Introduce a way for extending Webpack configurations

[halfzebra]

We have a few PRs introducing new configuration flags.

I'm afraid this is not the most user-friendly way to introduce some options in terms of configuration.

I'm proposing to remove the configuration flags, such as DEAD_CODE_ELIMINATION and stop using env variables for configuration(this might be a impossible to avoid in some cases, but the usage could be minimized)

Proposal

Create Elm App should allow the extension or modification of the Webpack configuration in a similar way to storybook.

Workflow

1. Create .elmapp folder
2. Add webpack.config.prod.js
3. The rest of the functionality is described here: https://storybook.js.org/configurations/custom-webpack-config/

Potential

Make easier to address #246 #254

Target auditory

People who know Webpack, e.g. to address
#263 by @cdaringe
#262 by @tzemanovic

Please leave a comment on this issue if you have an opinion.

Further development

I'm thinking about introducing .elmapprc to address #160 and #255, the idea above might be or might not be a power-user tool to cover some edge-cases.

.elmapprc could introduce some high-level overrides, such as changing the output directory and other stuff similar to vue-cli.

Please share your thoughts if you have time and opinions on this @fobos @gyzerok @jackfranklin

[cdaringe]

Whatever works. I like the idea of being able to provide a function to modify it.

[tzemanovic]

This sounds great. I was thinking the same thing about the env vars when I opened #262 and since then I actually needed to add another custom config, so I would very much welcome this change.

[halfzebra]

Leaving this for a reference, here is a similar proposal for Create React App.

[halfzebra]

Vue Cli has a pretty good approach for Working with Webpack, it enables the extension and modification of the pre-packaged configuration from the config file.

As I have mentioned before, introducing a custom config file would make sense, because it seems like a future-proof way of introducing extendability.

[tzemanovic]

Do you have any preference so far? Vue's approach looks quite powerful, but their internal webpack config is done with webpack-chain. I'd be happy to keep it simple by being able to provide my own prod config file with overrides like in the storybook, which seems like much less hassle, but I have no experience dealing with either of these.

[halfzebra]

Currently, I'm not considering using webpack-chain, because it's another layer of complexity for an API that is intended for confident Webpack users.

Plain Webpack config might be hard to work with, but it's the good old Webpack config instead of a new API to represent it.

Please let me know if that sounds reasonable 🙂

[tzemanovic]

That was my thinking when I looked at webpack-chain 👍