Bug Report

🔎 Search Terms

Type Guard

🕗 Version & Regression Information

• This changed between versions 4.9.5 and 5.0.4

⏯ Playground Link

A simple example

💻 Code

declare class Foo<Stuff extends boolean> {
  stuff: Stuff extends true ? string : string | undefined;
  isReady(): this is Foo<true> 
}
declare const x: Foo<boolean>;
if(x.isReady()) {
  x
//^? - const x: Foo<boolean>
// Should be Foo<true>
}

🙁 Actual behavior

The Type Guard didn't change the type, which is unintuitive behavior.

🙂 Expected behavior

The method should act as a type guard and change the type