transformers support

[rifler]

Hello!

As you probably know, TypeScript has Compiler API, which allows to create "transformers" - functions in which you get control over AST and change it as you wish.
Unfortunately, to use this transformers you should completely duplicate the whole tsc command yourself. It is inconvenient.
Feature request to implement support for transformers right into tsconfig.json - microsoft/TypeScript#14419

Fortunately, there are some solutions, which patch tsc command and make it to respect transformers defined it tsconfig.json. So they are executed at build time. I guess the most popular tool is ttypescript.

Also, there are several packages quite similar to tsconfig-paths, which provides ttypescript support for build-time paths transformations, for instance:
https://github.com/OniVe/ts-transform-paths
https://github.com/zerkalica/zerollup/tree/master/packages/ts-transform-paths
https://github.com/LeDDGroup/typescript-transform-paths

But they are not so popular, tested and maintained as tsconfig-paths.

I suppose it would be great to export ready transformer from tsconfig-paths. This would allow to dramatically cut off entropy and produce path's transformations during build time.

[Farenheith]

I created a plugin for it and tested it with jest. It worked as expected. Can you try it on too?

#273

I also created this package to be used while the PR is not approved: https://www.npmjs.com/package/tsconfig-paths-hook