Add new markdown.frontmatterPlugins config option

[sylvinus]

Hello!

Currently, when importing Markdown files, one can modify their content via the markdown.remarkPlugins and markdown.rehypePlugins config options.

However there is currently no supported way to do the same with their frontmatter. This could open up interesting usecases:

• Auto-registering components in imported Markdown files (just append the imports to frontmatter.setup!)
• Provide a more generic solution to the frontmatterDefaults suggestion here: Simplify Markdown Layouts roadmap#172 (comment)
• Probably more that I'm missing!

This patch adds a prototype implementation of a new frontmatterPlugins config option.

Let me know what you think!

Thanks,

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[mattfelten]

Any progress on this @sylvinus? I'm really excited for this change

[sylvinus]

@mattfelten I'm excited for it as well! An official RFC has been created: withastro/roadmap#196 ; Not sure what/when the next steps are.

[delucis]

The RFC was accepted!

https://github.com/withastro/rfcs/blob/main/proposals/0022-frontmatter-plugins.md

Think the next step would be to get this PR polished and then it can be merged!

[sylvinus]

By the way in the meantime I've also been using a custom plugin to register all available components in Markdown files:

// src/plugins/inject-components.mjs
import glob from 'fast-glob';
import path from 'path';

export default (dir) => {
  let components = [];
  return {
    name: 'mdInjectComponentsPlugin',
    enforce: 'pre',
    options: async () => {
      components = await glob(dir.replace(/\/$/g, '') + '/**/*');
    },
    transform: (ctx, id) => {
      if (!id.match(/\.md$/)) {
        return false;
      }
      let prepend = "";
      for (const component of components) {
        let name = path.basename(component, path.extname(component));
        prepend += "import "+name+" from '"+component+"';\n";
      }
      ctx = prepend + "\n" + ctx;
      return ctx;
    },
  };
};

// astro.config.mjs
import { defineConfig } from 'astro/config';
import path from 'path';
import {fileURLToPath} from 'url';
import mdInjectComponentsPlugin from "./src/plugins/inject-components.mjs";

const __filename = fileURLToPath(import.meta.url);
const __dirname = path.dirname(__filename);

export default defineConfig({
  vite: {
    plugins: [mdInjectComponentsPlugin(path.resolve(__dirname, "./src/components/"))],
  },
});

[matthewp]

Going to close since this branch is fairly stale. Feel free to resubmit when you have it working.

[sylvinus]

FYI I probably won't have time to submit a more polished PR. It would be great if a more regular contributor could have a go at it!

[mrienstra]

@delucis, @matthewp, some months have passed and yay, Astro v2! Trying to figure out the status + next steps for this. Aside from rebasing + polishing this PR, maybe the RFC should be reviewed to make sure it's still in alignment with other goals & sufficiently clear?

Context:
RFC PR: withastro/roadmap#196
RFC: https://github.com/withastro/roadmap/blob/main/proposals/0022-frontmatter-plugins.md

The RFC has two unresolved questions, should those be addressed before someone picks up this PR?

(Coming here from #397 (comment))

[delucis]

Modifying frontmatter as proposed in this RFC is now available!

Some docs: https://docs.astro.build/en/guides/markdown-content/#modifying-frontmatter-programmatically

[mrienstra]

Nice, I hadn't seen that yet!

Associated issue: #5099
Associated PR: #5687
Bug fix (merged but not released): #5927

Builds on this foundation: #4176