build TOC files next to sphinx xml

tocxml.py

import docutils
from docutils.io import StringOutput
import sphinx.builders.xml


class TOCXMLBuilder(sphinx.builders.xml.XMLBuilder):
    name = "tocxml"

    def write_doc(self, docname: str, doctree: docutils.nodes.document):
        print(f"write_doc {docname=} {doctree=}")
        from sphinx.environment.adapters.toctree import global_toctree_for_doc
        toctree = global_toctree_for_doc(self.env, docname, self)
        print(f"{toctree=}")
        print(toctree.pformat())

        super().write_doc(docname, doctree)

        for node in toctree.findall(docutils.nodes.Element):
            print(f"{node=}")
            node.reporter = None
        toctree.settings = doctree.settings
        toctree.reporter = doctree.reporter

        # This writer produces the wrong doctype, and we haven't dealt with any
        # namespacing.
        destination = StringOutput(encoding='utf-8')
        self.writer.write(toctree, destination)
        out_file_name = self.outdir / (docname + ".toc")
        out_file_name.parent.mkdir(parents=True, exist_ok=True)
        try:
            with open(out_file_name, 'w', encoding='utf-8') as f:
                f.write(self.writer.output)
        except OSError as err:
            logger.warning(__('error writing file %s: %s'), out_file_name, err)

def setup(app):
    app.add_builder(TOCXMLBuilder)