Custom builder and --why

Running size-limit on react-dropzone throws an error:

$ size-limit --why
 ERROR  Error: 
ERROR in ./src/index.js
Module parse failed: /Users/okonet/Projects/OSS/react-dropzone/src/index.js Unexpected token (266:17)
You may need an appropriate loader to handle this file type.
|   }
| 
|   renderChildren = (children, isDragActive, isDragAccept, isDragReject) => {
|     if (typeof children === 'function') {
|       return children({
 @ multi ./src/index.js
    at runWebpack.then.stats (/Users/okonet/Projects/OSS/react-dropzone/node_modules/size-limit/index.js:150:15)
    at <anonymous>
error Command failed with exit code 1.
info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.

Looking at code I could not find babel-loader. Is this project suppose to only be used with ES5 code?

[asotog]

I have same issue, my project’s javascripts are using spread operator and is throwing error

Module parse failed: /Users/alejandrosoto/Downloads/github-repos/crafter-social-rui/src/js/main.js Unexpected token (8:25)
You may need an appropriate loader to handle this file type.

[ai]

Size Limit 2.0 was released with modular architecture. Now we have a better UI to explain that --why will not work for a custom builder.