Double (exclusion) inference doesn't narrow union object

[exoRift]

🔎 Search Terms

"double inference", "exclusion inference", "union object narrow"

🕗 Version & Regression Information

I observed this issue on versions

• 5.4.5
• 5.7.3

⏯ Playground Link

https://www.typescriptlang.org/play/?ts=5.7.3#code/C4TwDgpgBAKhDOwoF4oAoDeBYAUFfUAxgBYSEDWAXFAOQBOCA9gDYBuEAJjbgVMMQEsAdgHNqQgK4BbAEYQ6uAL5QAPlGx4CJMlVrNGAQw7CRNVbXl1GDLjwL8T1CUI4QAZsM5KAlLlyFGIUQoN0ZGajhg1AxlA3hYBGA-HAE3dFDGADptChRkVBp9IxMzFTUM7NJc-ILLa04ab3U7fAqc8haoAHouqAA9AH5OiodRTp7+oZxlCGZ4aA1eNqqOzXwJweGwzNGRcd7N6dwgA

💻 Code

type Test = ({
    check: 'resolved'
    thing: number
} | {
    check: 'loading' | 'errored'
    thing: undefined
})

const foo: Test = {} as Test

if (foo.check === 'loading' || foo.check === 'errored') {
    foo.check
    // ^?
    foo.thing
    // ^?
} else {
    foo.check
    // ^?
    foo.thing
    // ^?

  // `foo.check` is `'resolved'` here, but `foo.thing` is still `number | undefined`
}

🙁 Actual behavior

foo.check` is `'resolved'` here, but `foo.thing` is still `number | undefined

This is impossible considering the type

type Test = ({
    check: 'resolved'
    thing: number
} | {
    check: 'loading' | 'errored'
    thing: undefined
})

🙂 Expected behavior

I expected foo.thing to be of type number since foo.check is of type 'resolved'

Additional information about the issue

No response

[IllusionMH]

Duplicate of #56023, #31404 etc.

[exoRift]

Duplicate of #56023, #31404 etc.

What is the original issue? Is this planned to be fixed?

[exoRift]

I've devised a workaround for this issue which is to split the property's string union into an upper-level object union

https://www.typescriptlang.org/play/?ts=5.7.3#code/C4TwDgpgBAKhDOwoF4oG8CwAoKuoGMALCfAawC4oByAJwQHsAbANwgBMrs8phCBLAHYBzSgICuAWwBGEGtgC+UAD7oueIiQrVG9AIZtBQqsuqya9OhzW5ehymIFsIAM0HsF2bPnoDEUZ-T0lHB+qGiKuvCwCMCeWHzOUAAUAfQAdBpkKMioVDr6hsZKKqkZxFk5uWYW7FQAlKo4eKWZpNZQAPQdUAB6APztpbbC7V29A1iKEIzw0JhNuC3lbQud3f2DgWnDQqPrE-JxoJBQAOoWpLrmDmwojdytlLQMLLXtO6KSMnKTJklJ8weyye+QMwk4vxUgPUwNMNHMlgh8gaADJ7ngPlAbi43GwFHU4t5fEgpFdKOcaJdro47uEoJEzhcrvQbnEEslSTQyppsrlQYVlCpOdyKjk4Qjag1obhha09uN2sKdvKNr9prN0TKriKVtwxqruEr+CNVvqDtggA

[MartinJohns]

What is the original issue? Is this planned to be fixed?

He linked the original issue. It's marked as design limitation, so it's unlikely to be solved anytime soon.

[typescript-bot]

This issue has been marked as "Duplicate" and has seen no recent activity. It has been automatically closed for house-keeping purposes.