jambo/parser/const_type_parser.py

@@ -3,7 +3,7 @@ from jambo.types.json_schema_type import JSONSchemaNativeTypes
 from jambo.types.type_parser_options import TypeParserOptions
 
 from pydantic import AfterValidator
-from typing_extensions import Annotated, Any, Unpack
+from typing_extensions import Annotated, Any, Literal, Unpack
 
 
 class ConstTypeParser(GenericTypeParser):
@@ -33,11 +33,19 @@ class ConstTypeParser(GenericTypeParser):
         return const_type, parsed_properties
 
     def _build_const_type(self, const_value):
-        def _validate_const_value(value: Any) -> Any:
-            if value != const_value:
-                raise ValueError(
-                    f"Value must be equal to the constant value: {const_value}"
-                )
-            return value
+        # Try to use Literal for hashable types (required for discriminated unions)
+        # Fall back to validator approach for non-hashable types
+        try:
+            # Test if the value is hashable (can be used in Literal)
+            hash(const_value)
+            return Literal[const_value]
+        except TypeError:
+            # Non-hashable type (like list, dict), use validator approach
+            def _validate_const_value(value: Any) -> Any:
+                if value != const_value:
+                    raise ValueError(
+                        f"Value must be equal to the constant value: {const_value}"
+                    )
+                return value
 
-        return Annotated[type(const_value), AfterValidator(_validate_const_value)]
+            return Annotated[type(const_value), AfterValidator(_validate_const_value)]

tests/parser/test_const_type_parser.py

@@ -1,12 +1,13 @@
 from jambo.parser import ConstTypeParser
 
-from typing_extensions import Annotated, get_args, get_origin
+from typing_extensions import Annotated, Literal, get_args, get_origin
 
 from unittest import TestCase
 
 
 class TestConstTypeParser(TestCase):
-    def test_const_type_parser(self):
+    def test_const_type_parser_hashable_value(self):
+        """Test const parser with hashable values (uses Literal)"""
         parser = ConstTypeParser()
 
         expected_const_value = "United States of America"
@@ -16,8 +17,60 @@ class TestConstTypeParser(TestCase):
             "country", properties
         )
 
+        # Check that we get a Literal type for hashable values
+        self.assertEqual(get_origin(parsed_type), Literal)
+        self.assertEqual(get_args(parsed_type), (expected_const_value,))
+
+        self.assertEqual(parsed_properties["default"], expected_const_value)
+
+    def test_const_type_parser_non_hashable_value(self):
+        """Test const parser with non-hashable values (uses Annotated with validator)"""
+        parser = ConstTypeParser()
+
+        expected_const_value = [1, 2, 3]  # Lists are not hashable
+        properties = {"const": expected_const_value}
+
+        parsed_type, parsed_properties = parser.from_properties_impl(
+            "list_const", properties
+        )
+
+        # Check that we get an Annotated type for non-hashable values
         self.assertEqual(get_origin(parsed_type), Annotated)
-        self.assertIn(str, get_args(parsed_type))
+        self.assertIn(list, get_args(parsed_type))
+
+        self.assertEqual(parsed_properties["default"], expected_const_value)
+
+    def test_const_type_parser_integer_value(self):
+        """Test const parser with integer values (uses Literal)"""
+        parser = ConstTypeParser()
+
+        expected_const_value = 42
+        properties = {"const": expected_const_value}
+
+        parsed_type, parsed_properties = parser.from_properties_impl(
+            "int_const", properties
+        )
+
+        # Check that we get a Literal type for hashable values
+        self.assertEqual(get_origin(parsed_type), Literal)
+        self.assertEqual(get_args(parsed_type), (expected_const_value,))
+
+        self.assertEqual(parsed_properties["default"], expected_const_value)
+
+    def test_const_type_parser_boolean_value(self):
+        """Test const parser with boolean values (uses Literal)"""
+        parser = ConstTypeParser()
+
+        expected_const_value = True
+        properties = {"const": expected_const_value}
+
+        parsed_type, parsed_properties = parser.from_properties_impl(
+            "bool_const", properties
+        )
+
+        # Check that we get a Literal type for hashable values
+        self.assertEqual(get_origin(parsed_type), Literal)
+        self.assertEqual(get_args(parsed_type), (expected_const_value,))
 
         self.assertEqual(parsed_properties["default"], expected_const_value)
 

tests/test_schema_converter.py

@@ -701,6 +701,29 @@ class TestSchemaConverter(TestCase):
         with self.assertRaises(ValueError):
             Model(name="Canada")
 
+    def test_const_type_parser_with_non_hashable_value(self):
+        schema = {
+            "title": "Country",
+            "type": "object",
+            "properties": {
+                "name": {
+                    "const": ["Brazil"],
+                }
+            },
+            "required": ["name"],
+        }
+
+        Model = SchemaConverter.build(schema)
+
+        obj = Model()
+        self.assertEqual(obj.name, ["Brazil"])
+
+        with self.assertRaises(ValueError):
+            obj.name = ["Argentina"]
+
+        with self.assertRaises(ValueError):
+            Model(name=["Argentina"])
+
     def test_null_type_parser(self):
         schema = {
             "title": "Test",