WIP: feat: new ast for typescript 3.8

[armano2]

DO NOT MERGE,

This is branch contains so far only test scenarios for upcoming typescript 3.8.

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TODO:

• Private class properties: Add class fields and private methods estree/estree#180
• Private class method: Add class fields and private methods estree/estree#180
• Private class properties in tsx
• Export type: import type in TypeScript babel/babel#10981
• Import type: import type in TypeScript babel/babel#10981
• Export as ns from: Add exported property to ExportAllDeclaration estree/estree#205

Implemented as draft (AST may change base on tickets above:

• Private class properties
• Private class method
• Export type
  • exportKind: 'type' | 'value'
• Import type
  • importKind: 'type' | 'value'
• Export as ns from

Issues:

• There is difference in range for export * as ns between babel and ts - Add exported property to ExportAllDeclaration estree/estree#205
• createDiagnostic crashes on
  import foo, {bar} from "foo";
Cannot read property 'kind' of undefined

prettier/prettier#6608
prettier/prettier#7263
import-js/eslint-plugin-import#645
fixes #1436

[armano2]

Private class properties in tsx are supported by typescript but so far they are not documented (i'm unsure if this is intended)

i updated PR with links to estree spec proposals

[nicolo-ribaudo]

There is difference in range for export * as ns between babel and ts

Which is the difference? Is it something that should be fixed in Babel?

[armano2]

@nicolo-ribaudo for code

export * as ns from 'x'

babel reports ExportNamespaceSpecifier node at char 7, typescript node NamespaceExport is at char 12

babel: * as ns - astexplorer
typescript: ns - ts-ast-viewer

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it looks like typescript returns same range for NamespaceExport and Identifier(ns)
this seems to be an issue in typescript ast, estree/estree#202 (comment) and if it stays as is i will patch it on our side
unless estree/estree#205 is accepted, then we should return ns in ExportAllDeclaration

[dsherret]

FYI that range difference was a bug that is now fixed: microsoft/TypeScript#36762

[NickHeiner]

Is this PR actively being worked on? It looks like there haven't been any commits for a while.

Edit: I'm sorry – I didn't mean to convey a sense of entitlement. I was just looking for context for my own planning purposes.

[bradzacher]

There's a lot of work that needs to happen here.

For import/export type, they are TS specific features, so we are relatively free to implement them. However we need to be sure we're syncing up with babel so that our AST representations match. Both packages are part of one ecosystem, so we need to match up. (babel/babel#11171)

With the 3.7 release, we made the decision to jump the gun on the AST for both nullish coalescing and optional chaining, and used babel's representation. However it looks like the ESTree spec will go with a different representation, which ESLint will then build on top of. So in order to support the ecosystem, we'll have to migrate to that representation via a non-trival amount of work, and a major version bump.
This will cause a headache for any plugins using the current AST, so we want to avoid jumping the gun again.

So for private class fields/methods, and export * as ns, we taking it slow for now, to see what the official spec work is heading toward to minimise this disruption.

There is a lot of volunteers working on this across many projects, so it takes time as they find moments in their free time to work on it.

[NickHeiner]

Thanks for that context. I've updated my original comment to be clear that I don't feel entitled to anything. I appreciate the volunteers.