Apply templateInterpolationService only to type-checked components

• I have searched through existing issues
• I have read through docs
• I have read FAQ

Info

• Platform: macOS
• Vetur version: 0.22.2
• VS Code version: 1.38.0

Problem

Feature Request - add a third option for templateInterpolationService, ts-only

As mentioned in #1246, the templateInterpolationService works well in a lot of cases, but will quite regularly throw errors for JavaScript components, because without proper attention paid to adding type annotations to a component using lang="ts", it’s very unlikely that a JS Vue component will be able to be parsed correctly.

So, in JS components, there are a lot of errors that end up looking like this, when setting "vetur.experimental.templateInterpolationService": true

In our case, and potentially other repos that are attempting to get TS benefits in a codebase that was originally JS-only, some components are TS, while many remain JS.

It seems likely that only TS components will see useful benefits from templateInterpolationService, so the proposal is to add a third option to the settings, ts-only

Changing these lines to something like

"vetur.experimental.templateInterpolationService": {
	"type": ["boolean", "string"],
	"default": false,
	"description": "Enable template interpolation service that offers diagnostics / hover / definition / references. Use 'ts-only' to enable only for TypeScript components"
}

I’m sure the above can be done much better, hopefully with enum, while still maintaining backwards compatibility (default still false, still allowing true & applying to all files).

I’m very happy to work on this change, if it’s an acceptable request & the use case (JS & TS components in the same project, or at least the same workspace) is common enough. I don’t have any significant extension development experience, so any other recommendations on how to structure the config option are welcome.

Reproducible Case

(happy to add a modified Veturpack with both JS & TS components, if that’s useful)

[rchl]

Yes, I have checkJs enabled and I have typechecking enabled in script block. And now I understand your intention and I’m fine with template interpolation only be enabled when @ts-check or checkJs is enabled.

[ktsn]

I feel a bit weird that you expect template type check while <script> block doesn’t (without @ts-check or checkJs in ts compiler). If you are ok with adding type annotation via JS docs, maybe you can just enable checkJs, can’t you?