core[patch]: Update remaining root_validators (#22829)

This PR updates the remaining root_validators in core to either be explicit pre-init or post-init validators.

libs/core/langchain_core/language_models/chat_models.py

@@ -120,7 +120,7 @@ class BaseChatModel(BaseLanguageModel[BaseMessage], ABC):
     callback_manager: Optional[BaseCallbackManager] = Field(default=None, exclude=True)
     """[DEPRECATED] Callback manager to add to the run trace."""
 
-    @root_validator()
+    @root_validator(pre=True)
     def raise_deprecation(cls, values: Dict) -> Dict:
         """Raise deprecation warning if callback_manager is used."""
         if values.get("callback_manager") is not None:

libs/core/langchain_core/language_models/llms.py

@@ -232,7 +232,7 @@ class BaseLLM(BaseLanguageModel[str], ABC):
 
         arbitrary_types_allowed = True
 
-    @root_validator()
+    @root_validator(pre=True)
     def raise_deprecation(cls, values: Dict) -> Dict:
         """Raise deprecation warning if callback_manager is used."""
         if values.get("callback_manager") is not None:

libs/core/langchain_core/messages/ai.py

@@ -149,7 +149,7 @@ class AIMessageChunk(AIMessage, BaseMessageChunk):
             "invalid_tool_calls": self.invalid_tool_calls,
         }
 
-    @root_validator()
+    @root_validator(pre=False, skip_on_failure=True)
     def init_tool_calls(cls, values: dict) -> dict:
         if not values["tool_call_chunks"]:
             values["tool_calls"] = []

libs/core/langchain_core/prompts/few_shot.py

@@ -121,7 +121,7 @@ class FewShotPromptTemplate(_FewShotPromptTemplateMixin, StringPromptTemplate):
     template_format: Literal["f-string", "jinja2"] = "f-string"
     """The format of the prompt template. Options are: 'f-string', 'jinja2'."""
 
-    @root_validator()
+    @root_validator(pre=False, skip_on_failure=True)
     def template_is_valid(cls, values: Dict) -> Dict:
         """Check that prefix, suffix, and input variables are consistent."""
         if values["validate_template"]:

libs/core/langchain_core/prompts/few_shot_with_templates.py

@@ -64,7 +64,7 @@ class FewShotPromptWithTemplates(StringPromptTemplate):
 
         return values
 
-    @root_validator()
+    @root_validator(pre=False, skip_on_failure=True)
     def template_is_valid(cls, values: Dict) -> Dict:
         """Check that prefix, suffix, and input variables are consistent."""
         if values["validate_template"]:

libs/core/langchain_core/prompts/prompt.py

@@ -47,7 +47,7 @@ class PromptTemplate(StringPromptTemplate):
             prompt.format(foo="bar")
 
             # Instantiation using initializer
-            prompt = PromptTemplate(input_variables=["foo"], template="Say {foo}")
+            prompt = PromptTemplate(template="Say {foo}")
     """
 
     @property
@@ -74,6 +74,43 @@ class PromptTemplate(StringPromptTemplate):
     validate_template: bool = False
     """Whether or not to try validating the template."""
 
+    @root_validator(pre=True)
+    def pre_init_validation(cls, values: Dict) -> Dict:
+        """Check that template and input variables are consistent."""
+        if values.get("template") is None:
+            # Will let pydantic fail with a ValidationError if template
+            # is not provided.
+            return values
+
+        # Set some default values based on the field defaults
+        values.setdefault("template_format", "f-string")
+        values.setdefault("partial_variables", {})
+
+        if values.get("validate_template"):
+            if values["template_format"] == "mustache":
+                raise ValueError("Mustache templates cannot be validated.")
+
+            if "input_variables" not in values:
+                raise ValueError(
+                    "Input variables must be provided to validate the template."
+                )
+
+            all_inputs = values["input_variables"] + list(values["partial_variables"])
+            check_valid_template(
+                values["template"], values["template_format"], all_inputs
+            )
+
+        if values["template_format"]:
+            values["input_variables"] = [
+                var
+                for var in get_template_variables(
+                    values["template"], values["template_format"]
+                )
+                if var not in values["partial_variables"]
+            ]
+
+        return values
+
     def get_input_schema(self, config: RunnableConfig | None = None) -> type[BaseModel]:
         if self.template_format != "mustache":
             return super().get_input_schema(config)
@@ -126,26 +163,6 @@ class PromptTemplate(StringPromptTemplate):
         kwargs = self._merge_partial_and_user_variables(**kwargs)
         return DEFAULT_FORMATTER_MAPPING[self.template_format](self.template, **kwargs)
 
-    @root_validator()
-    def template_is_valid(cls, values: Dict) -> Dict:
-        """Check that template and input variables are consistent."""
-        if values["validate_template"]:
-            if values["template_format"] == "mustache":
-                raise ValueError("Mustache templates cannot be validated.")
-            all_inputs = values["input_variables"] + list(values["partial_variables"])
-            check_valid_template(
-                values["template"], values["template_format"], all_inputs
-            )
-        elif values.get("template_format"):
-            values["input_variables"] = [
-                var
-                for var in get_template_variables(
-                    values["template"], values["template_format"]
-                )
-                if var not in values["partial_variables"]
-            ]
-        return values
-
     @classmethod
     def from_examples(
         cls,