Add validation of UDF parameters and return types (#83)

* Add validation of UDF parameters and return types

* Fix polars issues

Author: kesmit13

singlestoredb/functions/decorator.py

@@ -45,23 +45,20 @@ def is_valid_type(obj: Any) -> bool:
     return False
 
 
-def is_valid_callable(obj: Any) -> bool:
+def is_sqlstr_callable(obj: Any) -> bool:
     """Check if the object is a valid callable for a parameter type."""
     if not callable(obj):
         return False
 
     returns = utils.get_annotations(obj).get('return', None)
 
-    if inspect.isclass(returns) and issubclass(returns, str):
+    if inspect.isclass(returns) and issubclass(returns, SQLString):
         return True
 
-    raise TypeError(
-        f'callable {obj} must return a str, '
-        f'but got {returns}',
-    )
+    return False
 
 
-def expand_types(args: Any) -> Optional[Union[List[str], Type[Any]]]:
+def expand_types(args: Any) -> Optional[List[Any]]:
     """Expand the types for the function arguments / return values."""
     if args is None:
         return None
@@ -70,28 +67,32 @@ def expand_types(args: Any) -> Optional[Union[List[str], Type[Any]]]:
     if isinstance(args, str):
         return [args]
 
-    # General way of accepting pydantic.BaseModel, NamedTuple, TypedDict
-    elif is_valid_type(args):
-        return args
-
     # List of SQL strings or callables
     elif isinstance(args, list):
-        new_args = []
+        new_args: List[Any] = []
         for arg in args:
             if isinstance(arg, str):
                 new_args.append(arg)
-            elif callable(arg):
+            elif is_sqlstr_callable(arg):
                 new_args.append(arg())
+            elif type(arg) is type:
+                new_args.append(arg)
+            elif is_valid_type(arg):
+                new_args.append(arg)
             else:
                 raise TypeError(f'unrecognized type for parameter: {arg}')
         return new_args
 
     # Callable that returns a SQL string
-    elif is_valid_callable(args):
-        out = args()
-        if not isinstance(out, str):
-            raise TypeError(f'unrecognized type for parameter: {args}')
-        return [out]
+    elif is_sqlstr_callable(args):
+        return [args()]
+
+    # General way of accepting pydantic.BaseModel, NamedTuple, TypedDict
+    elif is_valid_type(args):
+        return [args]
+
+    elif type(args) is type:
+        return [args]
 
     raise TypeError(f'unrecognized type for parameter: {args}')