Calypso Build Package: Add webpack.config.js

[ockham]

Changes proposed in this Pull Request

See pafL3P-oe-p2:

Problem: Webpack config re-use is suboptimal

While we’re able to re-use parts of Calypso’s webpack config thanks to the shards concept (i.e. small files each containing specific parts of the config), the resulting webpack.config.js files are still somewhat verbose and redundant. The shards, as we are using them now, have never been the envisioned be-all, end-all, goal for an interface of a re-usable webpack config -- we even had a call with @blowery from +teamcalypsop2 on some options there (tl;dr: It’s complicated).

Solution: Parametrized `@automattic/calypso-build/webpack.config.js`

I think that as an intermediate step, it makes sense to add a parametrized webpack.config.js to @automattic/calypso-build that can then be less redundantly instantiated by consumers. The interface is still going to be suboptimal (essentially the union of all shards’ parameters), but IMO at least not worse than directly using the shards. Thanks to package versioning, we can release a new version featuring a better interface once we come up with one (and being used by a variety of different projects should help inform that interface).

The file used in here is essentially webpack.config.extensions.js minus the entry point magic, and minus CopyWebpackPlugin (about which yarn complained that it wasn't installed 🙄 -- but we might be able to get rid of that anyway, see Automattic/jetpack#11801).

Testing instructions

nvm use
cd packages/calypso-build
npm link
cd ../../
cd ../jetpack # Or wherever your local copy of Jetpack is
git checkout update/use-calypso-build-webpack-config
nvm use 10.15.2
yarn distclean && yarn
npm link @automattic/calypso-build
yarn build-extensions

Verify that blocks are built in your Jetpack directories _inc/blocks/ folder.

Follow-up (this PR or separately)

Use this config file to build o2 blocks.

/cc @sirreal @simison

[matticbot]

Test live: https://calypso.live/?branch=add/webpack-config-to-calypso-build-package

[ockham]

This choice of parametrization is supposed to organically tap into Webpack's way of accepting command line args. We should be able to use this config file with Webpack's CLI, and override these args, e.g. webpack --config ./webpack.config.js --output-filename="[chunk].js".

(Meaning I'm trying to essentially re-use Webpack's API without adding any new constraints.)

[ockham]

FYI @jeffersonrabb This might provide a nicer interface than using individual Webpack config shards for Newspack. See Automattic/jetpack#11802 for how to use it 🙂

[simison]

Would we expect to parametrize all these process.env variables?

[ockham]

We've been discussing that, e.g. using the function's env arg. We decided to merge this for an i1 since it seems to work well enough (see Automattic/jetpack#11802), and tackle those chores later.

[sirreal]

Let's get an alpha published and see how this plays out 🚀