fix(cloudflare): add namespace filter to astro-frontmatter-scan esbuild plugin

[barry3406]

Fixes #16203

Problem

The astro-frontmatter-scan esbuild plugin registers its onLoad handler without a namespace filter. In esbuild, an unfiltered onLoad matches all namespaces, including html. When a .ts file default-imports an .astro component, Vite's dep scanner resolves the .astro file into the html namespace. The plugin intercepts it and returns only the extracted frontmatter — which has no export default — causing:

[ERROR] No matching export in "html:/path/to/Component.astro" for import "default"

Fix

Add namespace: 'file' to the onLoad call so the plugin only handles .astro files resolved from the filesystem. Files in the html namespace now fall through to Vite's built-in htmlTypeOnLoadCallback, which already appends export default {} for non-.vue files.

Test plan

• Verified against the reproduction repo from the issue: error no longer occurs
• file namespace behavior is unchanged — same handler, same logic, only the namespace scope is narrowed

[changeset-bot]

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Latest commit: 80e3e01

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[barry3406]

Hey @ematipico, could you take a peek at this when you get a chance? It's a small fix for a Cloudflare adapter regression where astro-frontmatter-scan was matching the html namespace by accident. Happy to adjust anything if needed.

[rururux]

Hi! Could you please add a changeset and some tests to verify the fix?
These will be needed for the PR to be merged. Thanks!

[barry3406]

Hey @rururux — done! Pushed:

• .changeset/fix-cf-frontmatter-scan-html-namespace.md (@astrojs/cloudflare: patch)
• packages/integrations/cloudflare/test/esbuild-plugin-astro-frontmatter.test.js with four cases:
  1. Asserts every onLoad handler the plugin registers declares namespace: "file" — the actual regression guard for [Bug]: astro-frontmatter-scan esbuild plugin missing namespace filter causes "No matching export" errors during dep scan #16203
  2. Frontmatter is extracted correctly when invoked in the file namespace
  3. Empty frontmatter falls back to empty contents
  4. Top-level return → throw rewrite still works

I verified the regression assertion fails when the namespace: "file" filter is removed and passes once it's back. Went with a unit test for speed, but if you'd rather see this as a full integration fixture instead, happy to swap it out. Thanks for the review!

[rururux]

Thanks for adding the changeset!
It looks a bit technical, so could you please make it more concise?
You can refer to this link for some guidance: https://contribute.docs.astro.build/docs-for-code-changes/changesets/

[barry3406]

Done — shortened the changeset to one user-facing line per the docs guide. Thanks!

[barry3406]

Thanks @rururux — read the changesets guide properly this time and force-pushed a revised version that drops the implementation note and follows the lived Fixes X failing with Y when Z pattern from fix-svelte-prerender-node.md. Let me know if it's still off and I'll keep trimming.

[rururux]

Thanks! The changeset looks good now.
Regarding the tests, I personally think it might be better to add an integration test rather than a unit test, similar to the existing ones.
This is because the current test doesn't seem to verify if the No matching export in 'html:...' for import 'default' message is actually resolved by these changes.

[barry3406]

Thanks @rururux — converted to an integration test in test/ts-astro-import.test.js. The fixture mirrors the structure from the issue reproduction repo: a lib/ui.ts that default-imports Inner.astro and Outer.astro (where Outer wraps Inner), consumed by a page. It runs through loadFixture and fixture.build(), modelled on top-level-return.test.js.

The test captures the Astro logger output and asserts that neither No matching export in "html:..." for import "default" nor Failed to run dependency scan appears during the build.

I verified the regression actually fires: with namespace: 'file' removed from the plugin, both assertions fail with the exact error from #16203. Dropped the old unit test in the same commit. Let me know if the fixture or assertions need adjusting!