Upgrade tool v4 returns error

[rashthedude]

What version of Tailwind CSS are you using?
3.4.17

What build tool (or framework if it abstracts the build tool) are you using?

NextJS 15.1.4

What version of Node.js are you using?

v22.13.1

What browser are you using?

N/A

What operating system are you using?
macOS

Reproduction URL

N/A

Describe your issue

Running tailwindcss/upgrade@next returns this error:

│ Migrating JavaScript configuration files…

│ ↳ Could not load the configuration file: (0 , _deepmerge.default) is not a function

The tailwind config file contains a theme object that is a few levels deep.

[RobinMalfait]

Hey!

Can you share a minimal reproduction repo? It looks like some deepmerge library is being used somewhere, but hard to know what's up without looking at some code. Thanks!

[rashthedude]

Appreciate the swift response. After having commented out a good chunk of stuff in the tailwind config file, the upgrade tool ran successfully but reintroducing the commented bits crashes the app with the same error as above. I have reasons to suspect MUI package somehow is causing that. Not sure if you know anything about it?

[aidanCQ]

For me the 'presets` option was causing this issue. I was importing a sibling file as a preset. Remove the statement to fix