Latest Miniflare breaks SvelteKit build process on Pages

[ch-m-n]

What versions & operating system are you using?

miniflare@4.20250712.0

Please provide a link to a minimal reproduction

github.com/cloudflare/workers-sdk/tree/main/packages/miniflare

Describe the Bug

I just realize this issue is going on for last 3 days after months of successful building my app without any problem. SvelteKit run build completed but failed on wrap up of build process.

Please provide any relevant error logs

Expected output

17:06:18.111 ✨ Compiled Worker successfully 17:06:19.241 Found _routes.json in output directory. Uploading. 17:06:19.252 Validating asset output directory 17:06:21.963 Deploying your site to Cloudflare's global network... 17:06:24.982 Parsed 2 valid header rules. 17:06:26.305 Uploading... (28/57) 17:06:27.193 Uploading... (38/57) 17:06:27.288 Uploading... (47/57) 17:06:27.399 Uploading... (57/57) 17:06:27.400 ✨ Success! Uploaded 29 files (28 already uploaded) (1.50 sec) 17:06:27.400 17:06:27.786 ✨ Upload complete! 17:06:30.964 Success: Assets published! 17:06:35.213 Success: Your site was deployed!

Current situation

23:21:45.862 ✓ built in 24.59s 23:21:45.862 23:21:45.862 Run npm run preview to preview your production build locally. 23:21:45.863 23:21:45.863 > Using @sveltejs/adapter-auto 23:21:46.193 error during build: 23:21:46.193 ReferenceError: File is not defined 23:21:46.194 at Object.<anonymous> (/opt/buildhome/repo/node_modules/.pnpm/miniflare@4.20250712.0/node_modules/miniflare/dist/src/index.js:17017:3) 23:21:46.194 at Module._compile (node:internal/modules/cjs/loader:1256:14) 23:21:46.194 at Module._extensions..js (node:internal/modules/cjs/loader:1310:10) 23:21:46.194 at Module.load (node:internal/modules/cjs/loader:1119:32) 23:21:46.194 at Module._load (node:internal/modules/cjs/loader:960:12) 23:21:46.194 at Module.require (node:internal/modules/cjs/loader:1143:19) 23:21:46.195 at require (node:internal/modules/cjs/helpers:121:18) 23:21:46.195 at src/api/startDevWorker/MultiworkerRuntimeController.ts (/opt/buildhome/repo/node_modules/.pnpm/wrangler@4.25.0_@cloudflare+workers-types@4.20250719.0/node_modules/wrangler/wrangler-dist/cli.js:179927:26) 23:21:46.195 at __init (/opt/buildhome/repo/node_modules/.pnpm/wrangler@4.25.0_@cloudflare+workers-types@4.20250719.0/node_modules/wrangler/wrangler-dist/cli.js:9:59) 23:21:46.195 at src/dev.ts (/opt/buildhome/repo/node_modules/.pnpm/wrangler@4.25.0_@cloudflare+workers-types@4.20250719.0/node_modules/wrangler/wrangler-dist/cli.js:183416:5) 23:21:46.298  ELIFECYCLE  Command failed with exit code 1. 23:21:46.329 Failed: Error while executing user command. Exited with error code: 1 23:21:46.338 Failed: build command exited with code: 1 23:21:47.563 Failed: error occurred while running build command

[emily-shen]

Hi, would you be able to provide a minimal reproduction that demonstrates this issue so we can debug this? I've not been able to reproduce this with just a starter sveltekit template.

[zaibon]

I had the same issue since last Friday. I managed to resolve the problem by upgrading the "build system" from version 2 to version 3, in the settings.