Change frontmatter injection ordering

[bholmesdev]

Changes

• Resolves Empty Markdown frontmatter at build time #4429
• Resolves make parsed md/mdx frontmatter available to plugins #5099

Give remark and rehype plugins access to user frontmatter via frontmatter injection. This means data.astro.frontmatter is now the complete Markdown or MDX document's frontmatter, rather than an empty object.

This allows plugin authors to modify existing frontmatter, or compute new properties based on other properties. For example, say you want to compute a full image URL based on an imageSrc slug in your document frontmatter:

export function remarkInjectSocialImagePlugin() {
  return function (tree, file) {
    const { frontmatter } = file.data.astro;
    frontmatter.socialImageSrc = new URL(
      frontmatter.imageSrc,
      'https://my-blog.com/',
    ).pathname;
  }
}

Content Collections change

We have changed inject frontmatter to modify frontmatter in our docs to improve discoverability. This is based on support forum feedback where injection is rarely the term used.

To reflect this, the injectedFrontmatter property has been renamed to remarkPluginFrontmatter. This should clarify this plugin is still separate from the data export Content Collections expose today. We also expect remarkPluginFrontmatter to be deprecated once schemas can compute frontmatter based on file contents.

Testing

• Update frontmatter injection tests to consider frontmatter mutation

Docs

withastro/docs#2250

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[bholmesdev]

Move frontmatter injection utils to @astrojs/markdown-remark

[matthewp]

Blocking as we are not ready to merge major changes into main just yet.

[matthewp]

Code looks good! Let's talk about this with the core team before merging next week.

[aFuzzyBear]

It was interesting to see how you readjusted the order of the frontmatter process.
So its now safe to say that frontmatter is mutable via the remark tree and the output of that is what is then provided into other contexts

[aFuzzyBear]

💚 this

[matthewp]

Approved by TSC, @bholmesdev just need to fix the conflicts.

[andersk]

It seems frontmatter needed to be added here where _internal was removed.

• fix: undefined remarkPluginFrontmatter after calling render method #5927