PR #73: vercel-functions: skip default-export rule for App Router pages

• Repository: vercel/vercel-plugin
• Author: mvanhorn
• State: open | merged: False
• Link: https://github.com/vercel/vercel-plugin/pull/73

Description (problem / solution / changelog)

Fixes the false-positive Use named exports (GET, POST, PUT, DELETE) instead of default export for route handlers ERROR that fires on every page.tsx, layout.tsx, loading.tsx, error.tsx, not-found.tsx, sitemap.ts, and template.tsx in a Next.js App Router project.

Refs anthropics/claude-code#54989 (the bug was reported in claude-code, but the validation rule lives here in skills/vercel-functions/SKILL.md lines 25-29).

Problem

The current rule:

validate:
  -
    pattern: export\s+default\s+function
    message: 'Use named exports (GET, POST, PUT, DELETE) instead of default export for route handlers'
    severity: error

matches any default-exported function. Next.js App Router requires default exports for page.tsx, layout.tsx, loading.tsx, error.tsx, not-found.tsx, sitemap.ts, and template.tsx, so the rule fires [ERROR] on every Write/Edit to any of those files. The reporter has a 44-page project where this fires constantly and cannot be suppressed without disabling the entire skill.

Fix

Add a skipIfFileContains regex (the same shape used in skills/routing-middleware/SKILL.md) that suppresses the rule when the file shows strong signals of being an App Router file rather than a route handler:

Each of these is overwhelmingly common in App Router pages and overwhelmingly absent from route handlers. A buggy export default function handler inside a route.ts still fires the rule because none of the patterns match.

Why skipIfFileContains and not a new field

The reporter suggested onlyIfFilename / skipIfFilename. Adding a new schema field requires the downstream consumer (claude-code) to honor it, otherwise the field is inert and the false positive remains. skipIfFileContains is already supported and already used by skills/routing-middleware/SKILL.md, so this PR fixes the bug today without coordinating new field support.

Verification

Tested the regex against representative content for each affected file plus the buggy route handler case (Python regex used for portability):

page.tsx (server)                          fires=True  skip=True  -> skipped (correct)
page.tsx (client - 'use client')           fires=True  skip=True  -> skipped (correct)
layout.tsx (RootLayout)                    fires=True  skip=True  -> skipped (correct)
layout.tsx (MarketingLayout)               fires=True  skip=True  -> skipped (correct)
sitemap.ts                                 fires=True  skip=True  -> skipped (correct)
loading.tsx                                fires=True  skip=True  -> skipped (correct)
not-found.tsx                              fires=True  skip=True  -> skipped (correct)
route.ts (BUG: export default fn handler)  fires=True  skip=False -> flagged (correct)
route.ts (BUG: export default with NextResponse) fires=True  skip=False -> flagged (correct)

Plugin-level checks still pass:

$ bun run validate
PASSED with 1 warning(s)

$ bun run build
build:skills — 0 updated, 10 unchanged, 0 errors
build:from-skills — 0 updated, 8 unchanged, 0 errors

Changed files

• generated/build-from-skills.manifest.json (modified, +1/-1)
• generated/skill-manifest.json (modified, +3/-2)
• skills/vercel-functions/SKILL.md (modified, +7/-0)