union type is unexpectedly narrowed by ternary

[oatkiller]

Bug Report

🔎 Search Terms

ternary union narrow

🕗 Version & Regression Information

Verified using the playground with versions 3.3.3 through 4.4.4. Also tried nightly. I reviewed the common-bugs-that-arent-bugs comment for similar issues.

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about type narrowing / guarding (I skimmed the whole page.)

⏯ Playground Link

Playground link with relevant code

💻 Code

type A = { foo: string;}
type B = A & { bar : string;}

declare const binding: A | B;

// type is `A` but was expected to be `A | B`
const secondBinding = true ? binding : binding;

if ('bar' in secondBinding) {
  secondBinding.bar;
}

🙁 Actual behavior

binding has type A | B and was assigned to secondBinding. secondBinding has type A, but its type should've been inferred as the same type: A | B.

🙂 Expected behavior

secondBinding should have the same type as binding because it's assigned that way.

[oatkiller]

The behavior is equivalent if A and B are interfaces.

[MartinJohns]

Duplicate of ##46449.

[oatkiller]

@MartinJohns Thanks!