Non-null assertion operator ignored in sub context

[KyleJune]

Bug Report

🔎 Search Terms

non-null assertion, deno, Property 'x' does not exist on type 'never'.

🕗 Version & Regression Information

This regression happened between typescript 4.2.2 and 4.3.2.

⏯ Playground Link

Playground link showing no errors in 4.2.2

Playground link showing errors in 4.3.2

💻 Code

interface Point {
  x: number;
  y: number;
}
let p: Point | null = null;
function assignP(value: Point) {
  p = value;
}
assignP({ x: 2, y: 3 });
let z: number = p!.x * p!.y;
if (p) {
  z = p!.x * p!.y;
}
console.table({ x: p!.x, y: p!.y, z });

🙁 Actual behavior

Errors inside the if block because p is inferred as never.

🙂 Expected behavior

No errors.

I also believe the non-null assertion operator in the if block should not be required since the context would only be reached if p was not null. The non-null assertion in the if block was required in 4.2.2.

[MartinJohns]

You see this behavior due to a fixed bug. See #44025.
In the end it's due to #9998.

This is a duplicate of #44025.

[MartinJohns]

You can get the behavior you want by changing your code to this:

let p = null as Point | null;