Use typescript.sys as the module resolution host

[ghost]

But node test/comparison-tests/run-tests.js --single-test npmLink does not work.

[johnnyreilly]

Ug. Any suggestions @jbrantly?

[johnnyreilly]

Would using typescript.sys and falling back to the existing mechanism when it fails be a workaround that would allow us continue supporting npm link?

[HerringtonDarkholme]

If I remembered it correctly, referencing typescript is deliberately avoided because we don't want list TypeScript as dependency and we support other TypeScript fork implementation.

Is it still relevant today? @jbrantly @johnnyreilly what's your opinion?
Almost all forks fail to keep pace with the official compiler, leaving the official implementation the only option to use.

[jbrantly]

Re: not referencing typescript, it's hard to say. I've only known 2 typescript forks, one of which is now defunct (had JSX support) and the other was originally meant to be a nightly (ntypescript) but typescript has had their own nightlies for quite a while. My leaning is that it's probably not as big of a deal.

That said, I think it's probably also not a huge deal to fix here by just doing compiler.sys (I think?)

Regarding breaking the npmLink test... I unfortunately don't have a lot of insight into that. The original PR implementing that is #141 if that's any help.

[johnnyreilly]

Thanks @Andy-MS - this didn't get merged but the idea was used and shipped with v3.0.3 of ts-loader. The initial PR was a welcome and useful pointer so thank you.