Attempting to show off a potential bug in how rollup handles different types of configurations with the sideEffects field in package.json

Rollup build with sideEffects: ['*.css']

Rollup build with sideEffects: undefined

Setup

• yarn install
• yarn start
• open http://localhost:8888/
• notice that there is not CSS included from @adobe/react-spectrum

Getting CSS to be included

A few different changes are required to get the CSS to be bundled.

Each package.json needs to have sideEffects: true or sideEffects: undefined instead of sideEffects: ['*.css'] to make it easy to demonstrate run the following commands

• yarn install
• yarn mutate-modules
• yarn start

After waiting for a successful build open http://localhost:8888/ and see that CSS was included

restoring mutated modules

• yarn fix