No string completions in type arguments where constrained to string literal union

[andrewbranch]

A friend of mine recently tried using JSX generics and it seems like the fix in #34958 did not work for them.

Here is an oversimplified code snippet that replicates the issue. We've tried this in two different machines and neither worked:

import * as React from "react"

type Variations = "hello" | "baaaaa" | "click"

const MyGeneric = <T extends Variations>({  }) => {
  return <div></div>
}

const Issue = () => {
  return <MyGeneric<"ctrl+space should bring up suggestions here">></MyGeneric>
}

Originally posted by @varemenos in #34110 (comment)

[Andarist]

For the record - this isn't exclusive to JSX. It doesn't work with regular call expressions either (TS playground):

import * as React from "react"

type Variations = "hello" | "baaaaa" | "click"

const MyGeneric = <T extends Variations>({  }) => {
  return <div></div>
}

MyGeneric<"ctrl+space should bring up suggestions here">({})

[Andarist]

And it's not even about string completions:

declare function test<T extends { type: 'a' | 'b' }>(): void

test<{ type: /*1*/ }>()

test<{ type: '/*2*/' }>()

test<{ /*3*/ }>()

I didn't do further research right now to confirm this but I'm under impression that completions just don't work in type arguments.

[andrewbranch]

When I was looking for duplicates, I saw #43526, so I assumed that some support is implemented and there are just big gaps.

[kronodeus]

Here is an even more simplified example that demonstrates that functions get no completions at all for type arguments while type references do:

type OneOrTwo = "one" | "two"

// Completions do not work for functions
declare function MyFunction<T extends OneOrTwo>(): T
MyFunction<'no completions here'>()

// Completions DO work for type references
type MyType<T extends OneOrTwo> = T
MyType<'completions here'>

I can't think of a reason why completion requests for type arguments can't be routed down the same code path for functions as they are for type references.