npm run dev fails with EPERM error on WIndows

[terrygonguet]

After tinkering a bit with a new Keystone 6 project, the npm run dev command started failing with the following error:

Error: EPERM: operation not permitted, rename 'C:\Users\...\node_modules\.prisma\client\query_engine-windows.dll.node.tmp34132' -> 'C:\Users\...\node_modules\.prisma\client\query_engine-windows.dll.node'
    at async Object.rename (node:internal/fs/promises:782:10)
    at async overwriteFile (C:\Users\...\node_modules\@prisma\client\generator-build\index.js:4477:5)
    at async generateClient (C:\Users\...\node_modules\@prisma\client\generator-build\index.js:10035:7)
    at async LineStream.<anonymous> (C:\Users\...\node_modules\@prisma\client\generator-build\index.js:4380:24

It looks like this happens if I import ".prisma/client" in keystone.ts (I wanted to export a context object to be used by a frontend app). It also seems to make starting the dev server quite a lot slower.

This error does not happen if I run the project within WSL.

• Node v24.13.1
• NPM 11.8.0
• @keystone-6/auth 8.1.0
• @keystone-6/core 6.5.1

I fixed it by putting the code to build and export the context object in its own file but the error stumped me for quite a while. Maybe you could detect it ahead of time and warn users to not do that?

[dcousens]

Difficult to say exactly what is happening here, but I think opting for WSL is probably a better option when working with dependencies like prisma and their native binaries.

[terrygonguet]

I assume that because the keystone.ts file is imported first, to compute the schema, the prisma client is using the generated engine when it's trying to rebuild it. No idea why it's not a problem in WSL 🤷🏻

As I said, it's not really a problem, the solution is just to import .prisma/client in a file that won't be imported from keystone.ts and it's good.

I'm mostly reporting it in hopes that it could be detected by Keystone and you could warn the user of what to do. Otherwise the dev server seemingly randomly breaks with a completely unrelated error that is quite hard to debug (even LLMs had no idea what could possibly be happening, recommending random solutions).

Either fail early if you detect an import during the dev server, or recognize the error during the prisma rebuild and show a better error message.

[dcousens]

Fair, I don't have a Windows environment with which to test this, is this something you'd be willing to work on?

[terrygonguet]

I may be able next week, I'll try to show a slightly better error.