RFC: switch to Babel

[layershifter]

Previously we've decided to switch to Babel as compiler to improve our developer experience and get benefits from Babel's ecosystem like plugins. I've separated our switch to small steps that will allow us to make this process clearly.

1. Switch docs

I think that our main issue now is very slow work of yarn start i.e. start docs and we should solve this problem firstly.

Actions

• compare the performance of babel-loader & fork-ts-checker-webpack-plugin VS awesome-typescript-loader with useBabel=true

awesome-typescript-loader doesn't work properly with Babel 7, consider use babel-loader because it faster. Requires changes in project structure as we can't use required -- -isolatedModules to work properly: babel/babel#8361

Goals

• docs will start faster (performance)
• errors in types should not break webpack's process: it's really painful when everything is done and it fails on the final step.
• hot reload will work properly https://github.com/gaearon/react-hot-loader#typescript

2. Switch to @babel/register

The second step is the replacement of ts-node with @babel/register this will improve performance of all our internal scripts.

3. Switch to gulp-babel

Replace gulp-typescript with gulp-babel or even with pika-pkg: #1169.

Use existing plugins

babel-plugin-lodash & babel-plugin-transform-react-remove-prop-types will allow us to reduce bundle size for consumers.

[layershifter]

https://github.com/gaearon/react-hot-loader#typescript

As of version 4, React Hot Loader requires you to pass your code through Babel to transform it so that it can be hot-reloaded. This can be a pain point for TypeScript users, who usually do not need to integrate Babel as part of their build process.

[miroslavstastny]

Requires changes in project structure as we can't use required -- -isolatedModules to work properly

See also: babel/babel#9944

[TheAifam5]

So I can confirm that babel did not fixed the issue. Please read this: babel/babel#9895