(🐞) No error when assigning to a member of a union that has different types in each part of the union

[KotlinIsland]

Bug Report

🔎 Search Terms

union container assignment

🕗 Version & Regression Information

v4.8.0-beta

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about: generic unions

⏯ Playground Link

Playground link with relevant code

💻 Code

class A {
    t!: number
}

class B {
    t!: string
}

declare let a: A | B
a.t = "a string?"

🙁 Actual behavior

No error when assigning a string to the incompatible item of the union (number)

🙂 Expected behavior

An error regarding the invalid assignment.

[MartinJohns]

Pretty sure it's a duplicate of #50249.

[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.