Function process_doc 

pub fn process_doc(
    env: &mut BuildEnvironment,
    doc: &DocumentSource<'_>,
    doc2path: &dyn Fn(&str) -> PathBuf,
    warnings: &mut Vec<BuildWarning>,
)

StandardDomain.process_doc (domains/std/__init__.py:937-993) plus the registrations Sphinx performs from directives at parse time, which our parse layer has no domain callbacks to run: glossary terms (make_glossary_term) are replayed from the finished doctree, and the option/envvar/confval registrations (ObjectDescription.add_target_and_index) from the records the parse layer kept — see RegistryExport::program_options for why the doctree cannot carry those. The py domain’s registrations ([crate::env::py_domain::collect_registrations]) replay in the same parse-time pass, because that is where they fire in Sphinx — their duplicate warnings interleave with std’s in document order.

doc2path renders another document’s source path for the duplicate-label warning [ENV §8 #1], which names the path, not the docname.