Make abstract types abstract

Author: GlassOfWhiskey

schema_salad/metaschema.py

@@ -1187,7 +1187,7 @@ def parser_info() -> str:
 
 
 @trait
-class Documented(Saveable):
+class Documented(Saveable, metaclass=ABCMeta):
     pass
 
 
@@ -3480,17 +3480,17 @@ def __init__(
 
 
 @trait
-class NamedType(Saveable):
+class NamedType(Saveable, metaclass=ABCMeta):
     pass
 
 
 @trait
-class DocType(Documented):
+class DocType(Documented, metaclass=ABCMeta):
     pass
 
 
 @trait
-class SchemaDefinedType(DocType):
+class SchemaDefinedType(DocType, metaclass=ABCMeta):
     """
     Abstract base for schema-defined types.
 

schema_salad/python_codegen.py

@@ -162,6 +162,7 @@ def begin_class(
             ext = "Saveable"
 
         if self.current_class_is_abstract:
+            ext += ", metaclass=ABCMeta"
             decorator = "@trait\n"
         else:
             decorator = ""