feat: allow passing kernel manager to parser

[flying-sheep]

Hi, I built sphinx-exec-jupyter to leverage myst-nb’s machinery for running code blocks in isolation.

In it, I’m using a custom KernelClient for efficiency.

This client needs to be passed down all the way to executenb, and it would be great if that was possible without monkeypatching myst-nb.

Usage

It can be used directly when using a Parser programmaticly:

from myst_nb.sphinx_ import Parser

parser = Parser(km=MyKernelManager())
parser.parse(...)

… or by overriding the registered parser in a Sphinx extension like this:

from docutils import nodes
from myst_nb.sphinx_ import Parser

class SomeKernelManager(...): ...

class MyParser(Parser):
    # could override in `__init__` or here
    def parse(self, inputstring: str, document: nodes.document) -> None:
        self.km = MyKernelManager(document.settings.env)
        return super().parse(inputstring, document)

def setup(app):
    app.setup_extension("myst_nb")
    app.add_source_parser(MyParser, override=True)

Possible alternatives

• Instead of adding the km property to the parser and passing them to create_client, we could wrap create_client into a method on Parser, then I could override it. The other changes would still be necessary.

• In addition to the above method, I could break up parse into more granular steps in general for easier extensibility.