How Sphinx Default Role Works

What is "default role"?

The default role (`content`) has no special meaning by default. You are free to use it for anything you like, e.g. variable names; use the default_role config value to set it to a known role – the any role to find anything or the py:obj role to find Python objects are very useful for this.

—— https://www.sphinx-doc.org/en/master/usage/restructuredtext/roles.html#roles

小技巧

::`content` is equal to `content`, and both of them have same interpreted text "content" and rolename name "" (an empty string).

How it works? The principle is temporarily registering the default role with an empty string when parsing.

Setup "default role"

Default-role can be configured by directive default-role (doc-level) or confval default_role (project-level).

Default Role Registration

Current there are tow ways for registering default role, one for doc-level and one for project-level.

Project-level Registration

The sphinx.docutils.rst.default_role() is a contextlib.contextmanager. As context of with clause: when entering clause, function register the default role with empty string, when leaving, unregister it

@contextmanager
def default_role(docname: str, name: str) -> Iterator[None]:
    if name:
        dummy_reporter = Reporter('', 4, 4)
        role_fn, _ = roles.role(name, english, 0, dummy_reporter)
        if role_fn:
            docutils.register_role('', role_fn)  # type: ignore[arg-type]
        else:
            logger.warning(__('default role %s not found'), name, location=docname)

    yield

    docutils.unregister_role('')

提示

We can learn docutils.parsers.rst.roles.role() is a good way to lookup role funtion by name.

sphinx.builders.Builder use default_role context when parsing each document:

@final
def read_doc(self, docname: str, *, _cache: bool = True) -> None:
    """Parse a file and add/update inventory entries for the doctree."""

    # …
    with sphinx_domains(self.env), rst.default_role(docname, self.config.default_role):
        # set up error_handler for the target document
        codecs.register_error('sphinx',
                              UnicodeDecodeErrorHandler(docname))  # type: ignore[arg-type]

        publisher.set_source(source_path=filename)
        publisher.publish()
        doctree = publisher.document

    # …

Doc-level registration

Sphinx overrides docutils' default-role` implementation, use sphinx.directives.DefaultRole instead.

In the run method, directivees add default role name to sphinx.environment.BuildEnvironment.temp_data. temp_data is a document-independent storage.

备注

You may wonder why there is no logic for handling unregistering. In fact, the unregistering of the default role is always completed by the default_role context above.

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