From 61e47cb137ed8735e863a54d9ef13deabf30f633 Mon Sep 17 00:00:00 2001
From: vbarda <vadym@langchain.dev>
Date: Wed, 27 Nov 2024 09:37:22 -0500
Subject: [PATCH 1/2] langgraph: relax graph validation to handle nodes without
 return typehints

---
 libs/langgraph/langgraph/graph/graph.py | 10 +++++---
 libs/langgraph/tests/test_pregel.py     | 33 +++++++++++++++----------
 2 files changed, 26 insertions(+), 17 deletions(-)

diff --git a/libs/langgraph/langgraph/graph/graph.py b/libs/langgraph/langgraph/graph/graph.py
index e91ac4a47..37fe90ebe 100644
--- a/libs/langgraph/langgraph/graph/graph.py
+++ b/libs/langgraph/langgraph/graph/graph.py
@@ -374,6 +374,11 @@ class Graph:
             if source not in self.nodes and source != START:
                 raise ValueError(f"Found edge starting at unknown node '{source}'")
 
+        if START not in all_sources:
+            raise ValueError(
+                "Graph must have an entrypoint: add at least one edge from START to another node"
+            )
+
         # assemble targets
         all_targets = {end for _, end in self._all_edges}
         for start, branches in self.branches.items():
@@ -392,13 +397,10 @@ class Graph:
                     for node in self.nodes:
                         if node != start and node != branch.then:
                             all_targets.add(node)
+
         for name, spec in self.nodes.items():
             if spec.ends:
                 all_targets.update(spec.ends)
-        # validate targets
-        for node in self.nodes:
-            if node not in all_targets:
-                raise ValueError(f"Node `{node}` is not reachable")
         for target in all_targets:
             if target not in self.nodes and target != END:
                 raise ValueError(f"Found edge ending at unknown node `{target}`")
diff --git a/libs/langgraph/tests/test_pregel.py b/libs/langgraph/tests/test_pregel.py
index fda881b15..f5a5cd673 100644
--- a/libs/langgraph/tests/test_pregel.py
+++ b/libs/langgraph/tests/test_pregel.py
@@ -164,7 +164,7 @@ def test_graph_validation() -> None:
     workflow = Graph()
     workflow.add_node("agent", logic)
     workflow.set_finish_point("agent")
-    with pytest.raises(ValueError, match="not reachable"):
+    with pytest.raises(ValueError, match="must have an entrypoint"):
         workflow.compile()
 
     workflow = Graph()
@@ -211,18 +211,6 @@ def test_graph_validation() -> None:
     with pytest.raises(ValueError, match="unknown"):  # extra is not defined
         workflow.compile()
 
-    workflow = Graph()
-    workflow.add_node("agent", logic)
-    workflow.add_node("tools", logic)
-    workflow.add_node("extra", logic)
-    workflow.set_entry_point("agent")
-    workflow.add_conditional_edges("agent", logic, {"continue": "tools", "exit": END})
-    workflow.add_edge("tools", "agent")
-    with pytest.raises(
-        ValueError, match="Node `extra` is not reachable"
-    ):  # extra is not reachable
-        workflow.compile()
-
     workflow = Graph()
     workflow.add_node("agent", logic)
     workflow.add_node("tools", logic)
@@ -280,6 +268,25 @@ def test_graph_validation() -> None:
         graph.invoke({"hello": "there"})
 
 
+def test_graph_validation_with_command() -> None:
+    class State(TypedDict):
+        foo: str
+        bar: str
+
+    def node_a(state: State):
+        return GraphCommand(goto="b", update={"foo": "bar"})
+
+    def node_b(state: State):
+        return GraphCommand(goto=END, update={"bar": "baz"})
+
+    builder = StateGraph(State)
+    builder.add_node("a", node_a)
+    builder.add_node("b", node_b)
+    builder.add_edge(START, "a")
+    graph = builder.compile()
+    assert graph.invoke({"foo": ""}) == {"foo": "bar", "bar": "baz"}
+
+
 def test_checkpoint_errors() -> None:
     class FaultyGetCheckpointer(MemorySaver):
         def get_tuple(self, config: RunnableConfig) -> Optional[CheckpointTuple]:

From f416480e9d81eaf3018eda2e80facd87a3251252 Mon Sep 17 00:00:00 2001
From: vbarda <vadym@langchain.dev>
Date: Wed, 27 Nov 2024 10:01:24 -0500
Subject: [PATCH 2/2] nit

---
 libs/langgraph/langgraph/graph/graph.py | 1 -
 1 file changed, 1 deletion(-)

diff --git a/libs/langgraph/langgraph/graph/graph.py b/libs/langgraph/langgraph/graph/graph.py
index 37fe90ebe..50a4dadfb 100644
--- a/libs/langgraph/langgraph/graph/graph.py
+++ b/libs/langgraph/langgraph/graph/graph.py
@@ -397,7 +397,6 @@ class Graph:
                     for node in self.nodes:
                         if node != start and node != branch.then:
                             all_targets.add(node)
-
         for name, spec in self.nodes.items():
             if spec.ends:
                 all_targets.update(spec.ends)