Throw on preset w/ neither `settings` nor `plugins`

[wooorm]

Initial checklist

• [X] I read the support docs
• [X] I read the contributing guide
• [X] I agree to follow the code of conduct
• [X] I searched issues and couldn’t find anything (or linked relevant results below)

Problem

https://github.com/mdx-js/mdx/issues/2136

Solution

Throw here when neither plugins nor settings is defined.

Alternatives

Keep as is.

I don’t imagine most folks want empty presets being silently ignored.

For unified-engine, we treat config files as presets as well (though importing plugins-as-string). There might be a tiny use case there for empty config files, as they could “restore-to-defaults” a folder, if a higher folder has a config file that prescribes complex things. This would break that use case. But I dunno, I don’t think people actually do this?

[github-actions[bot]]

Hi! This was marked as ready to be worked on! Note that while this is ready to be worked on, nothing is said about priority: it may take a while for this to be solved.

Is this something you can and want to work on?

Team: please use the area/* (to describe the scope of the change), platform/* (if this is related to a specific one), and semver/* and type/* labels to annotate this. If this is first-timers friendly, add good first issue and if this could use help, add help wanted.