Support TypeScript 4.1

[sosukesuzuki]

TypeScript 4.1 beta has been released!

• typescript-eslint: TypeScript 4.1 Syntax Support typescript-eslint/typescript-eslint#2583

We should support new syntax:

Template Literal Types

https://devblogs.microsoft.com/typescript/announcing-typescript-4-1-beta/#template-literal-types

type Greeting = `hello ${World}`;

Key Remapping in Mapped Types

https://devblogs.microsoft.com/typescript/announcing-typescript-4-1-beta/#key-remapping-mapped-types

type MappedTypeWithNewKeys<T> = {
    [K in keyof T as NewKeyType]: T[K]
}

[sosukesuzuki]

Babel 7.12 that supports TypeScript 4.1 has been released!. So we can support TypeScript 4.1 via babel-ts parser.

[schickling]

Thanks a lot for adding support for TS 4.1. Is the functionality merged with #9473 already released/published somewhere to be tested?

[sosukesuzuki]

@schickling You can try to use TS 4.1 support via Babel with Installing from GitHub. See https://prettier.io/versions.html.(Need to run npm install prettier/prettier. )
Also need to update your configuration file to use babel-ts parser. See https://prettier.io/docs/en/options.html#parser and https://prettier.io/docs/en/configuration.html#configuration-overrides.

[aleclofabbro]

Thanks for the effort on this issue !
2 Qs:
how can I get notified when a stable version will be released ?
Are you aware of a way to enable vscode's prettier extension with TS4.1 support (type templates at least) ?

[wdoug]

I'm just curious to follow up on that last question. Now that TypeScript 4.1 is officially released, I saw you @sosukesuzuki had mentioned opening a separate PR for releasing this. Any idea when that might be ready or if there is anything we could do to help get this pushed to npm?

[sosukesuzuki]

@wdoug Thank you! I've created the PR that update to TypeScript 4.1. We can work for releasing after merge #9725.