/// Flattens all file imports into a single string
    pub fn flatten(&self, target: &Path) -> Result<String> {
        tracing::trace!("flattening file");
        let mut input_files = self.input_files();

        // we need to ensure that the target is part of the input set, otherwise it's not
        // part of the graph if it's not imported by any input file
        let flatten_target = target.to_path_buf();
        if !input_files.contains(&flatten_target) {
            input_files.push(flatten_target);
        }

        let sources = Source::read_all_files(input_files)?;
        let graph = Graph::resolve_sources(self, sources)?;
        self.flatten_node(target, &graph, &mut Default::default(), false, false, false).map(|x| {
            format!("{}\n", utils::RE_THREE_OR_MORE_NEWLINES.replace_all(&x, "\n\n").trim())
        })
    }