@next/swc is not a development dependency (blowing Heroku slug size)

What version of Next.js are you using?

12.0.7

What version of Node.js are you using?

14.15.4

What browser are you using?

Chrome

What operating system are you using?

Linux

How are you deploying your application?

Heroku

Describe the Bug

Heroku limits the compressed size of the app folder to 500 MB. Somehow, the total compressed size of the app went from 200 to 600, after upgrading from Next 11 to 12.

After investigating the problem, the issue is that somehow, all the binaries for SWC are included in the build and not removed when running npm prune.

$ du -ha --max-depth 3 /app | sort -hr | grep @next
481M	/app/node_modules/@next
48M	/app/node_modules/@next/swc-linux-x64-gnu
48M	/app/node_modules/@next/swc-android-arm64
47M	/app/node_modules/@next/swc-linux-x64-musl
47M	/app/node_modules/@next/swc-linux-arm64-musl
47M	/app/node_modules/@next/swc-linux-arm64-gnu
47M	/app/node_modules/@next/swc-linux-arm-gnueabihf
44M	/app/node_modules/@next/swc-win32-x64-msvc
40M	/app/node_modules/@next/swc-win32-arm64-msvc
40M	/app/node_modules/@next/swc-darwin-x64
38M	/app/node_modules/@next/swc-win32-ia32-msvc
38M	/app/node_modules/@next/swc-darwin-arm64
1.8M	/app/node_modules/@next/react-dev-overlay
68K	/app/node_modules/@next/react-refresh-utils
32K	/app/node_modules/@next/env
28K	/app/node_modules/@next/polyfill-module
....

The actual problem is that because those are binaries, they barely compress, so they really break the slug size limit of heroku.

Expected Behavior

Given that the build was already completed, I imagine it is unnecessary to have this packages in production. We should allow these packages to be removed by npm prune.

To Reproduce

Deploy any Next 12 app to Heroku.

[carlosbaraza]

For Heroku and NextJS 12.0.7, I had to add the following custom Heroku build steps to package.json:

Disable SWC compiler because of #31855

"heroku-postbuild": "echo '{\"presets\": [\"next/babel\"]}' > .babelrc && npm run build",

Remove SWC and .next/cache to reduce the slug size:

"heroku-cleanup": "rm -rf .next/cache && find node_modules/@next -depth -maxdepth 1 -type d -name 'swc*' -exec rm -rf {} \\; -prune #Remove cache and SWC binaries to reduce heroku slug size",

Hope this workaround helps someone.

[github-actions[bot]]

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