Discriminated union case with a union of discriminators not correctly excluded

[SanderRonde]

Bug Report

🔎 Search Terms

discriminated union

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about discriminated union.

⏯ Playground Link

Playground link with relevant code

💻 Code

enum FooType {   Foo,   Bar,   Baz }

interface Foo{
  foo: number;
  type: FooType.Foo
}

interface BarBaz{
  type: FooType.Bar | FooType.Baz
}

function test(t: Foo | BarBaz) {
  if (t.type === FooType.Bar || t.type === FooType.Baz) {
    return
  }
  // t should only be able to be Foo here, but it can be Foo|BarBaz still.
  t.foo;

  // Alternatively this should work and we should be able to return to exclude the bar-baz case again,
  // but TS knows that `t.type` can not be either of these.
  if (t.type === FooType.Bar || t.type === FooType.Baz) {
    return;
  }
}

🙁 Actual behavior

The type of t is Foo | BarBaz while all possible cases of it being BarBaz have been excluded.

🙂 Expected behavior

The type of t is Foo.

I can imagine that this might be quite hard to fix and might have been a design (or priority) choice, but I figured I'd still submit it since you might not have seen it yet.

[Peeja]

Huh. Jinx! 😀

[MartinJohns]

Duplicate of #31404.

[SanderRonde]

Ah indeed a duplicate, will close

[typescript-bot]

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

[microsoft-github-policy-service]

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

[microsoft-github-policy-service]

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

[microsoft-github-policy-service]

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

[microsoft-github-policy-service]

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

[microsoft-github-policy-service]

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