[POC] Eject feature

[banyan]

Hi! I want to pursue a possibility that if we can have eject feature in webpacker.

I understand webpacker can configure all of webpack settings using ConfigList and ConfigObject. If a use case is just simple, then we can go with webpacker without having many custom settings, but if we want to customize, eventually we have to understand internal webpacker codes. In that case, I think webpacker:eject would be useful especially who knows webpack well and wants to configure directly.

I believe webpacker:eject would be an escape route of a tall mountain. Even it might not be used, it will make people feel easy and it will strengthen webpacker. That being said, this PR is just POC and has a problem how to maintain the initial webpack.config.js. IMO, webpack.config.js is not need to be completely compatible with webpacker's one, but just core logic is enough.

eject will do following things:

• Generete webpacker compatible webpack.config.js while referring to config/webpacker.yml's settings.
  • config/webpack/loaders/* will be used from generated webpack.config.js. so for example, if you run bundle exec rake webpacker:install:elm before, you can still use elm.
• webpacker gem will have remained for asset helpers like javascript_pack_tag.
• npm-scripts yarn start and yarn build will be added.

This PR works well with fresh rails new projects.

I'm happy if I can get any feedbacks.
@gauravtiwari I saw this. do you have any idea regarding implementation?

[jakeNiemiec]

You beat me to it 😆, I had been working out an eject function for a while. I stopped because I felt like there needs to be a completely separate gem for resolving entry files/chunks from javascript_pack_tags.

Looks good!

[nikushi]

Very interesting work. FYI, I made WebpackManifest gem a while ago, which provides helpers to resolve path and chunk.

[h0jeZvgoxFepBQ2C]

Anyone knows if this PR will get merged?

[derekblank]

@banyan Updating lines 2, 10, 12, 14, and 33 of template.rb to use double-quoted strings will resolve the build failure.

[trcarden]

Does this have support broadly from the rest of the rails team? Seems like an excellent idea and I would even say that if webpacker was just reconstructed into a set of generators it may be even better. We have to learn parts of webpack anyway and in order to know why our CSS is showing up inline instead of a file in dev you have to dive into webpacker to determine the config anyway.
See: #2161

[kimihito]

@banyan has extracted this PR as webpacker_ejetor gem 🎉