fix(core): fix PydanticOutputParser's get_format_instructions for v1 models (#32479)

Author: cbornet

libs/core/langchain_core/output_parsers/pydantic.py

@@ -86,7 +86,7 @@ def get_format_instructions(self) -> str:
             The format instructions for the JSON output.
         """
         # Copy schema to avoid altering original Pydantic schema.
-        schema = dict(self.pydantic_object.model_json_schema().items())
+        schema = dict(self._get_schema(self.pydantic_object).items())
 
         # Remove extraneous fields.
         reduced_schema = schema

libs/core/tests/unit_tests/output_parsers/test_pydantic_parser.py

@@ -14,7 +14,7 @@
 from langchain_core.output_parsers import PydanticOutputParser
 from langchain_core.output_parsers.json import JsonOutputParser
 from langchain_core.prompts.prompt import PromptTemplate
-from langchain_core.utils.pydantic import PydanticBaseModel, TBaseModel
+from langchain_core.utils.pydantic import PydanticBaseModel, TypeBaseModel
 
 
 class ForecastV2(pydantic.BaseModel):
@@ -63,7 +63,7 @@ def test_pydantic_parser_chaining(
 
 
 @pytest.mark.parametrize("pydantic_object", _FORECAST_MODELS)
-def test_pydantic_parser_validation(pydantic_object: TBaseModel) -> None:
+def test_pydantic_parser_validation(pydantic_object: TypeBaseModel) -> None:
     bad_prompt = PromptTemplate(
         template="""{{
         "temperature": "oof",
@@ -75,9 +75,7 @@ def test_pydantic_parser_validation(pydantic_object: TBaseModel) -> None:
 
     model = ParrotFakeChatModel()
 
-    parser: PydanticOutputParser[PydanticBaseModel] = PydanticOutputParser(
-        pydantic_object=pydantic_object
-    )
+    parser = PydanticOutputParser[PydanticBaseModel](pydantic_object=pydantic_object)
     chain = bad_prompt | model | parser
     with pytest.raises(OutputParserException):
         chain.invoke({})
@@ -86,7 +84,7 @@ def test_pydantic_parser_validation(pydantic_object: TBaseModel) -> None:
 # JSON output parser tests
 @pytest.mark.parametrize("pydantic_object", _FORECAST_MODELS)
 def test_json_parser_chaining(
-    pydantic_object: TBaseModel,
+    pydantic_object: TypeBaseModel,
 ) -> None:
     prompt = PromptTemplate(
         template="""{{
@@ -194,6 +192,14 @@ class SampleModel(BaseModel):
     }
 
 
+@pytest.mark.parametrize("pydantic_object", _FORECAST_MODELS)
+def test_format_instructions(pydantic_object: TypeBaseModel) -> None:
+    """Test format instructions."""
+    parser = PydanticOutputParser[PydanticBaseModel](pydantic_object=pydantic_object)
+    instructions = parser.get_format_instructions()
+    assert "temperature" in instructions
+
+
 def test_format_instructions_preserves_language() -> None:
     """Test format instructions does not attempt to encode into ascii."""
     description = (