langgraph: fix graph drawing for self-loops (#4688)

Fixes #4685

libs/langgraph/langgraph/pregel/draw.py

@@ -229,9 +229,10 @@ def draw_graph(
                 first, last = graph.extend(subgraph, prefix=name)
                 for idx, edge in enumerate(graph.edges):
                     if edge.source == name:
-                        graph.edges[idx] = edge.copy(source=cast(Node, last).id)
-                    elif edge.target == name:
-                        graph.edges[idx] = edge.copy(target=cast(Node, first).id)
+                        edge = edge.copy(source=cast(Node, last).id)
+                    if edge.target == name:
+                        edge = edge.copy(target=cast(Node, first).id)
+                    graph.edges[idx] = edge
 
         return graph
 

libs/langgraph/tests/__snapshots__/test_pregel.ambr

@@ -396,6 +396,68 @@
   
   '''
 # ---
+# name: test_get_graph_self_loop
+  '''
+  {
+    "nodes": [
+      {
+        "id": "__start__",
+        "type": "runnable",
+        "data": {
+          "id": [
+            "langchain",
+            "schema",
+            "runnable",
+            "RunnablePassthrough"
+          ],
+          "name": "__start__"
+        }
+      },
+      {
+        "id": "worker_node",
+        "type": "runnable",
+        "data": {
+          "id": [
+            "langgraph",
+            "utils",
+            "runnable",
+            "RunnableCallable"
+          ],
+          "name": "worker_node"
+        }
+      },
+      {
+        "id": "__end__"
+      }
+    ],
+    "edges": [
+      {
+        "source": "__start__",
+        "target": "worker_node"
+      },
+      {
+        "source": "worker_node",
+        "target": "__end__",
+        "conditional": true
+      },
+      {
+        "source": "worker_node",
+        "target": "worker_node",
+        "conditional": true
+      }
+    ]
+  }
+  '''
+# ---
+# name: test_get_graph_self_loop.1
+  '''
+  graph TD;
+  	__start__ --> worker_node;
+  	worker_node -.-> __end__;
+  	worker_node -.-> worker_node;
+  
+  '''
+# ---
 # name: test_in_one_fan_out_state_graph_defer_node[memory-False]
   '''
   graph TD;

libs/langgraph/tests/test_pregel.py

@@ -8727,3 +8727,30 @@ def test_get_graph_loop(snapshot: SnapshotAssertion) -> None:
     app = workflow.compile()
     assert json.dumps(app.get_graph().to_json(), indent=2) == snapshot
     assert app.get_graph().draw_mermaid(with_styles=False) == snapshot
+
+
+def test_get_graph_self_loop(snapshot: SnapshotAssertion) -> None:
+    import random
+
+    subgraph_builder = StateGraph(MessagesState)
+    subgraph_builder.add_node("agent", lambda x: x)
+    subgraph_builder.add_edge(START, "agent")
+    subgraph = subgraph_builder.compile()
+
+    def worker_node(state: MessagesState) -> Command[Literal["worker_node", "__end__"]]:
+        subgraph_result = subgraph.invoke(state)
+
+        if random.choice([True, False]):
+            next_node_name = "worker_node"
+        else:
+            next_node_name = END
+
+        return Command(update=subgraph_result, goto=next_node_name)
+
+    self_loop_builder = StateGraph(MessagesState)
+    self_loop_builder.add_node("worker_node", worker_node)
+    self_loop_builder.add_edge(START, "worker_node")
+    self_loop_graph = self_loop_builder.compile()
+
+    assert json.dumps(self_loop_graph.get_graph().to_json(), indent=2) == snapshot
+    assert self_loop_graph.get_graph().draw_mermaid(with_styles=False) == snapshot