fix(astro): server islands not working in prerendered pages with server output by matthewp · Pull Request #15767 · withastro/astro

matthewp · 2026-03-05T02:05:59Z

Changes

Fixes Astro v6 server islands not working with Node adapter #15753
A map is created in the manifest for server island names to their import paths. This was failing after splitting the build into ssr/prerender, because the map is created in ssr where islands might only be used in prerender pages.
Fix is to use a placeholder and update the mapping as a post-build hook after both builds are complete.

Testing

Added a new unit test in test/units/build/server-islands.test.js that runs an in-memory Astro build using virtual .astro modules (no fixture files on disk).
Test verifies the server island manifest is populated when server:defer is only used in prerendered pages.

Docs

N/A, bug fix

…er output (#15753)

changeset-bot · 2026-03-05T02:06:05Z

🦋 Changeset detected

Latest commit: 67d9150

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

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codspeed-hq · 2026-03-05T02:23:01Z

Merging this PR will not alter performance

✅ 18 untouched benchmarks

_{Comparing si-with-node (67d9150) with main (ca76ff1)¹}

No successful run was found on main (bc200b2) during the generation of this report, so ca76ff1 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

When server islands (server:defer) are only used in prerendered pages, the SSR build environment never discovers them — it leaves empty map placeholders in the manifest. The prerender build discovers the islands later but the SSR output is already finalized. Fix by deferring placeholder replacement during build: renderChunk leaves placeholders intact when no islands are known yet, renderChunk saves resolved filenames when processing them in the prerender env, and generateBundle patches the SSR manifest chunk in-memory. A post-build hook also patches the on-disk SSR output and copies island component chunks from the prerender directory to the server output.

pkg-pr-new · 2026-03-11T20:00:43Z

npm i https://pkg.pr.new/astro@15767

commit: ebcc350

louisescher · 2026-03-11T20:28:04Z

This fixed it for my site!

ematipico

That was a big one

This PR contains the following updates: | Package | Change | [Age](https://docs.renovatebot.com/merge-confidence/) | [Confidence](https://docs.renovatebot.com/merge-confidence/) | |---|---|---|---| | [astro](https://astro.build) ([source](https://github.com/withastro/astro/tree/HEAD/packages/astro)) | [`6.0.3` → `6.0.4`](https://renovatebot.com/diffs/npm/astro/6.0.3/6.0.4) | ![age](https://developer.mend.io/api/mc/badges/age/npm/astro/6.0.4?slim=true) | ![confidence](https://developer.mend.io/api/mc/badges/confidence/npm/astro/6.0.3/6.0.4?slim=true) | --- ### Release Notes <details> <summary>withastro/astro (astro)</summary> ### [`v6.0.4`](https://github.com/withastro/astro/blob/HEAD/packages/astro/CHANGELOG.md#604) [Compare Source](https://github.com/withastro/astro/compare/astro@6.0.3...astro@6.0.4) ##### Patch Changes - [#15870](withastro/astro#15870) [`920f10b`](withastro/astro@920f10b) Thanks [@matthewp](https://github.com/matthewp)! - Prebundle `astro/toolbar` in dev when custom dev toolbar apps are registered, preventing re-optimization reloads that can hide or break the toolbar. - [#15876](withastro/astro#15876) [`f47ac53`](withastro/astro@f47ac53) Thanks [@ematipico](https://github.com/ematipico)! - Fixes `redirectToDefaultLocale` producing a protocol-relative URL (`//locale`) instead of an absolute path (`/locale`) when `base` is `'/'`. - [#15767](withastro/astro#15767) [`e0042f7`](withastro/astro@e0042f7) Thanks [@matthewp](https://github.com/matthewp)! - Fixes server islands (`server:defer`) not working when only used in prerendered pages with `output: 'server'`. - [#15873](withastro/astro#15873) [`35841ed`](withastro/astro@35841ed) Thanks [@matthewp](https://github.com/matthewp)! - Fix a dev server bug where newly created pages could miss layout-imported CSS until restart. - [#15874](withastro/astro#15874) [`ce0669d`](withastro/astro@ce0669d) Thanks [@ematipico](https://github.com/ematipico)! - Fixes a warning when using `prefetchAll` - [#15754](withastro/astro#15754) [`58f1d63`](withastro/astro@58f1d63) Thanks [@rururux](https://github.com/rururux)! - Fixes a bug where a directory at the project root sharing the same name as a page route would cause the dev server to return a 404 instead of serving the page. - [#15869](withastro/astro#15869) [`76b3a5e`](withastro/astro@76b3a5e) Thanks [@matthewp](https://github.com/matthewp)! - Update the unknown file extension error hint to recommend `vite.resolve.noExternal`, which is the correct Vite 7 config key. </details> --- ### Configuration 📅 **Schedule**: Branch creation - At any time (no schedule defined), Automerge - At any time (no schedule defined). 🚦 **Automerge**: Disabled by config. Please merge this manually once you are satisfied. ♻ **Rebasing**: Whenever PR becomes conflicted, or you tick the rebase/retry checkbox. 🔕 **Ignore**: Close this PR and you won't be reminded about this update again. --- - [ ] If you want to rebase/retry this PR, check this box --- This PR has been generated by [Renovate Bot](https://github.com/renovatebot/renovate).  Co-authored-by: Renovate Bot <renovate@zarantonello.dev> Co-committed-by: Renovate Bot <renovate@zarantonello.dev>

fix(astro): server islands not working in prerendered pages with serv…

0e7da8b

…er output (#15753)

github-actions bot added the pkg: astro Related to the core `astro` package (scope) label Mar 5, 2026

Remove unnecessary fs import and dist cleanup from test

1912936

matthewp and others added 11 commits March 4, 2026 22:01

refactor server-island post-build patching into plugin hook

e8c8716

refactor: rename deferred server entries environment

073c8e0

fix: remove extra server-islands build environment

e3f33ba

chore: resolve lint ci unused exports and directives

3e49e84

Merge branch 'main' into si-with-node

35955c3

refactor: simplify server island map source generation

41c6dc6

refactor: share prerender output directory helper

0f6ebf4

Simplify changeset

8d0ac00

chore: restore benchmark template eslint directive

79661d2

test: allow either quote style in server-islands assertion

67d9150

matthewp added the pr preview Apply this label to a PR to generate a preview release label Mar 11, 2026

github-actions bot removed the pr preview Apply this label to a PR to generate a preview release label Mar 11, 2026

matthewp marked this pull request as ready for review March 11, 2026 20:38

Princesseuh approved these changes Mar 11, 2026

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ematipico approved these changes Mar 12, 2026

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matthewp merged commit e0042f7 into main Mar 12, 2026
27 checks passed

matthewp deleted the si-with-node branch March 12, 2026 12:05

astrobot-houston mentioned this pull request Mar 12, 2026

[ci] release #15858

Merged

CaiJimmy mentioned this pull request Mar 12, 2026

[v6 / Cloudflare] serverIslandMap?.get is not a function in pre-rendered page #15886

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fix(astro): server islands not working in prerendered pages with server output#15767

fix(astro): server islands not working in prerendered pages with server output#15767
matthewp merged 13 commits intomainfrom
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Merging this PR will not alter performance

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