ttypescript VS simple-ts-transform

Actually this can easily overcome by using https://github.com/cevek/ttypescript that allows using transformers in tsc and define then in tsconfig.json

You could write custom transformer for this (using ttypescript), if you really want to

didn't look to hard at it but afaik ttypescript is what you need https://github.com/cevek/ttypescript

That's it! after this, just register it with the method described on ttypescript.

As I noted above, this is a TypeScript transformer plugin so it needs to hook this plugin on TypeScript compilation phase. I suppose one of the easiest ways is using ttypescript which is a custom TypeScript compiler that can hook the transformer plugin on a compilation. Please refer also to the "How to use this transformer" section in README.

If you don't want to use a bundler, you can use https://github.com/cevek/ttypescript in combination with https://github.com/LeDDGroup/typescript-transform-paths

You can use the plugin https://github.com/awerlogus/io-ts-transformer with https://github.com/cevek/ttypescript to get compile time generation of io-ts codecs as well.

There is also a forked version of the compiler that allows custom transformers: https://github.com/cevek/ttypescript

Closest I can think of is ttypescript

My point is, instead of *forking* Typescript, why not just write a transform? Instead of creating new syntax, write up a visitor that will walk through something that looks like a result type and output the JS code that handles it correctly. This is how things like optional chaining were supported before they were incorporated into the compiler. Here's a similar question from a few weeks ago that I responded to in more detail.