Improve MDX glob perf - move Layout to async import

[bholmesdev]

Changes

• Resolves Slow DX with @astrojs/mdx 0.9.0 (not 0.8.1) #4307
• Moves frontmatter layout import to an async import

Wait, why an async import?

We found some interesting import.meta.glob behavior in the dev server after #4255 was introduced.

Scenario: a directory of MDX files use the same layout in their frontmatter. This layout includes an Astro.glob call for that same directory of MDX files. This is common when generating a "what to read next" section, navigation, etc.

• Before: When editing a single MDX file imported by the layout glob, only that file is re-transformed by Vite. All other globbed files will come from cache. This means near-instant dev server feedback (ignoring initial startup time).
• After: When editing a single MDX file imported by the layout glob, all globbed files are re-transformed by Vite. This could mean a 5-10 sec delay for every change in a project with 200ish MDX files.

I discovered that moving the frontmatter layout from an asynchronous import to a synchronous one introduced this issue. Recursion is to blame here: layout -> glob -> posts, which import -> layout -> glob -> posts, which import -> layout -> glob...

Testing

N/A

Docs

N/A

[changeset-bot]

🦋 Changeset detected

Latest commit: 8fc7469

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

This PR includes changesets to release 5 packages

Name	Type
@astrojs/mdx	Patch
@e2e/preact-component	Patch
@e2e/react-component	Patch
@e2e/solid-component	Patch
@e2e/svelte-component	Patch

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[FredKSchott]

LGTM with 1 comment to document