[DRAFT] Merge metadata props when fusing

onnxscript/rewriter/_rewrite_rule.py

@@ -531,6 +531,23 @@
                     f = ir.Function(domain, name, overload, graph=graph, attributes=())
                     model.functions[f.identifier()] = f
 
+                # If we are fusing nodes, update the docstring of the new node(s)
+                attributes = ["namespace", "pkg.torch.onnx.class_hierarchy", "pkg.torch.onnx.fx_node", "pkg.torch.onnx.name_scopes", "pkg.torch.onnx.stack_trace"]
+                if delta.match.nodes and delta.new_nodes:
+                    # Concatenate docstrings from all original nodes
+                    for attribute in attributes:
+                        fused_attribute = "\n".join(
+                            n.metadata_props[attribute] for n in delta.match.nodes if getattr(n, "metadata_props", None) and attribute in n.metadata_props
+                        )
+                        if fused_attribute.strip():
+                            fused_attribute = "Fused from nodes with following attributes: " + fused_attribute
+                            for node in delta.new_nodes:
+                                # Assign to all new nodes
+                                if attribute in node.metadata_props:
+                                    node.metadata_props[attribute] += f"\n{fused_attribute}"
+                                else:
+                                    node.metadata_props[attribute] = fused_attribute
+
                 if verbose:
                     name = f"{rule.name}: " if rule.name else ""
                     print(f"----{name}Matched Nodes----")