Bug: incorrect contextual typing on yield expression of generator function as discriminate of a union

[shigma]

Bug Report

🔎 Search Terms

generator function union contextual typing yield expression

🕗 Version & Regression Information

4.8.4

⏯ Playground Link

Playground link with relevant code

💻 Code

type Action = () => (Generator<string, string, string[]> | string)

const b: Action = function* () {
    // expect `string[]`, actual `never`
    const c = yield ''
    return ''
}

🙁 Actual behavior

never

🙂 Expected behavior

string[]

[shigma]

Other cases:

unknown: