Ts-jest: Switch to only using babel

[GeeWee]

Babel 7 is going to have typescript support https://github.com/babel/babylon/releases/tag/v7.0.0-beta.16

Combining this with jest having their own sourcemaps might make a large patch of our codebase obsolete, and simply replaceable with a .babelrc file. We should keep an eye on this.

[kulshekhar]

This is brilliant!

I think this will make ts-jest itself unnecessary. So maybe we don't really have to do anything :)

[GeeWee]

Might be! I wouldn't mind that one bit!

[whitetrefoil]

https://github.com/babel/babel/blob/master/packages/babel-plugin-transform-typescript/README.md

According to Babel's doc, that plugin has some limitations like it cannot support namespaces, const enum, import =, export =...

I guess we still need ts-jest 😄

[kwonoj]

@whitetrefoil is correct, I gave a quick try on small repo I own and lot of TS-specific (i.e, exporting type like

type something = ...;
export {
something
}

syntax around won't work, and it's not supported scope from babel unfortunately.

[kulshekhar]

Thanks for letting us know @whitetrefoil @kwonoj

Closing this for now.