Can't modify Markdown frontmatter from remark plugin

[rgov]

What version of astro are you using?

2.8.3

Are you using an SSR adapter? If so, which one?

none

What package manager are you using?

nom

What operating system are you using?

macOS Ventura

What browser are you using?

Safari

Describe the Bug

The example given for modifying Markdown frontmatter programmatically doesn't seem to work.

Following exactly that example, I can see (with console.log()) that my plugin is being called. But in one of my .astro files I inspect the data objects for each post, and the inserted field is not present.

(Question: Is there any difference between the markdown and mdx sections of the config file? The documentation seems ambivalent about which to use. I've tried both.)

What's the expected result?

The example should add the customProperty to the front matter.

Link to Minimal Reproducible Example

https://stackblitz.com/edit/github-klm8sa?file=example-remark-plugin.mjs

Participation

• I am willing to submit a pull request for this issue.

[rgov]

withastro/astro#5687 says,

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.

The renaming does not clarify things for me. What else does modifying the frontmatter affect? I suppose it could change an MDX file's { frontmatter.customProperty }, but I'm not sure what the use case would be.

---

Edit: I see, this separate part of the documentation is more clarifying. The plugin only runs at render time.

[Princesseuh]

Transferring to docs since it seems like this was mostly a misunderstanding of the docs regarding when remark plugins affect the frontmatter

[delucis]

Thanks for transferring @Princesseuh.

The guidance in the Markdown guide works well when NOT using content collections, but we should add a link to the content collections version to make the difference clearer.

[TheOtterlord]

Fixed in #3988