fix(nitro): vercel function rules - preserve relative symlinks

[AndrewBarba]

Summary

• preserve relative symlink targets when Vercel functionRules copies the traced server function
• add a regression using Nitro’s existing multi-version nf3 fixture

Context

nf3 emits relative links from package locations into node_modules/.nf3. Node’s fs.cp resolves those links by default, so copying __server.func into a route-specific function rewrites them to absolute paths in the temporary build directory. Once that directory is removed, the deployed function contains dangling dependency links.

Using verbatimSymlinks: true keeps the traced dependency graph self-contained in each copied function directory.

Related downstream report and workaround: vercel/eve#1279

Testing

• regression confirmed failing before the fix and passing afterward
• pnpm fmt
• pnpm typecheck
• pnpm vitest run test/presets/vercel.test.ts — 139 passed, 2 skipped, 2 todo
• full suite attempted with TZ=UTC pnpm test; the Rollup run reached 1,025 passing tests and stopped on an unrelated Vite HMR assertion receiving two identical full-reload events instead of one

[vercel]

@AndrewBarba is attempting to deploy a commit to the Nitro Team on Vercel.

A member of the Team first needs to authorize it.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: d3ceb175-57dd-47de-a860-35f0908f6bf9

📥 Commits

Reviewing files that changed from the base of the PR and between 77b77ff and b90cd1b.

📒 Files selected for processing (2)

• src/presets/vercel/utils.ts
• test/presets/vercel.test.ts

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📝 Walkthrough

Walkthrough

The Vercel preset now preserves symlink targets when copying custom function directories. The web preset test compares the nitro-lib symlink targets in generated server and route function directories.

Changes

Vercel symlink preservation

Layer / File(s)	Summary
Preserve and verify dependency symlinks src/presets/vercel/utils.ts, test/presets/vercel.test.ts	The function directory copy enables verbatimSymlinks, and the web preset test verifies matching nitro-lib symlink targets.

Estimated code review effort: 1 (Trivial) | ~5 minutes

Possibly related issues

• vercel preset: functionRules forces full bundle copy per route, blowing up output size #4233 — Both changes modify Vercel function-copy behavior related to preserving symlink targets.

Possibly related PRs

• nitrojs/nitro#4124: Both modify Vercel custom function directory generation.
• nitrojs/nitro#4373: Both modify copy semantics in createFunctionDirWithCustomConfig, including symlink handling.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title follows conventional commits and clearly describes the Vercel symlink preservation change.
Description check	✅ Passed	The description is directly related to preserving Vercel function symlinks and the added regression test.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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commit: b90cd1b