fix mypy

Author: sycai

bigframes/operations/ai_ops.py

@@ -37,7 +37,7 @@ class AIGenerate(base_ops.NaryOp):
 
     def output_type(self, *input_types: dtypes.ExpressionType) -> dtypes.ExpressionType:
         if self.output_schema is None:
-            output_fields = [pa.field("result", pa.string())]
+            output_fields = (pa.field("result", pa.string()),)
         else:
             output_fields = output_schemas.parse_sql_fields(self.output_schema)
 

bigframes/operations/output_schemas.py

@@ -49,7 +49,8 @@ def parse_sql_type(sql: str) -> pa.DataType:
 
     if sql.startswith("STRUCT<") and sql.endswith(">"):
         inner_fields = parse_sql_fields(sql[len("STRUCT<") : -1])
-        return pa.struct(parse_sql_fields(inner_fields))
+
+        return pa.struct(sorted(inner_fields, key=lambda f:f.name))
 
     raise ValueError(f"Unsupported SQL type: {sql}")