
-            is_circular_reference = self._context.does_type_reference_other_type(
+            should_import_after = self._context.does_type_reference_other_type(
                 type_id=type_name.type_id, other_type_id=type_id_to_reference
             )
 
-        if is_circular_reference:
+        is_referencing_circular_reference = type_name.type_id in self._context.get_non_union_circular_references()
+        if is_referencing_circular_reference:
+            should_import_after = is_referencing_circular_reference
+
+        if should_import_after:
             self._model_contains_forward_refs = True
-        return is_circular_reference
+
+        return should_import_after
 
     def add_method(
         self,