Improve draw_mermaid Graph Readability for Multiple Nodes of the Same Type

[antwhite]

Checked

• I searched existing ideas and did not find a similar one
• I added a very descriptive title
• I've clearly described the feature request and motivation for it

Feature request

When a chain includes multiple nodes of the same type, node_id is used to distinguish them. This results in output from draw_mermaid that is often ineffective, especially in complex chains."

Example:

from langchain_core.runnables import RunnablePassthrough

def fake_llm(prompt: str) -> str: # Fake LLM for the example
    return "completion"

runnable = {
    'llm1':  fake_llm,
    'llm2':  fake_llm,
} | RunnablePassthrough.assign(
    total_chars=lambda inputs: len(inputs['llm1'] + inputs['llm2'])
)

print(runnable.get_graph().draw_mermaid(with_styles=False))

graph TD;
	Parallel_llm1_llm2_Input --> 0b01139db5ed4587ad37964e3a40c0ec;
	0b01139db5ed4587ad37964e3a40c0ec --> Parallel_llm1_llm2_Output;
	Parallel_llm1_llm2_Input --> a98d4b56bd294156a651230b9293347f;
	a98d4b56bd294156a651230b9293347f --> Parallel_llm1_llm2_Output;
	Parallel_total_chars_Input --> Lambda;
	Lambda --> Parallel_total_chars_Output;
	Parallel_total_chars_Input --> Passthrough;
	Passthrough --> Parallel_total_chars_Output;
	Parallel_llm1_llm2_Output --> Parallel_total_chars_Input;

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Motivation

I am documenting the chains used in our current application and many if not all have duplicate nodes.

Proposal (If applicable)

Alter

langchain/libs/core/langchain_core/runnables/graph.py

Lines 423 to 448 in 9ccd4a6

	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())
	def _get_node_id(node_id: str) -> str:
	label = node_labels[node_id]
	if is_uuid(node_id) and node_label_counts[label] == 1:
	return label
	else:
	return node_id
	return Graph(
	nodes={
	_get_node_id(id): node.copy(id=_get_node_id(id))
	for id, node in self.nodes.items()
	},
	edges=[
	edge.copy(
	source=_get_node_id(edge.source),
	target=_get_node_id(edge.target),
	)
	for edge in self.edges
	],
	)

so that node id is not returned but a more useful description. Perhaps disambiguate with a number ?

[antwhite]

I'm happy to contribute to a solution to this