Regression in frontmatter accessible to remark plugins in Astro 5 + Content Layer

[HiDeoo]

Astro Info

Astro                    v5.0.9
Node                     v18.20.3
System                   Linux (x64)
Package Manager          npm
Output                   static
Adapter                  none
Integrations             @astrojs/mdx

If this issue only occurs in one browser, which browser is a problem?

No response

Describe the Bug

When using Astro v5 with Content Layer, there is a regression in the frontmatter accessible to remark plugins that is no longer the user-defined frontmatter but the frontmatter validated by the collection schema.

Using the following collection definition with a schema only allowing a title property and using a transform to add an someOtherField additional field:

const docs = defineCollection({
  loader: glob({ pattern: "**/*.{md,mdx}", base: "./src/content/Docs" }),
  schema: z
    .object({
      title: z.string(),
    })
    .transform((data) => ({
      ...data,
      someOtherField: "Added by transform",
    })),
});

And the following markdown file:

---
title: Test Mardown
foo: bar
---

Hello from Markdown!

A remark plugin accessing file.data.astro?.frontmatter will get the following object:

{ title: 'Test Mardown', someOtherField: 'Added by transform' }

Using an MDX file with the same content or Astro v4, the object would be:

{ title: 'Test MDX', foo: 'bar' }

Additional notes:

• May need to run npm run dev -- --force in StackBlitz to see the logs
• Here is a link to the same setup in Astro v4: https://stackblitz.com/edit/github-w2juvll6-fxyvazic?file=astro.config.mjs

What's the expected result?

The expected result should be the same as Astro v4 and be consistent between markdown and MDX files:

{ title: 'Test MDX', foo: 'bar' }

Link to Minimal Reproducible Example

https://stackblitz.com/edit/github-w2juvll6?file=astro.config.mjs

Participation

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

[ascorbic]

Thanks for the repro! Turns out it was a simple fix.