No IntelliSense for generic literal types

[mjbvz]

From microsoft/vscode#83375

TypeScript Version: typescript@3.8.0-dev.20191026

Search Terms:

• suggest / completions
• intellisense
• generic

Repo
For the typescript:

function test<T extends "x" | "y">() {}

test<''>

1. Trigger intellisense inside the quotes in test<''>

Expected behavior:
Suggestions for x and y returned.

Actual behavior:
No suggestions returned

[Chnapy]

Note that this issue also occurs with class heritage.

type S = 'a' | 'b' | 'c';

abstract class C<T extends S> {}

class ImplC extends C<''> {} // try autocomplete in the ''

But it works fine with variables.

type S = 'a' | 'b' | 'c';

type G<E extends S> = Readonly<E>;

let a: G<''>;  // autocomplete works fine here

[mkantor]

Is the fact that the cursor is within a string literal crucial to this issue, or would you also consider this a reproduction?

function test<T extends 1 | 2 | 3>() {}
test</* trigger completions here */>()

I'm trying to determine if/how this differs from #52898.