Fix issue 3152 - convert nbdev directives to YAML

[sswam]

Description

(This likely needs more work and testing.)

Quarto assumes that #| directive lines are valid YAML, but nbdev directives aren't.

I've come up with a somewhat hacky workaround, which converts any nbdev directive foo to foo: null before attempting to parse it as YAML, e.g.:

#| default_exp foo
#| export

is changed to:

#| default_exp foo: null
#| export: null

When writing a code cell, it strips off the null value and just shows the plain nbdev directive again. I'm assuming that Quarto directives don't ever use a value of "null".

With these changes, it seems to be stripping the nbdev directives out of my blog posts when rendering from ipynb, and that's okay with me.

It can't currently render from qmd format if these nbdev directives are used. We would need to adjust something in how it's reading the YAML there too.

Checklist

I have (if applicable):

• filed a contributor agreement.
• referenced the GitHub issue this PR closes
• updated the appropriate changelog

It's not much code, please let me know if you do want to use it and you require me to file a contributor agreement.

[cscheid]

Thanks for the PR, we appreciate it!. We're only going to be able to look at it carefully enough in a few weeks when our 1.3 release is finalized. I just wanted to make sure you know we're not ignoring this.

[ghost]

Thanks for contributing @sswam.

[seeM]

@cscheid, I believe this has been addressed by #3152, and you may close this PR.

Nbdev users can end directives with a trailing : (e.g. #| hide becomes #| hide:) which should work well with Quarto in both the ipynb to qmd case and vice versa.

[cscheid]

@seeM That's what I had thought as well. Thanks for confirming it!

@sswam I think you might be running an old version of quarto, since we merged a fix for #3152 in March. I'm going to go ahead and close this; feel free to follow up if you have a case that doesn't work for you.