core: use friendlier names for duplicated nodes in mermaid output

libs/core/langchain_core/runnables/graph.py

@@ -1,7 +1,7 @@
 from __future__ import annotations
 
 import inspect
-from collections import Counter
+from collections import defaultdict
 from collections.abc import Sequence
 from dataclasses import dataclass, field
 from enum import Enum
@@ -423,12 +423,19 @@ def prefixed(id: str) -> str:
     def reid(self) -> Graph:
         """Return a new graph with all nodes re-identified,
         using their unique, readable names where possible."""
-        node_labels = {node.id: node.name for node in self.nodes.values()}
-        node_label_counts = Counter(node_labels.values())
+        node_name_to_ids = defaultdict(list)
+        for node in self.nodes.values():
+            node_name_to_ids[node.name].append(node.id)
+
+        unique_labels = {
+            node_id: node_name if len(node_ids) == 1 else f"{node_name}_{i + 1}"
+            for node_name, node_ids in node_name_to_ids.items()
+            for i, node_id in enumerate(node_ids)
+        }
 
         def _get_node_id(node_id: str) -> str:
-            label = node_labels[node_id]
-            if is_uuid(node_id) and node_label_counts[label] == 1:
+            label = unique_labels[node_id]
+            if is_uuid(node_id):
                 return label
             else:
                 return node_id

libs/core/tests/unit_tests/runnables/__snapshots__/test_graph.ambr

@@ -26,6 +26,20 @@
 
   '''
 # ---
+# name: test_graph_mermaid_duplicate_nodes[mermaid]
+  '''
+  graph TD;
+  	PromptInput --> PromptTemplate_1;
+  	Parallel_llm1_llm2_Input --> FakeListLLM_1;
+  	FakeListLLM_1 --> Parallel_llm1_llm2_Output;
+  	Parallel_llm1_llm2_Input --> FakeListLLM_2;
+  	FakeListLLM_2 --> Parallel_llm1_llm2_Output;
+  	PromptTemplate_1 --> Parallel_llm1_llm2_Input;
+  	PromptTemplate_2 --> PromptTemplateOutput;
+  	Parallel_llm1_llm2_Output --> PromptTemplate_2;
+
+  '''
+# ---
 # name: test_graph_sequence[ascii]
   '''
               +-------------+              

libs/core/tests/unit_tests/runnables/test_graph.py

@@ -405,3 +405,17 @@ def test_graph_mermaid_escape_node_label() -> None:
     assert _escape_node_label("foo-bar") == "foo-bar"
     assert _escape_node_label("foo_1") == "foo_1"
     assert _escape_node_label("#foo*&!") == "_foo___"
+
+
+def test_graph_mermaid_duplicate_nodes(snapshot: SnapshotAssertion) -> None:
+    fake_llm = FakeListLLM(responses=["foo", "bar"])
+    sequence: Runnable = (
+        PromptTemplate.from_template("Hello, {input}")
+        | {
+            "llm1": fake_llm,
+            "llm2": fake_llm,
+        }
+        | PromptTemplate.from_template("{llm1} {llm2}")
+    )
+    graph = sequence.get_graph()
+    assert graph.draw_mermaid(with_styles=False) == snapshot(name="mermaid")