feat(remix-dev): add support for handle, links & loader to mdx

[TAGraves]

This adds a handle export, links export, and loader export to MDX routes, much like the existing meta and headers exports.

Closes: #2592, #2858

• Docs
• Tests

Testing Strategy:
I added a new integration test for mdx routes which covers the existing functionality (I believe this was uncovered before) as well as the newly added functionality.

I can see a couple different approaches for doing this. One option would be to just make the handle the frontmatter and omit the loader altogether. We could also structure the loader as:

{
  frontmatter: {/* ... */}
}

[changeset-bot]

🦋 Changeset detected

Latest commit: cea4a3e

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 16 packages

Name	Type
remix	Patch
@remix-run/dev	Patch
create-remix	Patch
@remix-run/eslint-config	Patch
@remix-run/react	Patch
@remix-run/serve	Patch
@remix-run/server-runtime	Patch
@remix-run/cloudflare	Patch
@remix-run/node	Patch
@remix-run/deno	Patch
@remix-run/cloudflare-pages	Patch
@remix-run/cloudflare-workers	Patch
@remix-run/express	Patch
@remix-run/netlify	Patch
@remix-run/vercel	Patch
@remix-run/architect	Patch

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[remix-cla-bot]

Thank you for signing the Contributor License Agreement. Let's get this merged! 🥳

[kentcdodds]

Thanks!

[github-actions]

🤖 Hello there,

We just published version v0.0.0-nightly-b2ef490-20220717 which includes this pull request. If you'd like to take it for a test run please try it out and let us know what you think!

Thanks!

[andreiduca]

I wonder why is the entire attributes object exported as the loader?

export const loader = typeof attributes === "undefined" ? undefined : () => attributes;

As I understand it, in Remix the loader is a server-side function that can retrieve data, interact with the request, and even read files from the disk. This PR makes it impossible to write such loader functions inside MDX files by setting the loader to whatever static data is defined in the frontmatter attributes.

👇🏻 This is currently possible in Remix, but won't be after this PR:

---
meta:
  title: Page with dynamic content
---

import { useLoaderData } from 'remix';
import { fetchSomeData } from ...

export const loader = async () => {
  const data = await fetchSomeData();
  return { data };
};

export function ComponentUsingData() {
  const { data } = useLoaderData();

  return <div>{data.whatever}</div>;
}

# This page has dynamic content

<ComponentUsingData />

[kentcdodds]

For some reason I didn't realize that would actually work. We haven't pushed this out yet as a release so I'll fix this before that happens.

[kentcdodds]

Here's the fix: #3800

[kentcdodds]

Actually. Thinking about it more... We already support links and handle. I'm going to revert this PR and I'll add docs for how you can do links and handle without any changes.

[kentcdodds]

Ok, so links won't work yet. But loader and handle do and I just pushed a docs update. We had some issues with our website recently (also, I just realized I pushed that to dev instead of main 😅) so those will take a little while to get up, but you can find it here: https://github.com/remix-run/remix/blob/dev/docs/guides/mdx.md#advanced-example

[TAGraves]

@kentcdodds Those approaches won't work for plain markdown files since they require the x in mdx 😄.

Here's a fairly simple thing we wanted to do in a layout route: take the meta.title field from our blogposts and put it in an H1 at the top of the page. Even using mdx I now need every blog post to know that the parent wants to do that and I have to include a handle or loader in every blog post to facilitate having the layout route inspect that data.

It'd be cool if we could detect if the markdown defines its own handle or loader and avoid overriding them if so. I'd be happy to take a stab at that.

[kentcdodds]

@TAGraves, thanks for the offer. We're not planning on investing any further in our markdown/mdx support. Build-time compilation of content is not the best UX/DX and we have other priorities as well (even reviewing PRs takes time). That said I did just make a PR (#3801) to support the links export capability for mdx files (though I believe that should work for plain markdown files as well because I think we treat them the same in Remix).

Here's what I suggest. Either:

1. Switch to using runtime compilation (with caching) via mdx-bundler. This allows you to update your content without rebuilding your whole site.
2. Do what's being done in https://github.com/kentcdodds/remix-mdx to completely customize how your mdx gets built

We do have ideas of things we can do to more fully customize the build-time markdown/mdx experience, but that's further down the pipeline.

[kentcdodds]

Oh, also I want to say thank you for your contribution here @TAGraves. I just realized that I reverted your addition to the contributors.yml file but then used the test you wrote. I'm going to add you to the other PR if that's ok with you. Normally this isn't the way we like doing open source (we really prefer giving git-credit to the people who wrote the code), I just wasn't thinking when I copy/pasted your test in my other commit. Sorry about that. And thank you for the contribution!