MULTIPLE_SUBGRAPHS exception raised incorrectly

[eyurtsev]

Privileged issue

• I am a LangChain maintainer, or was asked directly by a LangChain maintainer to create an issue here.

Issue Content

This should probably be a different exception -- we're just returning the wrong thing (the subgraph instead of the return value from the subgraph)

import uuid
from typing import TypedDict, Optional

from langgraph.graph import StateGraph
from langgraph.constants import START 
from langgraph.checkpoint.memory import MemorySaver


class State(TypedDict):
    """The graph state."""
    state_counter: int

def child_node(state: State):
    return state


subgraph_builder = StateGraph(State)
subgraph_builder.add_node("child_node", child_node)
subgraph_builder.add_edge(START, "child_node")
subgraph = subgraph_builder.compile() 

def parent_node(state: State):
    """This parent node will invoke the subgraph."""
    subgraph_state = subgraph.invoke(state)
    return subgraph # <--- THIS IS THE BUG IN USER CODE (typo), exception claims multiple subgraph calls (based on ast parsing?)

checkpointer = MemorySaver()


builder = StateGraph(State)
builder.add_node("parent_node", parent_node)
builder.add_edge(START, "parent_node")

# A checkpointer must be enabled for interrupts to work!
checkpointer = MemorySaver()
graph = builder.compile(checkpointer=checkpointer)

config = {
    "configurable": {
        "thread_id": uuid.uuid4(),
    }
}

for chunk in graph.stream({"state_counter": 1}, config):
    print(chunk)

[isatyamks]

@eyurtsev Since the code now returns subgraph_state instead of state, it seems the issue is resolved. Let me know if I'm misunderstanding something