Support using beartype and MyST-Parser for creating a custom role which requires an Inliner

[adamtheturtle]

Describe the feature you'd like to request

Goals

• Create a custom role which extends docutils.parsers.rst.roles.code_role.
• Pass static type checking (mypy)
• Pass runtime type checking (beartype)

Below is a minimized example of my work towards supporting MyST for substitution-code within https://github.com/adamtheturtle/sphinx-substitution-extensions.

Requirements

• beartype==0.19.0
• myst-parser==4.0.0
• types-docutils==0.21.0.20241128

Files

Layout as described in
https://www.sphinx-doc.org/en/master/usage/configuration.html#confval-extensions.

<project directory>/
├── conf.py
└── sphinxext/
    └── extname.py

# conf.py

import sys
from pathlib import Path

# Path configured as per
# https://www.sphinx-doc.org/en/master/usage/configuration.html#confval-extensions
sys.path.append(str(Path('sphinxext').resolve()))

extensions = [
    "myst_parser",
    "extname",
]

# sphinxext/extname.py

from typing import Any

from beartype import beartype
from docutils.nodes import Node, system_message
from docutils.parsers.rst.roles import code_role
from docutils.parsers.rst.states import Inliner


# Typed version of the example from https://docutils.sourceforge.io/docs/howto/rst-roles.html#define-the-role-function
@beartype
def role_fn(
    name: str,
    rawtext: str,
    text: str,
    lineno: int,
    # This is an `Inliner`, so it can be passed through directly to `code_role`.
    inliner: Inliner,
    options: dict[Any, Any] = {},
    content: list[str] = [],
) -> tuple[list[Node], list[system_message]]:
    print("Custom logic")
    # Type stubs for `code_role` are at
    # https://github.com/python/typeshed/blob/57d7c4334b64856fda6f6e8f992b101ddafe2f57/stubs/docutils/docutils/parsers/rst/roles.pyi#L103
    #
    # Importantly, they require that `inliner` is an `Inliner`.
    return code_role(   
        role=name,
        rawtext=rawtext,
        text=text,
        lineno=lineno,
        inliner=inliner,
        options=options,
        content=content,
    )

@beartype
def setup(app):
    app.add_role(name="my-role", role=role_fn)

Command

sphinx-build -M html . build/

Error

beartype.roar.BeartypeCallHintParamViolation: Function extname.role_fn() parameter inliner=<myst_parser.mocking.MockInliner object at 0x10826e120> violates type hint <class 'docutils.parsers.rst.states.Inliner'>, as <class "myst_parser.mocking.MockInliner"> <myst_parser.mocking.MockInliner object at 0x10826e120> not instance of <class "docutils.parsers.rst.states.Inliner">.

Describe the solution you'd like

Modify MockInliner as per https://beartype.readthedocs.io/en/latest/faq/#mock-types to define a new __class__ property which returns Inliner.

Describe alternatives you've considered

My workaround is to have role_fn hint inliner as inliner: Inliner | MockInliner, and then to create a new Inliner object as needed for code_role:

if isinstance(inliner, MockInliner):
    new_inliner = Inliner()
    new_inliner.document = inliner_document
    inliner = new_inliner

Another alternative is to contribute to types-docutils to have code_role take a Protocol of just what is needed from Inliner, so it supports MockInliner, too.