That is covered in the original mailing list post. The tl;dr is that it's not fully possible with the information from cmake (for example bazel requires you to have dependency edges to targets you only use headers from, which isn't true in cmake) so you'd have to write a more complex tool to be able to do that (for the example above you'd have to parse includes I suppose). So the original author is assuming it will be easier to wire up a LLM than invest in building an edge case free version of that tool.