feat(typescript): Add typechecking!

[NotWoods]

Rollup Plugin Name: typescript

This PR contains:

• bugfix
• feature
• refactor
• documentation
• other

Are tests included?

• yes (bugfixes and features will not be merged without tests)
• no

Breaking Changes?

• yes (breaking changes will not be merged unless absolutely necessary)
  • Since the plugin now complains about type errors, its a breaking change.
• no

List any relevant issue numbers: #71, #105, #153

Description

Adds full typechecking support to the official Typescript plugin!

• Code frame is now included when errors are emitted
• Builds a Typescript LanguageServiceHost to work with various APIs.
• Uses Typescript's LanguageService API to compile and typecheck files.
• Changes the base tsconfig so that browser APIs aren't included by default.
• Fixes types for util/test so that functions return promises.

[shellscape]

@NotWoods if this looks good to you, merge it. Which semver are you thinking for this, minor or major?

[NotWoods]

I'm thinking of major just to be safe. The new feature is fairly large so it makes sense as a major change.

[lukastaegert]

Nice work!

One question (admittedly without checking your code): Will it still be possible to use the "old" style transformations via option? I definitely think that type-checking should be enabled by default, but the old way is still probably faster and may have other advantages for development (though it does not support const enums of course). Mainly that you can compile "dirty" code to try something out without littering everything with any casts 😉

But I do not see it as a "must have"

Which semver are you thinking for this, minor or major?

For that reason I agree that it should be major as it is breaking for people relying on this plugin compiling their broken types 😜

[NotWoods]

I plan to add the old style back in through a separate PR: https://github.com/rollup/plugins/compare/ts-type-check...NotWoods:ts-diagnostic-categories?expand=1

[NotWoods]

Should that option be included here to make migration easier?

[lukastaegert]

Not for me, you can always hold back on upgrading if it is on the roadmap