[DenisCDev]

Changes

• astro sync (also run by astro check and astro build) creates a temporary Vite server with optimizeDeps: { noDiscovery: true }. Astro itself (dev toolbar deps) and integrations such as @astrojs/react and @astrojs/preact add optimizeDeps.include entries, so Vite still runs the dependency optimizer on that server. It wrote to the project's default Vite cache, node_modules/.vite, which is the cache a running astro dev reads from. The dev server's optimized dependencies were replaced with ones built by the temporary server, for example React's production jsx-dev-runtime where jsxDEV is undefined, and islands broke with _jsxDEV is not a function or Invalid hook call until the dev server was restarted with --force.
• The temporary server now uses its own Vite cacheDir, <cacheDir>/vite-sync/ under Astro's cacheDir. It optimizes the same dependencies as before and plugins see the same config; only where the output is written changes.

Fixes #18449

Testing

• Added a test to test/astro-sync.test.ts. It writes a placeholder node_modules/.vite/deps/_metadata.json (standing in for a running dev server's cache) into a fixture that no other test starts a dev server on, runs sync, and asserts the file is unchanged. Without the change in sync/index.ts it fails, because sync replaces the placeholder with its own optimizer metadata. With the change, pnpm -C packages/astro exec astro-scripts test "test/astro-sync.test.ts" passes 10/10.
• Checked the same change against the reproduction from Running astro sync/check/build while astro dev is running breaks React islands in the dev server #18449 (astro 7.4.0 + @astrojs/react): with astro dev running, node_modules/.vite/deps is no longer modified by astro sync, astro check or astro build, and sync's output goes to node_modules/.astro/vite-sync/deps.

Docs

No docs change. There is no API or config change; the only visible effect is a vite-sync directory inside Astro's cacheDir.

[changeset-bot]

🦋 Changeset detected

Latest commit: e873dff

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

This PR includes changesets to release 1 package

Name	Type
astro	Patch

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Click here if you're a maintainer who wants to add another changeset to this PR

[codspeed]

Merging this PR will not alter performance

⚠️ 3 benchmarks spent significant time in system calls

System calls cannot be consistently instrumented, so they are not included in the measure, which understates the real cost. Please switch to the Walltime instrument to accurately measure system calls.

Measurement and system calls

• Build: full server site
• Build: hybrid site (static + server)
• Build: full static site

ℹ️ 13 benchmarks have no flame graph

The flamegraph could not be generated because too much time was spent in runtime internals, making the visualization not useful for performance analysis.

• Build: full server site
• many-components (markHTMLString, isHTMLString, validateProps)
• large-array (BufferedRenderer per child)
• many-head-elements (head dedup)
• many-slots (eager slot prerendering)
• large-array [streaming]
• head-propagation-1000 (propagator collection)
• many-expressions (renderChild dispatch, escapeHTML)
• static-heavy (markHTMLString baseline)
• head-propagation-2000 [streaming]
• …and 3 more

✅ 21 untouched benchmarks

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_{Comparing DenisCDev:fix/sync-separate-vite-cache (e873dff) with main (70834bb)¹}

Footnotes

1. No successful run was found on main (c55134c) during the generation of this report, so 70834bb was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

[astro-factory]

Verdict: approved. No blocking findings remain.

Findings

No findings.

Merge Requirement Assessment

Status: satisfied

• The temporary Vite server used by astro sync, astro check and astro build must not write optimized dependencies into the cache a running astro dev reads (#18449). createTempViteServer now passes cacheDir: fileURLToPath(new URL('./vite-sync/', settings.config.cacheDir)) in the command config (packages/astro/src/core/sync/index.ts:260). createVite merges this config last (create-vite.ts:370), so it overrides two other values: Astro's default node_modules/.vite/ and any user-set vite.cacheDir. The relative schema always resolves config.cacheDir to a directory URL ending in /, so the new URL call reliably resolves to a subdirectory. All three commands reach this server through syncInternal whenever content sync is not skipped.
• Plugins should see the same config and optimize the same dependencies; only the output location changes. optimizeDeps, ssr and the plugin pipeline are unchanged, and the diff only adds cacheDir.
• Regression coverage. The new test in test/astro-sync.test.ts writes a placeholder node_modules/.vite/deps/_metadata.json, runs sync and asserts the file is unchanged. Without the change, sync's optimizer output would overwrite the placeholder and the assertion would fail. The test cleans up in finally. Its fixture has its own cacheDir and outDir, and other tests don't start a dev server on it.

Review Status

Verdict: ready to merge based on static review
Context: PR #18451, plus the linked issue #18449 as described in the PR body
Scope: PR base c55134c1 to head e873dff3 (3 files: sync/index.ts, astro-sync.test.ts, and the changeset).
Changeset: present and covers astro (patch).
Limitations: The linked issue was not fetched separately; requirements came from the PR description.
Validation: Static review only; no project code, tests, builds, or checks were run.
GitHub context: collected
Git scope: PR base/head verified

This review was made by an LLM. The analysis may be wrong, and reports might be incorrect.

[matthewp]

I'm a little unsure about this but think we can merge this version and see what happens. The downside to using a different cache directory for sync is that you lose cache-warming when sync runs first, but I don't think that's the common case anyways.