It turns out that this is not unique to ESM. I've created a minimally reproducible example that has two files for defining colors: colors-1.json and colors-2.json. When running npm run tokens (which calls Style Dictionary), the CSS file is generated correctly, but the following warning is logged:

Token collisions detected (1):

Collision detected at: colors! Original value: color, New value: color

I did some investigating, and it's a result of the "$type": "color" property being used in both files. Removing it in one or both files resolves the logging issue.

Given that $type is not a token definition, I would not expect for a "collision" to be detected.

Hope this helps! I'm happy to open an issue and contribute a fix if you agree this is worth addressing.

Ah yes that's most certainly a bug, I'm surprised it's the first time I'm seeing it. Feel free to raise an issue, if you wanna take a stab at a fix that would be much appreciated! I suspect the issue to be somewhere in the deepExtend/combineJSON utilities

Issue created: #1316