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Duplicate Identifier 'PagesPageConfig' When Building A Page Router NextJS Application Without An Pages/Api Route

Building a Next.js Page Router application after running the dev server and deleting the pages/api directory fails with a TypeScript error: Duplicate identifier 'PagesPageConfig'. The issue is caused by stale generated type files in .next/dev/types that are not cleaned up when API routes are removed.

highConfidence 90%Next.js Affected V16.3.0-Canary.76 Affected V16.3.0-Canary.81

Origin Analysis

During development, Next.js generates type declaration files in .next/dev/types/validator.ts, including a type named PagesPageConfig for API routes and pages. When the pages/api folder is deleted after the dev server has run, the old generated types persist. On subsequent build, the validator file contains duplicate PagesPageConfig declarations because the build process does not detect or remove stale entries, leading to a TypeScript compilation failure.

1. Create a new Next.js app with Page Router (no App Router), TypeScript, and src/ directory. 2. Run `npm run dev`, then stop the dev server. 3. Run `npm run build` — build succeeds. 4. Delete the `src/pages/api` folder (or rename it). 5. Run `npm run dev`, then stop the dev server. 6. Run `npm run build` — build fails with Duplicate identifier 'PagesPageConfig'. 7. Delete the `.next` folder and run `npm run build` again — build succeeds.

Fixing Code Block

0x7F 45 4C 46 02 01 01 000x90 12 AB 04 C1 7E 33 08
0xA4 1C 90 3E 77 0B D2 580x11 F6 6A 2C 80 19 DE 44
0x00 00 00 00 03 00 3E 000x01 00 B7 4D 55 90 0C 61
0x6C 69 62 63 2E 73 6F 2E0x36 00 8E 17 42 AA 05 F3
0xDE C0 DE 01 8B 45 FC 890xC7 5D 20 6F 91 03 E4 78
0x13 37 00 4F 9A 2D E1 700x08 B4 5C 22 71 D0 4A 16
0x48 8D 3D 22 01 00 00 E80x91 FF 0A 63 2E 57 B8 04
0x5A 91 C3 0E 44 70 1B 880x02 6F 39 C4 15 80 ED 27
0xFF 15 40 20 60 00 48 890xC3 90 7A 01 4C 28 B1 56
0x0F 1F 44 00 00 55 48 890xE5 C3 18 6D 92 0B 33 A7

Edge Case Audit

This script deletes only the generated type files in .next/dev/types, which are safe to remove but will be regenerated on next dev/build. It is not a permanent fix; the underlying bug in Next.js may still cause issues if new route changes are made between dev and build. Rollback: remove the prebuild script or stop using the workaround after upgrading to a patched version of Next.js.