[WIP] Upgrade to babel@7 and support TypeScript

[turt2live]

Fixes element-hq/element-web#10524
Review with element-hq/element-web#10526
Review with matrix-org/matrix-js-sdk#1012

Upgrading to babel 7 gets a lot of the compilation stuff for free. The major changes we care about are:

• The packages are now namespaced (hence all the package changes)
• We use the env preset instead of the long-since deprecated es20XX packages.
• Added --verbose to maintain log output from the previous version.

This also meant fixing ScalarAuthClient: we can no longer mix module.exports and import in the same file.

The SdkConfig was converted to TypeScript to prove this works (it does).

This specifically does not remove flow support because that's non-trivial. Instead, we just support it and call ourselves bad people for doing it. Source code that uses flow would be the first thing I'd recommend the team replace with TypeScript, time permitting.

---

TODO:

• TypeScript basics
• Babel upgrade
• Fix i18n gen for TypeScript files
• Verify sourcemaps are a thing that moderately work
• Fix tests (if broken - they probably are)
• Fix linting (if broken - probably is)

[turt2live]

The tests here and on the js-sdk have a fun problem where the Bluebird promises are not being converted to generators correctly, so it is angry. Using native promises does not work either (it breaks even worse).

Something is going strange with how the tests babel themselves, I think. The compiled code (the app) works fine but it's obviously a blocker if the tests can't run.

The error is:

TypeError: A value [object Object] was yielded that could not be treated as a promise

Resources:

• https://stackoverflow.com/questions/35953739/a-value-was-yielded-that-could-not-be-treated-as-a-promise
• https://github.com/petkaantonov/bluebird/blob/master/docs/docs/error-explanations.md#error-a-value-was-yielded-that-could-not-be-treated-as-a-promise
• https://stackoverflow.com/questions/39463923/babel-transform-async-to-module-method-to-bluebird-with-es6-maps

However, we don't appear to be doing this either in tree or in the compiled output, so I'm not sure what's wrong. Nobody else has experienced this on the internet as far as I can tell.

The recommendation for using this generator plugin comes from chpio/babel-plugin-transform-async-to-bluebird#4 which appears to do the same thing (having looked at the diffs published by babel).

I don't really know where to proceed from here, and have given myself a maximum of 1 day to try and fix it. It's now the end of that day :(

[turt2live]

A bit of progress on the tests: It looks like the compiled library code (at least for the js-sdk) is using promises that aren't compatible with Bluebird. Wrapping awaits like await Promise.resolve(theFunction()) works, but is obviously not great considering the amount of async/await code we have.

[turt2live]

This has largely been replaced by other PRs