feat #323: Allow fn & promise from webpack config

[third774]

PR for #323

[ashleygwilliams]

@xtuc can you please review this PR?

[xtuc]

Could you please add the env and argv params from the doc https://webpack.js.org/configuration/configuration-types/#exporting-a-function?

Also, It seems to me that we are duplicating the webpack-cli logic. Do you know if there a way to share some logic/code? We are fine having it as dependecy.

[third774]

Thanks for the feedback! I'll see what I can find on the webpack front.

[third774]

Would this mean we would allow for CLI arguments used on the wrangler cli to be passed to webpack? Or maybe filter down to a list of webpack specific flags?

For example, if I run wrangler build --env.mode="dev", should I expect to see that in my env object?

[xtuc]

That's a good question. I don't think we should support all the webpack-cli arguments in wrangler. I would pass an empty object. Would it make sense to you?

Also note that in #220 we are going to support passing an environment, it would be great if webpack could get access to it.

[third774]

I think passing an empty object for env makes sense for now. Once #220 is complete, it could definitely make sense to make that available as well.

Additionally, there could be some defaults that get set and merged with webpack-merge. I believe webpack-cli does this under the hood for providing the mode along with a few other things.

[xtuc]

The PR looks good to me, I would like to wait for #220, so we can pass it into the env object and make it feature complete.

[third774]

@xtuc — awesome! Is there anything I need to do to fix the CI tests?

[xtuc]

@third774 I fixed them. I think we should wait for #385 now.

[xtuc]

@third774 let's maybe not wait for env to land. I went ahead a merged this change, it will be release soon.