Generator's return "any" type when yielded

[rylev]

TypeScript Version: 1.8, 2.0, and nightly

Code
The following code compiles even though it would appear that result should have type string:

function* myGenerator() {
  yield "hello"
}

function* myOtherGenerator() {
  const result = yield myGenerator()
  result.methodNotAvailableOnString()
}

Expected behavior:
When a generator is yielded I expected that the type of the subsequent variable to be whatever T is in myGenerator's return type IterableIterator<T>

Actual behavior:
This is however not the case. result has type any. Should the TypeScript compiler be able to infer that that type of result should be string?

[DanielRosenwasser]

Unlike the await keyword that "grabs" the Promised value from an async function, yield does not grab the yielded value of a generator. It instead makes it available for anyone consuming the current generator. In that case, you are yielding an iterator, meaning any callers will have an iterable of iterables of strings.

The value produced by yield within a generator is the argument that you pass in to next(). This value can be anything, but can't be inferred by the structure of the generator.

function *g() {
    console.log("AAA");
    let x = yield "Hello";
    console.log("BBB");
    console.log(x);
    console.log("CCC");
}

var iter = g();
var rr = iter.next("unwitnessed"); // first call's value is 
console.log(rr.value);
iter.next("World");

Outputs:

AAA
Hello
BBB
World
CCC

If we had default type parameters, we could say that the type passed into next defaults to any, but if you want extra strictness, you could enforce it otherwise.