Slow-starting workers give a confusing error message when source maps are enabled #9985
Description
What versions & operating system are you using?
Wrangler 4.22.0
Please provide a link to a minimal reproduction
No response
Describe the Bug
Forked this issue from #9818.
When a worker’s startup time is too long and upload_source_maps is enabled in wrangler.json, running wrangler deploy gives the following error (found in the full logs):
--- 2025-07-16T13:48:34.386Z error
�[31m✘ �[41;31m[�[41;97mERROR�[41;31m]�[0m �[1mUnable to determine module type for application/source-map mime type�[0m
---
--- 2025-07-16T13:48:34.386Z debug
Error: Unable to determine module type for application/source-map mime type
at getModuleType (/workspaces/dev/node_modules/.pnpm/[email protected]_@[email protected]/node_modules/wrangler/wrangler-dist/cli.js:152517:13)
at /workspaces/dev/node_modules/.pnpm/[email protected]_@[email protected]/node_modules/wrangler/wrangler-dist/cli.js:152530:13
at Array.map (<anonymous>)
at convertWorkerBundleToModules (/workspaces/dev/node_modules/.pnpm/[email protected]_@[email protected]/node_modules/wrangler/wrangler-dist/cli.js:152529:33)
at analyseBundle (/workspaces/dev/node_modules/.pnpm/[email protected]_@[email protected]/node_modules/wrangler/wrangler-dist/cli.js:152583:16)
at handleStartupError (/workspaces/dev/node_modules/.pnpm/[email protected]_@[email protected]/node_modules/wrangler/wrangler-dist/cli.js:152630:28)
at helpIfErrorIsSizeOrScriptStartup (/workspaces/dev/node_modules/.pnpm/[email protected]_@[email protected]/node_modules/wrangler/wrangler-dist/cli.js:152650:11)
at deploy (/workspaces/dev/node_modules/.pnpm/[email protected]_@[email protected]/node_modules/wrangler/wrangler-dist/cli.js:153208:15)
at process.processTicksAndRejections (node:internal/process/task_queues:105:5)
at async Object.handler (/workspaces/dev/node_modules/.pnpm/[email protected]_@[email protected]/node_modules/wrangler/wrangler-dist/cli.js:118671:62)
---
As @petebacondarwin noted, this is because the bundle analyser used in startup timeout diagnosis can’t handle source maps. Disabling upload_source_maps fixes this and gives the appropriate error message.
(FWIW, I’m mostly raising this issue so future users find it and it saves them a headache trying to figure out what the error is about; no expectation to really fix it)
Please provide any relevant error logs
No response