fix(vercel): strip trailing slash from prerendered route overrides

[thribhuvan003]

🔗 Linked issue

resolves #4392

❓ Type of change

• 📖 Documentation (updates to the documentation, readme, or JSdoc annotations)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality like performance)
• ✨ New feature (a non-breaking change that adds functionality)
• 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

prerendering a route with a trailing slash (e.g. /slash/) emits a Build Output override whose path keeps the slash — "slash/index.html": { "path": "slash/" } — and vercel doesn't match override paths like that, so the route falls through to the server function instead of being served statically (repro + live deploy in #4392).

this strips the trailing slash the same way the leading one is already stripped, so the override becomes "path": "slash". the root route is unaffected (/ still maps to ""). extended the vercel:web preset test with a prerendered /slash/ route.

the same line exists on the v2 branch (src/presets/vercel/utils.ts:166) — happy to open a backport if useful.

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.

[vercel]

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[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

Run ID: 28a71a89-f4cc-4de5-81bb-3ba850ebcf99

📥 Commits

Reviewing files that changed from the base of the PR and between eee0abd and 44908da.

📒 Files selected for processing (3)

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

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📝 Walkthrough

Walkthrough

This change updates Vercel prerender override path normalization to remove trailing slashes and adds regression coverage for a prerendered /slash/ route, including fixture setup and snapshot expectations for generated config and functions output.

Changes

Vercel override path handling

Layer / File(s)	Summary
Normalize override paths src/presets/vercel/utils.ts	Vercel prerender override path values now strip both leading and trailing slashes when build config overrides are generated.
Cover trailing-slash prerender route test/presets/vercel.test.ts, test/presets/fixtures/slash.ts	The Vercel preset test adds a /slash handler and prerenders /slash/, then updates snapshots to expect the normalized slash override and generated functions/slash.func entry.

Estimated code review effort: 2 (Simple) | ~10 minutes

Possibly related PRs

• nitrojs/nitro#4124: Also changes src/presets/vercel/utils.ts build config route and override generation logic for the Vercel preset.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title uses a conventional commit format and clearly describes the trailing-slash fix.
Description check	✅ Passed	The description matches the Vercel trailing-slash override bug and the added test coverage.
Linked Issues check	✅ Passed	The changes strip trailing slashes from Vercel override paths and add a regression test for /slash/.
Out of Scope Changes check	✅ Passed	The fixture and snapshot updates are directly tied to the reported bug and test coverage.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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